Publications de l'équipe Thermodynamique Ondes Numérique Interfaces Combustion
2017
Alexandre Chiapolino, Richard Saurel, Boniface Nkonga. Sharpening diffuse interfaces with compressible fluids on unstructured meshes. Journal of Computational Physics, Elsevier, 2017, 340, pp.389-417. Plus de détails...
François-Joseph Chatelon, Jacques-Henri Balbi, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli. A convective model for laboratory fires with well-ordered vertically-oriented fuel beds. Fire Safety Journal, Elsevier, 2017, 90, pp.54-61. Plus de détails...
Several studies in the literature explore the connection between rate of spread (ROS) and wind in wildland fires. These studies show very different positions about the role of radiation and convection as heat transfer mechanisms. In the case when the fuel bed is well-ordered and vertically-oriented, there seems to be a consensus leading to suggest that convective heating is the dominant heat transfer mode in that case. The purpose of this work is to propose a convective semi-physical model for the behaviour of the rate of spread in wind, when the fuel bed is vertically-oriented. Due to a specific fuel bed arrangement, flame radiation –i.e. radiation from the part of the flame above the vegetal stratum– is neglected. Only horizontal radiation from the fuel burning particles area and convective heating are taken into account. Convective heat transfer is assumed to be the primary heat transfer mechanism. The proposed model is confronted to 172 laboratory fires with a wide range of fuel characteristics. The predicted results are also compared with two simplified models from the literature. Statistical tools are used to check the agreement between the predicted ROS and the observed one where a strong agreement is generally observed, irrespective of fuel bed characteristics.
François-Joseph Chatelon, Jacques-Henri Balbi, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli. A convective model for laboratory fires with well-ordered vertically-oriented fuel beds. Fire Safety Journal, Elsevier, 2017, 90, pp.54-61. <hal-01525409>
J Gubspun, C De Loubens, R Trozzo, Johnny Deschamps, M Georgelin, et al.. Perturbations of the flow induced by a microcapsule in a capillary tube. Fluid Dynamics Research, IOP Publishing, 2017, 49 (3), . Plus de détails...
Soft microcapsules moving in a cylindrical capillary deform from quasi-spherical shapes to elongated shapes with an inversion of curvature at the rear. We investigated the perturbation of the flow by particle tracking velocimetry around deformed microcapsules in confined flow. These experiments are completed by numerical simulations. Microcapsules are made of a thin membrane of polymerized human albumin and their shear elastic moduli are previously characterized in a cross flow chamber. Firstly, the velocity of the microcapsule can be calculated by theoretical predictions for rigid spheres, even for large deformations as 'parachute- like' shapes, if a relevant definition of the ratio of confinement is chosen. Secondly, at the rear and the front of the microcapsule, the existence of multiple recirculation regions is governed by the local curvature of the membrane. The amplitudes of these perturbations increase with the microcapsule deformation, whereas their axial extents are comparable to the radius of the capillary whatever the confinement and the capillary number. We conclude that whereas the motion of microcapsules in confined flow has quantitative similitudes with rigid spheres in terms of velocity and axial extent of the perturbation, their presence induces variations in the flow field that are related to the local deformation of the membrane as in droplets.
J Gubspun, C De Loubens, R Trozzo, Johnny Deschamps, M Georgelin, et al.. Perturbations of the flow induced by a microcapsule in a capillary tube. Fluid Dynamics Research, IOP Publishing, 2017, 49 (3), <10.1088/1873-7005/aa6270>. <hal-01590334>
Saptarshi Bhattacharjee, Guillaume Ricciardi, Stéphane Viazzo. Comparative study of the contribution of various PWR spacer grid components to hydrodynamic and wall pressure characteristics. Nuclear Engineering and Design, Elsevier, 2017, 317, pp.22 - 43. Plus de détails...
Flow-induced vibrations in a pressurized water reactor (PWR) core can cause fretting wear in fuel rods. These vibrations can compromise safety of a nuclear reactor. So, it is necessary to know the random fluctuating forces acting on the rods which cause these vibrations. In this paper, simplified 3D models like square spacer grid, circular spacer grid and symmetric mixing vanes have been used inside an annular pipe. Hydrodynamic and wall pressure characteristics are evaluated using large eddy simulations (LES). Structured meshes are generated as far as possible. Simulations are compared with an experiment. Results show that the grid and vanes have a combined effect: grid accelerates the flow whereas the vanes contribute to the swirl structures. Spectral analysis of the simulations illustrate vortex shedding phenomenon in the wake of spacer grids. This initial study opens up interesting perspectives towards improving the modeling strategy and understanding the complex phenomenon inside a PWR core. (C) 2017 Elsevier B.V. All rights reserved.
Saptarshi Bhattacharjee, Guillaume Ricciardi, Stéphane Viazzo. Comparative study of the contribution of various PWR spacer grid components to hydrodynamic and wall pressure characteristics. Nuclear Engineering and Design, Elsevier, 2017, 317, pp.22 - 43. <10.1016/j.nucengdes.2017.03.011>. <hal-01590274>
François Joseph Chatelon, Jacques Henri Balbi, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli. A convective model for laboratory fires with well-ordered vertically-oriented fuel beds. Fire Safety Journal, Elsevier, 2017, 90, pp.54 - 61. Plus de détails...
Several studies in the literature explore the connection between rate of spread (ROS) and wind in wildland fires. These studies show very different positions about the role of radiation and convection as heat transfer mechanisms. In the case when the fuel bed is well-ordered and vertically-oriented, there seems to be a consensus leading to suggest that convective heating is the dominant heat transfer mode in that case. The purpose of this work is to propose a convective semi-physical model for the behaviour of the rate of spread in wind, when the fuel bed is vertically-oriented. Due to a specific fuel bed arrangement, flame radiation -i.e. radiation from the part of the flame above the vegetal stratum is neglected. Only horizontal radiation from the fuel burning particles area and convective heating are taken into account. Convective heat transfer is assumed to be the primary heat transfer mechanism. The proposed model is confronted to 172 laboratory fires with a wide range of fuel characteristics. The predicted results are also compared with two simplified models from the literature. Statistical tools are used to check the agreement between the predicted ROS and the observed one where a strong agreement is generally observed, irrespective of fuel bed characteristics.
François Joseph Chatelon, Jacques Henri Balbi, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli. A convective model for laboratory fires with well-ordered vertically-oriented fuel beds. Fire Safety Journal, Elsevier, 2017, 90, pp.54 - 61. <10.1016/j.firesaf.2017.04.022>. <hal-01590266>
Journal: Fire Safety Journal
Date de publication: 01-06-2017
Auteurs:
François Joseph Chatelon
Jacques Henri Balbi
Dominique Morvan
Jean Louis Rossi
Thierry Marcelli
2017
Alexandre Chiapolino, Pierre Boivin, Richard Saurel. A simple and fast phase transition relaxation solver for compressible multicomponent two-phase flows. Computers and Fluids, Elsevier, 2017, 150, pp.31 - 45. Plus de détails...
The present paper aims at building a fast and accurate phase transition solver dedicated to unsteady multiphase flow computations. In a previous contribution (Chiapolino et al. 2017), such a solver was successfully developed to compute thermodynamic equilibrium between a liquid phase and its corresponding vapor phase. The present work extends the solver's range of application by considering a multicomponent gas phase instead of pure vapor, a necessary improvement in most practical applications. The solver proves easy to implement compared to common iterative procedures, and allows systematic CPU savings over 50%, at no cost in terms of accuracy. It is validated against solutions based on an accurate but expensive iterative solver. Its capability to deal with cavitating, evaporating and condensing two-phase flows is highlighted on severe test problems both 1D and 2D.
Alexandre Chiapolino, Pierre Boivin, Richard Saurel. A simple and fast phase transition relaxation solver for compressible multicomponent two-phase flows. Computers and Fluids, Elsevier, 2017, 150, pp.31 - 45. <10.1016/j.compfluid.2017.03.022>. <hal-01502389>
Pierre Boivin, A.L. Sánchez, F.A. Williams. Analytical prediction of syngas induction times. Combustion and Flame, Elsevier, 2017, 176, pp.489 - 499. Plus de détails...
Rachel Aganetti, Aymeric Lamorlette, G.R. Thorpe. The relationship between external and internal flow in a porous body using the penalisation method. International Journal of Heat and Fluid Flow, Elsevier, 2017, 66 (66), pp.185 - 196. Plus de détails...
Stockpiles of organic porous materials such as biosolids, coal, compost and woodchips are susceptible to spontaneous combustion. Flow fields within such materials are induced by buoyant forces and external agents such as the wind. However, the external forces may vary on a time scale of seconds, whereas the heat, mass and momentum processes within the porous medium may occur over timescales days or months. It would be computationally prohibitive to resolve all of the timescales, hence in this paper mean external forces are coupled to the flow field within stockpiles of biosolids by means of a penalisation method. It has been determined that four variables have a profound influence of the flow fields within porous media. These are the velocity of the wind, the permeability of the porous biosolids, the angle of repose of the medium and aspect ratio of the stockpile. Four distinct flow regimes within the stockpiles have been identified. A correlation has been developed to assist managers of stockpiles, which relates mean velocities within the four flow regimes with a Darcy and Reynolds number, the aspect ratio and angle of repose. The correlation is accurate for two of the four flow regions identified, but the error in predicting the two remaining regions is relatively large. However, this error is expected to have minimal impact on estimating the time for spontaneous combustion to occur.
Rachel Aganetti, Aymeric Lamorlette, G.R. Thorpe. The relationship between external and internal flow in a porous body using the penalisation method. International Journal of Heat and Fluid Flow, Elsevier, 2017, 66 (66), pp.185 - 196. <10.1016/j.ijheatfluidflow.2017.06.003>. <hal-01547073>
Journal: International Journal of Heat and Fluid Flow
Romain Thimothée, Christian Chauveau, Fabien Halter, Colette Nicoli, Pierre Haldenwang, et al.. Microgravity experiments and numerical studies on ethanol/air spray flames. Comptes Rendus Mécanique, Elsevier Masson, 2017, 345 (2), pp.99 - 116. Plus de détails...
Spray flames are known to exhibit amazing features in comparison with single-phase flames. The weightless situation offers the conditions in which the spray characteristics can be well controlled before and during combustion. The article reports on a joint experimental/numerical work that concerns ethanol/air spray flames observed in a spherical chamber using the condensation technique of expansion cooling (based on the Wilson cloud chamber principle), under microgravity. We describe the experimental setup and give details on the creation of a homogeneous and nearly monosized aerosol. Different optical diagnostics are employed successfully to measure the relevant parameters of two-phase combustion. A classical shadowgraphy system is used to track the flame speed propagation and allow us to observe the flame front instability. The complete characterization of the aerosol is performed with a laser diffraction particle size analyser by measuring the droplet diameter and the droplet density number, just before ignition. A laser tomography device allows us to measure the temporal evolution of the droplet displacement during flame propagation, as well as to identify the presence of droplets in the burnt gases. The numerical modelling is briefly recalled. In particular, spray-flame propagation is schematized by the combustion spread in a 2-D lattice of fuel droplets surrounded by an initial gaseous mixture of fuel vapour and air. In its spherical expansion, the spray flame presents a corrugated front pattern, while the equivalent single-phase flame does not. From a numerical point of view, the same phenomena of wrinkles are also observed in the simulations. The front pattern pointed out by the numerical approach is identified as of Darrieus–Landau (DL) type. The droplets are found to trigger the instability. Then, we quantitatively compare experimental data with numerical predictions on spray-flame speed. The experimental results show that the spray-flame speed is of the same order of magnitude as that of the single-phase premixed flame. On the other hand, the numerical results exhibit the role played by the droplet radius in spray-flame propagation, and retrieve the experiments only when the droplets are small enough and when the Darrieus–Landau instability is triggered. A final discussion is developed to interpret the various patterns experimentally observed for the spray-flame front.
Romain Thimothée, Christian Chauveau, Fabien Halter, Colette Nicoli, Pierre Haldenwang, et al.. Microgravity experiments and numerical studies on ethanol/air spray flames. Comptes Rendus Mécanique, Elsevier Masson, 2017, 345 (2), pp.99 - 116. <10.1016/j.crme.2016.10.013>. <hal-01441677>
H Berjamin, N Favrie, B Lombard, G Chiavassa. Nonlinear waves in solids with slow dynamics: an internal-variable model. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, The, 2017, 473, pp.20170024. Plus de détails...
In heterogeneous solids such as rocks and concrete, the speed of sound diminishes with the strain amplitude of a dynamic loading (softening). This decrease known as " slow dynamics " occurs at time scales larger than the period of the forcing. Also, hysteresis is observed in the steady-state response. The phenomenological model by Vakhnenko et al. is based on a variable that describes the softening of the material [Phys. Rev. E 70-1, 2004]. However, this model is 1D and it is not thermodynamically admissible. In the present article, a 3D model is derived in the framework of the finite strain theory. An internal variable that describes the softening of the material is introduced, as well as an expression of the specific internal energy. A mechanical constitu-tive law is deduced from the Clausius-Duhem inequality. Moreover, a family of evolution equations for the internal variable is proposed. Here, an evolution equation with one relaxation time is chosen. By construction, this new model of continuum is thermodynamically admissible and dissipative (inelas-tic). In the case of small uniaxial deformations, it is shown analytically that the model reproduces qualitatively the main features of real experiments.
H Berjamin, N Favrie, B Lombard, G Chiavassa. Nonlinear waves in solids with slow dynamics: an internal-variable model. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Royal Society, The, 2017, 473, pp.20170024. <hal-01517335>
Journal: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
H Berjamin, B Lombard, G Chiavassa, N Favrie. Analytical solution to the Riemann problem of 1D elastodynamics with general constitutive laws . Wave Motion, Elsevier, 2017, 74, pp.35-55. Plus de détails...
Under the hypothesis of small deformations, the equations of 1D elastodynamics write as a 2 × 2 hyperbolic system of conservation laws. Here, we study the Riemann problem for convex and nonconvex constitutive laws. In the convex case, the solution can include shock waves or rarefaction waves. In the nonconvex case, compound waves must also be considered. In both convex and nonconvex cases, a new existence criterion for the initial velocity jump is obtained. Also, admissibility regions are determined. Lastly, analytical solutions are completely detailed for various constitutive laws (hyperbola, tanh and polynomial), and reference test cases are proposed.
H Berjamin, B Lombard, G Chiavassa, N Favrie. Analytical solution to the Riemann problem of 1D elastodynamics with general constitutive laws . Wave Motion, Elsevier, 2017, 74, pp.35-55. <hal-01350116>
Evelyne Neau, Isabelle Raspo, Joan Escandell. The NRTL-PRA group contribution EoS for the simultaneous prediction of LLE, VLE and hE of hydrocarbon mixtures with associating compounds. Fluid Phase Equilibria, Elsevier, 2016, 427, pp.126-142. Plus de détails...
The goal of this study is to propose a modification of the NRTL-PR EoS for the prediction of phase equilibria and excess enthalpies in mixtures containing methanol with hydrocarbons; indeed, with these systems, the original equation is confronted to many difficulties arising from the simultaneous prediction of liquid-liquid equilibria together with vapor-liquid and enthalpy data. For this purpose, an additional term is included in the EoS excess Gibbs energy, , of the Peng-Robinson equation to account for the self-association of methanol. The resulting NRTL-PRA EoS is successfully used for the prediction of both liquid-liquid and vapor-liquid equilibria, as well as excess enthalpies, in mixtures of methanol with hydrocarbons, light gases and associating compounds. Results are comparable to those obtained with other predictive EoS (VTPR and SAFT), but with the main advantage to predict all thermodynamic properties with a simple cubic equation.
Evelyne Neau, Isabelle Raspo, Joan Escandell. The NRTL-PRA group contribution EoS for the simultaneous prediction of LLE, VLE and hE of hydrocarbon mixtures with associating compounds. Fluid Phase Equilibria, Elsevier, 2016, 427, pp.126-142. <10.1016/j.fluid.2016.06.035>. <hal-01369874>
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, Elsevier, 2016, 117, pp.203-218. Plus de détails...
In this study, adsorption in a model binary mixture is investigated near the critical point in a side-heated cavity. The diverging behavior of the equilibrium constant and the Piston effect are taken into account and their influence on the adsorption process is pointed to. The modeling is based on numerical integration of the differential equations, considering the Navier-Stokes equations coupled with the energy and mass diffusion balances. By means of this model, the temperature, density and adsorbed concentration profiles are drawn at different times. Some fundamental concepts about the system’s response to the heating are illustrated. The results reveal that the adsorption process is influenced by the combined effect of several parameters, such as the gravity and the proximity to the critical point. In particular, the adsorbed amount exhibits a reversed dependency on the wall heating very close to the critical point, which confirms the complexity of such a process in binary systems near critical conditions.
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, Elsevier, 2016, 117, pp.203-218. <10.1016/j.supflu.2016.06.020>. <hal-01369830>
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, Elsevier, 2016, 117, pp.203-218. Plus de détails...
In this study, adsorption in a model binary mixture is investigated near the critical point in a side-heated cavity. The diverging behavior of the equilibrium constant and the Piston effect are taken into account and their influence on the adsorption process is pointed to. The modeling is based on numerical integration of the differential equations, considering the Navier-Stokes equations coupled with the energy and mass diffusion balances. By means of this model, the temperature, density and adsorbed concentration profiles are drawn at different times. Some fundamental concepts about the system’s response to the heating are illustrated. The results reveal that the adsorption process is influenced by the combined effect of several parameters, such as the gravity and the proximity to the critical point. In particular, the adsorbed amount exhibits a reversed dependency on the wall heating very close to the critical point, which confirms the complexity of such a process in binary systems near critical conditions.
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, Elsevier, 2016, 117, pp.203-218. <10.1016/j.supflu.2016.06.020>. <hal-01369830>
Evelyne Neau, Isabelle Raspo, Joan Escandell. The NRTL-PRA group contribution EoS for the simultaneous prediction of LLE, VLE and hE of hydrocarbon mixtures with associating compounds. Fluid Phase Equilibria, Elsevier, 2016, 427, pp.126-142. Plus de détails...
The goal of this study is to propose a modification of the NRTL-PR EoS for the prediction of phase equilibria and excess enthalpies in mixtures containing methanol with hydrocarbons; indeed, with these systems, the original equation is confronted to many difficulties arising from the simultaneous prediction of liquid-liquid equilibria together with vapor-liquid and enthalpy data. For this purpose, an additional term is included in the EoS excess Gibbs energy, , of the Peng-Robinson equation to account for the self-association of methanol. The resulting NRTL-PRA EoS is successfully used for the prediction of both liquid-liquid and vapor-liquid equilibria, as well as excess enthalpies, in mixtures of methanol with hydrocarbons, light gases and associating compounds. Results are comparable to those obtained with other predictive EoS (VTPR and SAFT), but with the main advantage to predict all thermodynamic properties with a simple cubic equation.
Evelyne Neau, Isabelle Raspo, Joan Escandell. The NRTL-PRA group contribution EoS for the simultaneous prediction of LLE, VLE and hE of hydrocarbon mixtures with associating compounds. Fluid Phase Equilibria, Elsevier, 2016, 427, pp.126-142. <10.1016/j.fluid.2016.06.035>. <hal-01369874>
Romain Oguic, Sébastien Poncet, Stéphane Viazzo. High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity. International Journal of Heat and Fluid Flow, Elsevier, 2016, 61 (B), pp.366-378. Plus de détails...
The present work reports Direct Numerical Simulations (DNS) of an impinging round jet onto a rotating heated disk in a confined rotor-stator cavity. The geometrical characteristics of the system correspond to the experimental set-up developed by u. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.]. The aspect ratio of the cavity G = h/R-d between the interdisk spacing h and the rotor radius R-d is fixed to 0.02 corresponding to a narrow-gap cavity. The axial Reynolds number Red based on the jet characteristics is also fixed to Re-j = 5300, while the rotational Reynolds number Re-Omega may vary to preserve the swirl parameter N proportional to Re(Omega)dRe(j) (0 <= N <= 2.47) between the present simulations and the experimental data of [J. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.] and [T. D. Nguyen, J. Pelle, S. Harmand, and S. Poncet. PIV measurements of an air jet impinging on an open rotor-stator system. Experiments in Fluids, 53:401-412, 2012.] for comparisons. The results are discussed in terms of radial distributions of the mean velocity components and corresponding Reynolds stress tensor components. The swirl parameter does not modify the size of the recirculation bubble developed along the stator close to the pipe exit. For N >= 1.237, centrifugal effects at the rotor periphery are balanced by a centripetal flow along the stator. Some spiral patterns develop then in the stator boundary layer corresponding to the SRIII instability of [L. Schouveiler, P. Le Gal, and M. P. Chauve. Instabilities of the flow between a rotating and a stationary disk. Journal of Fluid Mechanics, 443:329-350, 2001.] in an enclosed cavity. The numerical results are found to agree particularly well with the experimental data in terms of the distribution of the local Nusselt number along the rotor. Finally, a correlation for its averaged value is proposed according to the swirl parameter. (C) 2016 Elsevier Inc. All rights reserved.
Romain Oguic, Sébastien Poncet, Stéphane Viazzo. High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity. International Journal of Heat and Fluid Flow, Elsevier, 2016, 61 (B), pp.366-378. <10.1016/j.ijheatfluidflow.2016.05.013>. <hal-01461786>
Journal: International Journal of Heat and Fluid Flow
Alexandre Chiapolino, Pierre Boivin, Richard Saurel. A simple phase transition relaxation solver for liquid-vapor flows. International Journal for Numerical Methods in Fluids, Wiley, 2016, . Plus de détails...
Determining liquid-vapor phase equilibrium is often required in multiphase flow computations. Existing equilibrium solvers are either accurate but computationally expensive, or cheap but inaccurate. The present paper aims at building a fast and accurate specific phase equilibrium solver, specifically devoted to unsteady multiphase flow computations. Moreover, the solver is efficient at phase diagram bounds, where non-equilibrium pure liquid and pure gas are present. It is systematically validated against solutions based on an accurate (but expensive) solver. Its capability to deal with cavitating, evaporating and condensing two-phase flows is highlighted on severe test problems both 1D and 2D.
Alexandre Chiapolino, Pierre Boivin, Richard Saurel. A simple phase transition relaxation solver for liquid-vapor flows. International Journal for Numerical Methods in Fluids, Wiley, 2016, <10.1002/fld.4282>. <hal-01359203>
Journal: International Journal for Numerical Methods in Fluids
Salim Bounoua, Séverine Tomas, Jérôme Labille, Bruno Molle, Jacques Granier, et al.. Understanding physical clogging in drip irrigation: in situ, in-lab and numerical approaches. Irrigation Science, Springer Verlag, 2016, 34 (4), pp.327-342. Plus de détails...
Dripper clogging is a major drawback of microirrigation systems that must be addressed to improve their efficiency and durability. Particle-induced clogging is first studied in situ. The experiments consist in observing in real conditions the behavior of a series of drippers fitted on an agricultural plot in the south of France. The plot is supplied from a canal with Durance River water. The latter is loaded with sediments that gradually clog drippers and filters. Water analysis reveal that physicochemical clogging prevails over biological clogging. This characterization helps in setting in-lab experiment protocol. Indeed, besides field observation of clogging, laboratory analyses of both the irrigation water and the clogging material are performed with reactive and inert clay: smectite and an illite-calcite mix. A surprising tendency is observed: Salt concentration in smectite seeded water decreases the clogging, whereas it increases agglomerate size. Computational fluid dynamic simulations are carried out to investigate the impact of particles on flow behavior. Results demonstrate that clay particles interacting with the flow govern the complex structure of the fluid velocity fields inside the dripper labyrinth channel.
Salim Bounoua, Séverine Tomas, Jérôme Labille, Bruno Molle, Jacques Granier, et al.. Understanding physical clogging in drip irrigation: in situ, in-lab and numerical approaches. Irrigation Science, Springer Verlag, 2016, 34 (4), pp.327-342. <10.1007/s00271-016-0506-8>. <hal-01519534>
Richard Saurel, Pierre Boivin, Olivier Le Métayer. A general formulation for cavitating, boiling and evaporating flows. Computers and Fluids, Elsevier, 2016, 128, pp.53-64. Plus de détails...
A flow model is derived for the numerical simulation of multi-phase flows with phase transition. The model arises from the classical multi-component Euler equations, but is associated to a non-classical thermodynamic closure: each phase is compressible and evolves in its own subvolume, with phases sharing common pressure, velocity and temperature, leading to non-trivial thermodynamic relations for the mixture. Phase transition is made possible through the introduction of Gibbs free energy relaxation terms in the equations. Capillary effects and heat conduction – essential in boiling flows – are introduced as well. The resulting multi-phase flow model is hyperbolic, valid for arbitrary density jumps at interfaces as well as arbitrary flow speeds. Its capabilities are illustrated successively through examples of nozzle induced cavitation, a high-speed evaporating liquid jet, and heated wall induced boiling.
Richard Saurel, Pierre Boivin, Olivier Le Métayer. A general formulation for cavitating, boiling and evaporating flows. Computers and Fluids, Elsevier, 2016, 128, pp.53-64. <10.1016/j.compfluid.2016.01.004>. <hal-01277179>
Colette Nicoli, Pierre Haldenwang, Bruno Denet. Spray-Flame Dynamics in a Rich Droplet Array. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2016, 96 (2), pp.377-389. Plus de détails...
In a recent numerical paper (Nicoli et al. Combust. Sci. Technol. vol. 186, pp. 103-119; 2014) [1], a model of isobaric flame propagation in lean sprays has been proposed. The initial state of the monodisperse mists was schematized by a system of individual alkane droplets initially located at the nodes of a face-centered 2D-lattice, surrounded by a saturated mixture of alkane and air. In the present study, the previous model is complemented with an original chemical scheme that allows us to study the combustion of rich alkane/air mixtures.
Colette Nicoli, Pierre Haldenwang, Bruno Denet. Spray-Flame Dynamics in a Rich Droplet Array. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2016, 96 (2), pp.377-389. <10.1007/s10494-015-9675-4>. <hal-01282878>
Rachael Aganetti, Aymeric Lamorlette, Guilbert Emilie, Dominique Morvan, G.R. Thorpe. Advection and the self-heating of organic porous media. International Journal of Heat and Mass Transfer, Elsevier, 2016, . Plus de détails...
Self-heating is commonly observed when organic materials such as biosolids, coal, food grains and compost are stockpiled. A convection–diffusion model is presented that accounts for the roles of advection and the transport of oxygen in the self-heating process, as well as the development of an empirical correlation between dimensionless Darcy number, Frank–Kamenetskii parameter and pile aspect ratio, to predict the critical permeability above which thermal runaway can be avoided. It is apparent that the permeability of the stockpile determines the likelihood of the thermal runaway. However, the solids that form a stockpile are poly-disperse and it is essential to determine an effective permeability. This has been achieved using experimental data on biosolids obtained from a wastewater treatment plant in Australia. With this method the model is used to demonstrate how the permeability of a stockpile might be adjusted to reduce the incidence of thermal runaway.
Rachael Aganetti, Aymeric Lamorlette, Guilbert Emilie, Dominique Morvan, G.R. Thorpe. Advection and the self-heating of organic porous media. International Journal of Heat and Mass Transfer, Elsevier, 2016, <10.1016/j.ijheatmasstransfer.2015.11.023>. <hal-01345737>
Journal: International Journal of Heat and Mass Transfer
Damien Furfaro, Richard Saurel. Modeling droplet phase change in the presence of a multi-component gas mixture. Computational and Applied Mathematics, Springer Verlag, 2016, 272 (part.2), pp.518-541. Plus de détails...
Dispersed liquid droplet flows with evaporation and condensation in multi-component gas mixture made of vapor and other gas phase chemical species such as air occur in many engineering applications dealing with two-phase flows. However, existing models are essentially derived for vaporization occurring in sprays combustion. It means that the energy is transferred from a hot gas to the liquid to produce its phase change. This is thus a non-symmetric approach as in some situations the energy is already stored in the liquid phase and flashing occurs as a consequence of pressure drop. In the present paper a droplet mass transfer model is derived and is valid in any situation: evaporation, flashing and condensation. It accounts for: - coupled heat and mass diffusion in the gas phase, - thermodynamics of the multi-component gas mixture, - heat diffusion inside the liquid droplet, enabling consideration of both droplet heating and cooling. These effects are important in evaporating and flashing situations respectively. The resulting model consists in an algebraic non-linear system of three equations giving the interface temperature, the mass flow rate and vapor species concentration at the interface. These interfacial variables enable computation of the mass species, momentum and energy transfer rates appearing in volume averaged two-phase flow models. Computational examples are shown with this mass transfer model embedded in a compressible two-phase flow model of Baer and Nunziato (1986) type.
Damien Furfaro, Richard Saurel. Modeling droplet phase change in the presence of a multi-component gas mixture. Computational and Applied Mathematics, Springer Verlag, 2016, 272 (part.2), pp.518-541. <10.1016/j.amc.2015.02.083>. <hal-01278890>
O Le Métayer, Richard Saurel. The Noble-Abel Stiffened-Gas equation of state. Physics of Fluids, American Institute of Physics, 2016, 28, pp.046102. Plus de détails...
Hyperbolic two-phase flow models have shown excellent ability for the resolution of a wide range of applications ranging from interfacial flows to fluid mixtures with several velocities. These models account for waves propagation (acoustic and convective) and consist in hy-perbolic systems of partial differential equations. In this context, each phase is compressible and needs an appropriate convex equation of state (EOS). The EOS must be simple enough for intensive computations as well as boundary conditions treatment. It must also be accurate , this being challenging with respect to simplicity. In the present approach, each fluid is governed by a novel EOS named 'Noble Abel Stiffened Gas' (NASG), this formulation being a significant improvement of the popular 'Stiffened Gas' (SG) EOS. It is a combination of the so-called 'Noble-Abel' and 'Stiffened Gas' equations of state that adds repulsive effects to the SG formulation. The determination of the various thermodynamic functions and associated coefficients is the aim of this article. We first use thermodynamic considerations to determine the different state functions such as the specific internal energy, enthalpy and entropy. Then we propose to determine the associated coefficients for a liquid in the presence of its vapor. The EOS parameters are determined from experimental saturation curves. Some examples of liquid-vapor fluids are examined and associated parameters are computed with the help of the present method. Comparisons between analytical and experimental saturation curves show very good agreement for wide ranges of temperature for both liquid and vapor.
O Le Métayer, Richard Saurel. The Noble-Abel Stiffened-Gas equation of state. Physics of Fluids, American Institute of Physics, 2016, 28, pp.046102. <10.1063/1.4945981>. <hal-01305974>
Mohamad El Houssami, J.C. Thomas, Aymeric Lamorlette, Dominique Morvan, M. Chaos, et al.. Experimental and numerical studies characterizing the burning dynamics of wildland fuels. Combustion and Flame, Elsevier, 2016, 168, pp.113-126. Plus de détails...
A method to accurately understand the processes controlling the burning behavior of porous wildland fuels is presented using numerical simulations and laboratory experiments. A multiphase approach has been implemented in OpenFOAM, which is based on the FireFOAM solver for large eddy simulations (LES). Conservation equations are averaged in a control volume containing a gas and a solid phase. Drying, pyrolysis, and char oxidation are described by interaction between the two phases. Numerical simulations are compared to laboratory experiments carried out with porous pine needle beds in the FM Global Fire Propagation Apparatus (FPA). These experiments are used to support the use and the development of submodels that represent heat transfer, pyrolysis, gas-phase combustion, and smoldering processes. The model is tested for different bulk densities, two distinct species and two different radiative heat fluxes used to heat up the samples. It has been possible to reproduce mass loss rates, heat release rates, and temperatures that agree with experimental observations, and to highlight the current limitations of the model.
Mohamad El Houssami, J.C. Thomas, Aymeric Lamorlette, Dominique Morvan, M. Chaos, et al.. Experimental and numerical studies characterizing the burning dynamics of wildland fuels. Combustion and Flame, Elsevier, 2016, 168, pp.113-126. <10.1016/j.combustflame.2016.04.004>. <hal-01345741>
Colette Nicoli, Bruno Denet, Pierre Haldenwang. Rich Spray-Flame Propagating through a 2D-Lattice of Alkane Droplets in Air. Combustion and Flame, Elsevier, 2015, 162 (12), pp.4598-4611. Plus de détails...
In a recent numerical paper (Nicoli et al. Combust. Sci. Technol. vol. 186, pp. 103-119; 2014) [1], a model of isobaric flame propagation in lean sprays has been proposed. The initial state of the monodisperse mists was schematized by a system of individual alkane droplets initially located at the nodes of a face-centered 2D-lattice, surrounded by a saturated mixture of alkane and air. In the present study, the previous model is complemented with an original chemical scheme that allows us to study the combustion of rich alkane/air mixtures.
Colette Nicoli, Bruno Denet, Pierre Haldenwang. Rich Spray-Flame Propagating through a 2D-Lattice of Alkane Droplets in Air. Combustion and Flame, Elsevier, 2015, 162 (12), pp.4598-4611. <10.1016/j.combustflame.2015.09.018>. <hal-01255816>
Anthony Randriamampianina, Emilia Crespo del Arco. Inertia–gravity waves in a liquid-filled, differentially heated, rotating annulus. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2015, 782, pp.144- 177. . Plus de détails...
Direct numerical simulations based on high-resolution pseudospectral methods are carried out for detailed investigation into the instabilities arising in a differentially heated, rotating annulus, the baroclinic cavity. Following previous works using air (Randriamampianina et al., J. Fluid Mech., vol. 561, 2006, pp. 359–389), a liquid defined by Prandtl number Pr=16 is considered in order to better understand, via the Prandtl number, the effects of fluid properties on the onset of gravity waves. The computations are particularly aimed at identifying and characterizing the spontaneously emitted small-scale fluctuations occurring simultaneously with the baroclinic waves. These features have been observed as soon as the baroclinic instability sets in. A three-term decomposition is introduced to isolate the fluctuation field from the large-scale baroclinic waves and the time-averaged mean flow. Even though these fluctuations are found to propagate as packets, they remain attached to the background baroclinic waves, locally triggering spatio-temporal chaos, a behaviour not observed with the air-filled cavity. The properties of these features are analysed and discussed in the context of linear theory. Based on the Richardson number criterion, the characteristics of the generation mechanism are consistent with a localized instability of the shear zonal flow, invoking resonant over-reflection.
Anthony Randriamampianina, Emilia Crespo del Arco. Inertia–gravity waves in a liquid-filled, differentially heated, rotating annulus. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2015, 782, pp.144- 177. <http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9992050&fulltextType=RA&fileId=S0022112015005224>. <10.1017/jfm.2015.522 >. <hal-01230540>
Guillaume Chiavassa, M.C. Martí, P. Mulet. Hybrid WENO schemes for polydisperse sedimentation models. International Journal of Computer Mathematics, Taylor & Francis, 2015, pp.1-17. Plus de détails...
Polydisperse sedimentation models can be described by a strongly coupled system of conservation laws for the concentration of each species of solids. Typical solutions for the sedimentation model considered for batch settling in a column include stationary kinematic shocks separating layers of sediment of different composition. This phenomenon, known as segregation of species, is a specially demanding task for numerical simulation due to the need of accurate numerical simulations. Very high-order accurate solutions can be constructed by incorporating characteristic information, available due to the hyperbolicity analysis made in Donat and Mulet [A secular equation for the Jacobian matrix of certain multispecies kinematic flow models, Numer. Methods Partial Differential Equations 26 (2010), pp. 159–175.] But characteristic-based schemes, see Bürger et al. [On the implementation of WENO schemes for a class of polydisperse sedimentation models, J. Comput. Phys. 230 (2011), pp. 2322–2344], are very expensive in terms of computational time, since characteristic information is not readily available, and they are not really necessary in constant areas, where a less complex method can obtain similar results. With this idea in mind, in this paper we develop a hybrid finite difference WENO scheme that only uses the characteristic information of the Jacobian matrix of the system in those regions where singularities exist or are starting to develop, while it uses a component-wise approximation of the scheme in smooth regions. We perform some experiments showing the computational gains that can be achieved by this strategy.
Guillaume Chiavassa, M.C. Martí, P. Mulet. Hybrid WENO schemes for polydisperse sedimentation models. International Journal of Computer Mathematics, Taylor & Francis, 2015, pp.1-17. <10.1080/00207160.2015.1075985>. <hal-01297719>
Journal: International Journal of Computer Mathematics
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stephane Viazzo, Michael Le Bars. Velocity and temperature measurements in a turbulent water-filled Taylor–Couette–Poiseuille system. International Journal of Thermal Sciences, Elsevier, 2015, 90, pp. 238-247. Plus de détails...
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stephane Viazzo, Michael Le Bars. Velocity and temperature measurements in a turbulent water-filled Taylor–Couette–Poiseuille system. International Journal of Thermal Sciences, Elsevier, 2015, 90, pp. 238-247. <hal-01308638>
Journal: International Journal of Thermal Sciences
Damien Furfaro, Richard Saurel. A simple HLLC-type Riemann solver for compressible non-equilibrium two-phase flows. Computers and Fluids, Elsevier, 2015, 111, pp.159-178. Plus de détails...
A simple, robust and accurate HLLC-type Riemann solver for two-phase 7-equation type models is built. It involves 4 waves per phase, i.e. the three conventional right- and left-facing and contact waves, augmented by an extra “interfacial” wave. Inspired by the Discrete Equations Method (Abgrall and Saurel, 2003), this wave speed (uIuI) is assumed function only of the piecewise constant initial data. Therefore it is computed easily from these initial states. The same is done for the interfacial pressure PIPI. Interfacial variables uIuI and PIPI are thus local constants in the Riemann problem. Thanks to this property there is no difficulty to express the non-conservative system of partial differential equations in local conservative form. With the conventional HLLC wave speed estimates and the extra interfacial speed uIuI, the four-waves Riemann problem for each phase is solved following the same strategy as in Toro et al. (1994) for the Euler equations. As uIuI and PIPI are functions only of the Riemann problem initial data, the two-phase Riemann problem consists in two independent Riemann problems with 4 waves only. Moreover, it is shown that these solvers are entropy producing. The method is easy to code and very robust. Its accuracy is validated against exact solutions as well as experimental data.
Damien Furfaro, Richard Saurel. A simple HLLC-type Riemann solver for compressible non-equilibrium two-phase flows. Computers and Fluids, Elsevier, 2015, 111, pp.159-178. <10.1016/j.compfluid.2015.01.016>. <hal-01278892>
Gustavo Henndel Lopes, Nelson Ibaseta, Pierrette Guichardon, Pierre Haldenwang. Predicting Permeate Fluxes and Rejection Rates in Reverse Osmosis and Tight-Nanofiltration Processes. Chemical Engineering and Technology, Wiley-VCH Verlag, 2015, 38 (4), pp.585-594. Plus de détails...
The performance of reverse osmosis and tight nanofiltration with flat-sheet membranes can be predicted accurately. The proposed numerical model solves the local momentum and mass conservation equations in the module's feed channel with solution-diffusion boundary conditions. Both qualitative and quantitative predictions of the permeate flux and of the rejection rate are obtained with an accuracy depending on the limitations of the solution-diffusion model for describing membrane mass transport and on the value of solute permeability. As an extension of the applications to plate-and-frame modules, the ability to describe the performance of processes carried out with spiral-wound modules is also tested with own desalination experiments and with data from the literature.
Gustavo Henndel Lopes, Nelson Ibaseta, Pierrette Guichardon, Pierre Haldenwang. Predicting Permeate Fluxes and Rejection Rates in Reverse Osmosis and Tight-Nanofiltration Processes. Chemical Engineering and Technology, Wiley-VCH Verlag, 2015, 38 (4), pp.585-594. <10.1002/ceat.201400654>. <hal-01135689>
Aymeric Lamorlette, Mohamad El Houssami, Jan C. Thomas, Albert Simeoni, Dominique Morvan. A dimensional analysis of forest fuel layer ignition model: Application to the ignition of pine needle litters. Journal of Fire Sciences, SAGE Publications, 2015, pp.NC. Plus de détails...
This paper deals with the physical modelling of forest fuel layer ignition. A model based on momentum, fluid and solid phase energy equations is written for a fuel layer and a dimensional analysis is performed. This analysis allows to enlighten two relevant dimensionless groups regarding the dimensionless time to ignition of a fuel layer and also provides a suited scaling for the fluid velocity inside the fuel layer during ignition. A correlation for the time to ignition is then fitted on experimental data obtained using a FM-Global Fire Propagation Apparatus (FPA) for different pine species with a closed basket. A good agreement is found, emphasizing the relevance of the dimensionless groups and the thermally thick behaviour of the solid particles during the ignition process under incident radiant heat flux as low as 8 − 12kW.m −2 .
Aymeric Lamorlette, Mohamad El Houssami, Jan C. Thomas, Albert Simeoni, Dominique Morvan. A dimensional analysis of forest fuel layer ignition model: Application to the ignition of pine needle litters. Journal of Fire Sciences, SAGE Publications, 2015, pp.NC. <10.1177/ToBeAssigned>. <hal-01157866>
Dominique Morvan. Numerical study of the behaviour of a surface fire propagating through a firebreak built in a Mediterranean shrub layer. Fire Safety Journal, Elsevier, 2015, 71 (7), pp.34-48. Plus de détails...
The efficiency of a firebreak, built in a shrubland has been studied numerically using a multiphase physical model. The physical mechanisms governing the propagation of the surface fire and the consequences upon the temperature signal and the radiative heat flux received by a target located at 1 m above the ground level, have been firstly studied before positioning the firebreak. The role played by the flame and the recirculation of hot gases to the ignition of unburned fuel (especially the dry grass) ahead of the fire front have been clearly identified. Four values of the firebreak width LC (ranged between 5 and 20 m) and 3 values of wind velocities (ranged between 1 and 8 m/s) have been tested. The simulations show that above a threshold value of this parameter, even if a small amount of the fuel located on the opposite side of the firebreak was ignited, the released energy was not sufficient to sustain the propagation of the surface fire after crossing the firebreak.
Dominique Morvan. Numerical study of the behaviour of a surface fire propagating through a firebreak built in a Mediterranean shrub layer. Fire Safety Journal, Elsevier, 2015, 71 (7), pp.34-48. <10.1016/j.firesaf.2014.11.012>. <hal-01297711>
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stéphane Viazzo, Michel Lebars. Velocity and temperature measurements in a turbulent water-filled Taylor-Couette-Poiseuille system. International Journal of Thermal Sciences, Elsevier, 2015. Plus de détails...
Motivated by the difficulties encountered by engineers to cool down the rotating shafts of industrial machines, the present work investigates the heat and mass transfers in the rotor-stator gap of a Taylor–Couette system with an axial water flow characterized by an aspect ratio Γ = 50 and a radius ratio η = 8/9. Extensive velocity and temperature measurements have been performed on an experimental set-up for a wide range of the flow parameters: the axial Reynolds number Re and the Taylor number Ta reach the values 1.12 × 104 and 7.9 × 107 respectively. In particular, coherent structures close to the rotating wall were measured by Stereo Particle Image Velocimetry. A correlation for the Nusselt number Nu on the rotating wall is finally provided against the axial Reynolds, Taylor and Prandtl numbers. Nu is proportional to the Taylor number to the power ∼0.13 close to the exponent 1/7 highlighted by an analytical model. This small exponent traduces the control of heat transfers by the rotating viscous layer and thus may explain the difficulty met by engineers to develop strategies for the effective cooling of such rotating apparatus.
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stéphane Viazzo, Michel Lebars. Velocity and temperature measurements in a turbulent water-filled Taylor-Couette-Poiseuille system. International Journal of Thermal Sciences, Elsevier, 2015. <hal-01467719>
Journal: International Journal of Thermal Sciences
Bouchra Bensiali, Guillaume Chiavassa, Jacques Liandrat. Penalization of Robin boundary conditions. Applied Numerical Mathematics, Elsevier, 2015, pp.134-152. Plus de détails...
This paper is devoted to the mathematical analysis of a method based on fictitious domain approach. Boundary conditions of Robin type (also known as Fourier boundary conditions) are enforced using a penalization method. A complete description of the method and a full analysis are provided for univariate elliptic and parabolic problems using finite difference approximation. Numerical evidence of the predicted estimations is provided as well as numerical results for a nonlinear problem and a first extension of the method in the bivariate situation is proposed.
Bouchra Bensiali, Guillaume Chiavassa, Jacques Liandrat. Penalization of Robin boundary conditions. Applied Numerical Mathematics, Elsevier, 2015, pp.134-152. <hal-01266091>
Aymeric Lamorlette, Fabien Candelier. Thermal behavior of solid particles at ignition: Theoretical limit between thermally thick and thin solids. International Journal of Heat and Mass Transfer, Elsevier, 2015, pp.117-122. Plus de détails...
This paper deals with thermal behaviors of solid particles at ignition in attempting to theoretically delineate transition between thermally thick and thin behavior when a solid target is exposed to a radiant heat flux. In order to evaluate classical asymptotic relation accuracy and limiting range, models are developed for finite-depth target in both Cartesian and cylindrical coordinates, allowing to enhance asymptotic relations. Comparison between finite-depth target solutions and asymptotic solutions finally provides a mapping which allows the suited relation for ignition time calculation to be determined, regarding ignition conditions. This mapping then suggests some interesting consequences on forest fuel ignition and fire propagation modeling, since asymptotic models seem to overlap on large regions.
Aymeric Lamorlette, Fabien Candelier. Thermal behavior of solid particles at ignition: Theoretical limit between thermally thick and thin solids. International Journal of Heat and Mass Transfer, Elsevier, 2015, pp.117-122. <10.1016/j.ijheatmasstransfer.2014.11.037>. <hal-01096409>
Journal: International Journal of Heat and Mass Transfer
Richard Saurel, Sebastien Le Martelot, Robert Tosello, Emmanuel Lapebie. Symmetric model of compressible granular mixtures with permeable interfaces. Physics of Fluids, American Institute of Physics, 2014, 26 (12), . Plus de détails...
Compressible granular materials are involved in many applications, some of them being related to energetic porous media. Gas permeation effects are important during their compaction stage, as well as their eventual chemical decomposition. Also, many situations involve porous media separated from pure fluids through two-phase interfaces. It is thus important to develop theoretical and numerical formulations to deal with granular materials in the presence of both two-phase interfaces and gas permeation effects. Similar topic was addressed for fluid mixtures and interfaces with the Discrete Equations Method (DEM) [R. Abgrall and R. Saurel, ``Discrete equations for physical and numerical compressible multiphase mixtures,''J. Comput. Phys. 186 (2), 361-396 (2003)] but it seemed impossible to extend this approach to granular media as intergranular stress [K. K. Kuo, V. Yang, and B. B. Moore, ``Intragranular stress, particle-wall friction and speed of sound in granular propellant beds,'' J. Ballist. 4 (1), 697-730 (1980)] and associated configuration energy [J. B. Bdzil, R. Menikoff, S. F. Son, A. K. Kapila, and D. S. Stewart, `` Two-phase modeling of deflagration-to-detonation transition in granular materials: A critical examination of modeling issues,'' Phys. Fluids 11, 378 (1999)] were present with significant effects. An approach to deal with fluid-porous media interfaces was derived in Saurel et al. [''Modelling dynamic and irreversible powder compaction,'' J. Fluid Mech. 664, 348-396 (2010)] but its validity was restricted to weak velocity disequilibrium only. Thanks to a deeper analysis, the DEM is successfully extended to granular media modelling in the present paper. It results in an enhanced version of the Baer and Nunziato [''A two-phase mixture theory for the deflagration-to-detonation transition (DDT) in reactive granular materials,'' Int. J. Multiphase Flow 12 (6), 861-889 (1986)] model as symmetry of the formulation is now preserved. Several computational examples are shown to validate and illustrate method's capabilities. (C) 2014 AIP Publishing LLC.
Richard Saurel, Sebastien Le Martelot, Robert Tosello, Emmanuel Lapebie. Symmetric model of compressible granular mixtures with permeable interfaces. Physics of Fluids, American Institute of Physics, 2014, 26 (12), <10.1063/1.4903259>. <hal-01459320>
Gustavo Henndel Lopes, Pierrette Guichardon, Nelson Ibaseta, Pierre Haldenwang. L’eau, ressource rare ? Gros plan sur le procédé de dessalement par membranes d’osmose inverse. L'Actualité Chimique, 2014, N° thématique: La chimie et la ville de demain Colloque Recherche de la Fédération Gay-Lussac, Paris, 4-6 décembre 2013, 390, pp.85-87. Plus de détails...
Le procédé d’osmose inverse s’impose aujourd'hui dans la production d’eau douce par dessalement. Des avancées en matière de prédiction des performances de ce procédé s’avèrent précieuses dans l’optimisation rapide et peu coûteuse des conditions de fonctionnement. L’interaction entre les propriétés de la membrane et les phénomènes prépondérants (polarisation de concentration, pression osmotique...) constitue un problème scientifiquement complexe, traité dans cette étude via une approche modélisation numérique-simulation-expérimentation, une question centrale pour le génie des procédés.
Gustavo Henndel Lopes, Pierrette Guichardon, Nelson Ibaseta, Pierre Haldenwang. L’eau, ressource rare ? Gros plan sur le procédé de dessalement par membranes d’osmose inverse. L'Actualité Chimique, 2014, N° thématique: La chimie et la ville de demain Colloque Recherche de la Fédération Gay-Lussac, Paris, 4-6 décembre 2013, 390, pp.85-87. <http://www.lactualitechimique.org/L-eau-ressource-rare-Gros-plan-sur-le-procede-de>. <hal-01116186>
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. Wave simulation in 2D heterogeneous transversely isotropic porous media ă with fractional attenuation: A Cartesian grid approach. Journal of Computational Physics, Elsevier, 2014, 275, pp.118-142. Plus de détails...
A time-domain numerical modeling of transversely isotropic Biot ă poroelastic waves is proposed in two dimensions. The viscous dissipation ă occurring in the pores is described using the dynamic permeability model ă developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in ă the Biot-JKD model are proportional to the square root of the frequency. ă In the time-domain, these coefficients introduce shifted fractional ă derivatives of order 1/2, involving a convolution product. Based on a ă diffusive representation, the convolution kernel is replaced by a finite ă number of memory variables that satisfy local-in-time ordinary ă differential equations, resulting in the Biot-DA (diffusive ă approximation) model. The properties of both the Biot-JKD and the ă Biot-DA models are analyzed: hyperbolicity, decrease of energy, ă dispersion. To determine the coefficients of the diffusive ă approximation, two approaches are analyzed: Gaussian quadratures and ă optimization methods in the frequency range of interest. The nonlinear ă optimization is shown to be the better way of determination. A splitting ă strategy is then applied to approximate numerically the Biot-DA ă equations. The propagative part is discretized using a fourth-order ADER ă scheme on a Cartesian grid, whereas the diffusive part is solved ă exactly. An immersed interface method is implemented to take into ă account heterogeneous media on a Cartesian grid and to discretize the ă jump conditions at interfaces. Numerical experiments are presented. ă Comparisons with analytical solutions show the efficiency and the ă accuracy of the approach, and some numerical experiments are performed ă to investigate wave phenomena in complex media, such as multiple ă scattering across a set of random scatterers. (C) 2014 Elsevier Inc. All ă rights reserved.
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. Wave simulation in 2D heterogeneous transversely isotropic porous media ă with fractional attenuation: A Cartesian grid approach. Journal of Computational Physics, Elsevier, 2014, 275, pp.118-142. <10.1016/j.jcp.2014.07.002>. <hal-01464704>
Colette Nicoli, Bruno Denet, Pierre Haldenwang. Lean flame dynamics through a 2D lattice of alkane droplets in air. Combustion Science and Technology, Taylor & Francis, 2014, 186 (2), pp.103-119. Plus de détails...
Flame propagation along a 1-D array or through a 2D-lattice of fuel droplets has long been suggested to schematize spray-flames spreading in a two-phase premixture. The present numerical work considers the fresh aerosol as a system of individual alkane droplets initially located at the nodes of a face-centered 2D-lattice, surrounded by a variable mixture of alkane and air, in which the droplets can move. The main parameters of the study are s, the lattice path, and phi_ L , the liquid loading, which are both varied, whereas phi_T , the overall equivalence ratio, is maintained lean ( phi_T = 0.85). Main results are as follows: (a) For a large lattice path (or when the droplets are large enough), spreading occurs in two stages: a short time of combustion followed by a long time lag of vaporization and a classical triple flame (with a very short rich wing) spreads around the droplets; (b) spray-flame speed decreases as liquid loading increases; (c) an elementary model invoking both propagation stages allows us to interpret flame speed as a function of the sole parameter s × phi_ L ; (d) when the lattice path shortens, the spray-flame exhibits a pattern that continuously goes from this situation to the plane flame front.
Colette Nicoli, Bruno Denet, Pierre Haldenwang. Lean flame dynamics through a 2D lattice of alkane droplets in air. Combustion Science and Technology, Taylor & Francis, 2014, 186 (2), pp.103-119. <hal-00935131>
B. Bernales, Pierre Haldenwang. Laminar flow analysis in a pipe with locally pressure-dependent leakage through the wall. European Journal of Mechanics - B/Fluids, Elsevier, 2014, 43, pp.100-109. Plus de détails...
The paper analyzes the problem of the leaky pipe (or a porous-walled pipe), namely the laminar flow of a pure fluid that takes place in a pipe, the wall of which is composed of a porous material. This configuration is inspired by some watering systems or by the cross-flow (or tangential) filtration configuration for membrane separation or capillary flow. It assumes that the leakage through the wall (or permeate) results from the pressure difference between both sides of the pipe wall, and is here modeled by the Starling-Darcy law. The inner pressure along the pipe behaves accordingly with two competitive features: the viscous pressure drop competing against the pressure increase due to pipe axial flow deceleration. It is long known that both features compensate at a critical value, R-t(iso), of the transverse Reynolds number R-t (based on transpiration velocity); this corresponds to the only situation where the pressure remains uniform along the channel. The case with uniform leakage known as Berman flow possesses a similarity solution due to Yuan and Finkelstein (1956) [2] for the pipe configuration. The paper is aimed at extending the latter study to a non-uniform leakage depending linearly on local pressure. First, the similarity solution is revisited. Its expansion in a series of R-t allows us to propose a hierarchy of new ordinary differential equations (ODEs), that extend to small or moderate R-t the linear ODE proposed for the limit case R-t = 0 by Regirer (1960) [25]. As by-products, we propose approximate analytical solutions that solve the problem of the leaking pipe with increasing accuracy in the weakly non-linear case (WNL) (i.e. for small and moderate R-t). Finally, the validity of ODEs and WNL solutions is numerically checked with respect to flow simulations in the Prandtl approximation. (C) 2013 Elsevier Masson SAS. All rights reserved.
B. Bernales, Pierre Haldenwang. Laminar flow analysis in a pipe with locally pressure-dependent leakage through the wall. European Journal of Mechanics - B/Fluids, Elsevier, 2014, 43, pp.100-109. <10.1016/j.euromechflu.2013.07.006>. <hal-01053307>
Anthony Randriamampianina, Emilia Crespo del Arco. High resolution method for direct numerical simulation of the instability and transition in a baroclinic cavity. Thomas von Larcher, Paul D. Williams. Modelling atmospheric and oceanic flows: insights from laboratory experiments and numerical simulations, Wiley, chapter V.2, 2014, American Geophysical Union Series, 978-1-118-85593-5. Plus de détails...
Anthony Randriamampianina, Emilia Crespo del Arco. High resolution method for direct numerical simulation of the instability and transition in a baroclinic cavity. Thomas von Larcher, Paul D. Williams. Modelling atmospheric and oceanic flows: insights from laboratory experiments and numerical simulations, Wiley, chapter V.2, 2014, American Geophysical Union Series, 978-1-118-85593-5. <hal-00993357>
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. Wave simulation in 2D heterogeneous transversely isotropic porous media with fractional attenuation: a Cartesian grid approach. Journal of Computational Physics, Elsevier, 2014, 275, pp.118-142. Plus de détails...
A time-domain numerical modeling of transversely isotropic Biot poroelastic waves is proposed in two dimensions. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD model are proportional to the square root of the frequency. In the time-domain, these coefficients introduce shifted fractional derivatives of order 1/21/2, involving a convolution product. Based on a diffusive representation, the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations, resulting in the Biot-DA (diffusive approximation) model. The properties of both the Biot-JKD and the Biot-DA model are analyzed: hyperbolicity, decrease of energy, dispersion. To determine the coefficients of the diffusive approximation, two approaches are analyzed: Gaussian quadratures and optimization methods in the frequency range of interest. The nonlinear optimization is shown to be the better way of determination. A splitting strategy is then applied to approximate numerically the Biot-DA equations. The propagative part is discretized using a fourth-order ADER scheme on a Cartesian grid, whereas the diffusive part is solved exactly. An immersed interface method is implemented to take into account heterogeneous media on a Cartesian grid and to discretize the jump conditions at interfaces. Numerical experiments are presented. Comparisons with analytical solutions show the efficiency and the accuracy of the approach, and some numerical experiments are performed to investigate wave phenomena in complex media, such as multiple scattering across a set of random scatterers.
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. Wave simulation in 2D heterogeneous transversely isotropic porous media with fractional attenuation: a Cartesian grid approach. Journal of Computational Physics, Elsevier, 2014, 275, pp.118-142. <hal-00949686v2>
Dominique Morvan. Wind effects, unsteady behaviors, and regimes of propagation of surface fires in open field. Combustion Science and Technology, Taylor & Francis, 2014, 186 (7), pp.869-888. Plus de détails...
The subject of this article concerns the unsteady effects (fire intensity, wind) upon the propagation and, more generally, the behavior of surface fires in open fields. The study focused on two sources of unsteadiness: the first one resulting from the regime of propagation (wind driven or plume dominated), which can affect greatly the behavior of the flame front and consequently the fire intensity, the second one resulting from the wind gusts associated with the conditions of flow of wind in real conditions. The study was based on numerical simulations, using a multiphase formulation, and on spectral analysis of the time evolution of the fire line intensity. The calculations were performed in 2D for a homogeneous vegetation layer (grassland) and for a large interval of wind conditions (10 m open wind velocity U10 ranged between 1 m/s and 25 m/s). The results have highlighted the link between the unsteady character of flame front behavior and the regime of propagation (plume dominated, wind driven). A particular interest was focused on the role played by two potential sources of instabilities, namely the Kelvin-Helmholtz instability (wind effects) and the thermo-convective instability (plume effects), upon the behavior of fires. A second set of simulations has been carried out using unsteady wind conditions, reproduced using sinusoidal boundary conditions for the streamwise velocity, with a frequency ranging between 0.5 Hz and 3 Hz.
Dominique Morvan. Wind effects, unsteady behaviors, and regimes of propagation of surface fires in open field. Combustion Science and Technology, Taylor & Francis, 2014, 186 (7), pp.869-888. <10.1080/00102202.2014.885961>. <hal-01049769>
Aymeric Lamorlette. Analytical modeling of solid material ignition under a radiant heat flux coming from a spreading fire front. Journal of Thermal Science and Engineering Applications, 2014, 6 (4), pp.044501. Plus de détails...
This study aims at characterizing ignition of solid targets exposed to spreading fire fronts. In order to model radiant heat fluxes on targets in a realistic way, polynomial heat fluxes are chosen. Analytical solutions for the solid surface temperature evolution regarding different time-varying heat fluxes are discussed for high thermal inertia solids using a mathematical formalism, which allows for the methodology to be extended to the case of low thermal inertia. This formulation also allows calculation of ignition times for more realistic time-dependent fluxes than previous studies on the topic, providing a more general solution to the problem of solid material ignition. Polynomial coefficients are then obtained fitting heat flux coming from absorbing-emitting flames. A characterization of solid material ignition times regarding fire front rate of spread (ROS) is finally performed, showing the need to accurately model heat flux variations in ignition time calculations.
Aymeric Lamorlette. Analytical modeling of solid material ignition under a radiant heat flux coming from a spreading fire front. Journal of Thermal Science and Engineering Applications, 2014, 6 (4), pp.044501. <10.1115/1.4028204>. <hal-01059491>
Journal: Journal of Thermal Science and Engineering Applications
Aymeric Lamorlette. Quantification of ignition time uncertainty based on the classical ignition theory and Fourier analysis. Comptes Rendus Mécanique, Elsevier Masson, 2014, 342 (8), pp.459 - 465. Plus de détails...
This study aims at modeling the effect of incoming heat flux fluctuations, on solid material ignition. In order to propose a general methodology based on the classical ignition theory that can be applied to any kind of solid target, kernels accounting for the target temperature response regarding an incoming heat flux are considered for thermally thick and thin solids with low or high thermal inertia. A Fourier decomposition of the incoming heat flux is then used to calculate the target response to harmonic heat fluxes. Finally, effects of harmonic fluctuations on ignition are discussed based on the previous analytical results, allowing to discriminate situations where ignition time is expected to be rather predictable from situations where ignition time is expected to be less predictable thanks to an uncertainty quantification of the ignition time. To cite this article: Aymeric Lamorlette, C. R. Mecanique 333 (2005).
Aymeric Lamorlette. Quantification of ignition time uncertainty based on the classical ignition theory and Fourier analysis. Comptes Rendus Mécanique, Elsevier Masson, 2014, 342 (8), pp.459 - 465. <10.1016/j.crme.2014.06.002>. <hal-01096403>
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. A time-domain numerical modeling of two-dimensional wave propagation in ă porous media with frequency-dependent dynamic permeability. Journal of the Acoustical Society of America, Acoustical Society of America, 2013, 134 (6, 2, SI), pp.4610-4623. Plus de détails...
An explicit finite-difference scheme is presented for solving the ă two-dimensional Biot equations of poroelasticity across the full range ă of frequencies. The key difficulty is to discretize the ă Johnson-Koplik-Dashen (JKD) model which describes the viscous ă dissipations in the pores. Indeed, the time-domain version of Biot-JKD ă model involves order 1/2 fractional derivatives which amount to a time ă convolution product. To avoid storing the past values of the solution, a ă diffusive representation of fractional derivatives is used: The ă convolution kernel is replaced by a finite number of memory variables ă that satisfy local-in-time ordinary differential equations. The ă coefficients of the diffusive representation follow from an optimization ă procedure of the dispersion relation. Then, various methods of ă scientific computing are applied: The propagative part of the equations ă is discretized using a fourth-order finite-difference scheme, whereas ă the diffusive part is solved exactly. An immersed interface method is ă implemented to discretize the geometry on a Cartesian grid, and also to ă discretize the jump conditions at interfaces. Numerical experiments are ă proposed in various realistic configurations. (C) 2013 Acoustical ă Society of America.
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. A time-domain numerical modeling of two-dimensional wave propagation in ă porous media with frequency-dependent dynamic permeability. Journal of the Acoustical Society of America, Acoustical Society of America, 2013, 134 (6, 2, SI), pp.4610-4623. <10.1121/1.4824832>. <hal-01464730>
Journal: Journal of the Acoustical Society of America
Sébastien Poncet, Thien Nguyen, Souad Harmand, Julien Pellé, Riccardo Da Soghe, et al.. Turbulent impinging jet flow into an unshrouded rotor-stator system: Hydrodynamics and heat transfer. International Journal of Heat and Fluid Flow, Elsevier, 2013, 44, pp.719-734. Plus de détails...
New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k-w SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor-stator system. The cavity is characterized by a dimensionless spacing interval G=0.02 and a low aspect ratio for the jet e/D=0.25. Jet Reynolds numbers ranging from 17200 to 43000 and rotational Reynolds numbers between 33000 and 532000 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotation-dominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k-wSST model overestimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.
Sébastien Poncet, Thien Nguyen, Souad Harmand, Julien Pellé, Riccardo Da Soghe, et al.. Turbulent impinging jet flow into an unshrouded rotor-stator system: Hydrodynamics and heat transfer. International Journal of Heat and Fluid Flow, Elsevier, 2013, 44, pp.719-734. <10.1016/j.ijheatfluidflow.2013.10.001>. <hal-00976669>
Journal: International Journal of Heat and Fluid Flow
Sébastien Poncet, Stéphane Viazzo, Adrien Aubert, Riccardo Da Soghe, Cosimo Bianchini. Turbulent Couette-Taylor flows with endwall effects: a numerical benchmark. International Journal of Heat and Fluid Flow, Elsevier, 2013, 44, pp.229-238. Plus de détails...
The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette-Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Rea, the exponent a = 1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k-w SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement.
Sébastien Poncet, Stéphane Viazzo, Adrien Aubert, Riccardo Da Soghe, Cosimo Bianchini. Turbulent Couette-Taylor flows with endwall effects: a numerical benchmark. International Journal of Heat and Fluid Flow, Elsevier, 2013, 44, pp.229-238. <10.1016/j.ijheatfluidflow.2013.05.018>. <hal-00975636>
Journal: International Journal of Heat and Fluid Flow
Djilali Ameur, Isabelle Raspo. Numerical Simulation of the Poiseuille-Rayleigh-Bénard Instability for a Supercritical Fluid in a Mini-channel. Computational Thermal Sciences, 2013, 5 (2), pp.107-118. Plus de détails...
The Poiseuille-Rayleigh-Bénard problem, involving the onset of thermoconvective structures in channels heated from below, was the subject of many theoretical, numerical and experimental studies for incompressible flows or perfect gas. However, to the authors' knowledge, this problem was never studied for supercritical fluids. The objective of this paper is to study the influence of the specific properties of such fluids on thermoconvective instability phenomena compared with those observed in the perfect gas case. The effect of the distance to the critical point is also investigated. The numerical approach used is based on the Navier-Stokes equations in the framework of the low Mach number approximation.
Djilali Ameur, Isabelle Raspo. Numerical Simulation of the Poiseuille-Rayleigh-Bénard Instability for a Supercritical Fluid in a Mini-channel. Computational Thermal Sciences, 2013, 5 (2), pp.107-118. <10.1615/ComputThermalScien.2013006169>. <hal-00834707>
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. Biot-JKD model: simulation of 1D transient poroelastic waves with fractional derivatives. Journal of Computational Physics, Elsevier, 2013, 237, pp.1-20. Plus de détails...
A time-domain numerical modeling of Biot poroelastic waves is presented. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD model are proportional to the square root of the frequency: in the time-domain, these coefficients introduce order 1/2 shifted fractional derivatives involving a convolution product. Based on a diffusive representation, the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations. Thanks to the dispersion relation, the coefficients in the diffusive representation are obtained by performing an optimization procedure in the frequency range of interest. A splitting strategy is then applied numerically: the propagative part of Biot-JKD equations is discretized using a fourth-order ADER scheme on a Cartesian grid, whereas the diffusive part is solved exactly. Comparisons with analytical solutions show the efficiency and the accuracy of this approach.
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. Biot-JKD model: simulation of 1D transient poroelastic waves with fractional derivatives. Journal of Computational Physics, Elsevier, 2013, 237, pp.1-20. <10.1016/j.jcp.2012.12.003>. <hal-00713127v2>
Dominique Morvan. Numerical study of the effect of fuel moisture content (FMC) upon the propagation of a surface fire on a flat terrain. Fire Safety Journal, Elsevier, 2013, 58, pp.121-131. Plus de détails...
This paper was devoted to clarify and evaluate how fuel moisture content (FMC) characterising a homogeneous vegetation layer (grass or shrubs), can affect the behaviour of surface fire. The approach used in this study was based on numerical simulations performed using a detailed fire physical model. The numerical results were analysed in terms of fire residence time, fire front depth, mass loss rate and rate of spread (ROS). Two windy conditions (calm and weak) were studied to evaluate the decay of the rate of spread (ROS) resulting from an increase of the fuel moisture content. The effect of wind velocity upon marginal burning conditions was also analysed. The numerical results were compared with empirical data of the literature.
Dominique Morvan. Numerical study of the effect of fuel moisture content (FMC) upon the propagation of a surface fire on a flat terrain. Fire Safety Journal, Elsevier, 2013, 58, pp.121-131. <10.1016/j.firesaf.2013.01.010>. <hal-01030813>
Journal: Fire Safety Journal
Date de publication: 01-01-2013
Auteurs:
Dominique Morvan
2013
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. A time-domain numerical modeling of two-dimensional wave propagation in porous media with frequency-dependent dynamic permeability. Journal of the Acoustical Society of America, Acoustical Society of America, 2013, 134 (6), pp.4610-4623. Plus de détails...
An explicit finite-difference scheme is presented for solving the two-dimensional Biot equations of poroelasticity across the full range of frequencies. The key difficulty is to discretize the Johnson-Koplik-Dashen (JKD) model which describes the viscous dissipations in the pores. Indeed, the time-domain version of Biot-JKD model involves order 1/2 fractional derivatives which amounts to a time convolution product. To avoid storing the past values of the solution, a diffusive representation of fractional derivatives is used: the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations. The coefficients of the diffusive representation follow from an optimization procedure of the dispersion relation. Then, various methods of scientific computing are applied: the propagative part of the equations is discretized using a fourth-order finite-difference scheme, whereas the diffusive part is solved exactly. An immersed interface method is implemented to discretize the geometry on a Cartesian grid, and also to discretize the jump conditions at interfaces. Numerical experiments are proposed in various realistic configurations.
Emilie Blanc, Guillaume Chiavassa, Bruno Lombard. A time-domain numerical modeling of two-dimensional wave propagation in porous media with frequency-dependent dynamic permeability. Journal of the Acoustical Society of America, Acoustical Society of America, 2013, 134 (6), pp.4610-4623. <hal-00736757>
Journal: Journal of the Acoustical Society of America
K. Gavrilov, Dominique Morvan, Gilbert Accary, Dimitry Lyubimov, Sofiane Meradji. Numerical simulation of coherent turbulent structures and of passive scalar dispersion in a canopy sub-layer. Computers and Fluids, Elsevier, 2013, 78, pp.54-62. Plus de détails...
This study deals with the problem of turbulent atmospheric boundary-layer flow over a forest canopy. Numerous previous works showed that this flow presents more similarities with a mixing-layer flow than with the standard boundary-layer flow. In this paper, this problem was studied for homogeneous canopies, using large eddy simulation (LES). The numerical results reproduced correctly the various steps of development of this flow: the appearance of a first generation of coherent structures resulting from the development of a primary Kelvin-Helmholtz instability, the reorganization of these structures, by vortex pairing and kinking, the development of a secondary instability and the formation of horseshoe vortices. Then, the process of transport of a passive scalar from a forest canopy into a clear atmosphere was studied in two cases, i.e., when the passive scalar concentration at the surface foliage is either constant or time-varying. Even though this small difference has little influence on the concentration patterns, the results showed that it can significantly affect the concentration magnitude as well as the dynamics of the total concentration in the atmosphere.
K. Gavrilov, Dominique Morvan, Gilbert Accary, Dimitry Lyubimov, Sofiane Meradji. Numerical simulation of coherent turbulent structures and of passive scalar dispersion in a canopy sub-layer. Computers and Fluids, Elsevier, 2013, 78, pp.54-62. <10.1016/j.compfluid.2012.08.021>. <hal-01030794>
Konstantin Gavrilov, Dmitri Lyubimov, Dominique Morvan, Gilbert Accary, Sofiane Meradji. Admixture transport model for atmospheric boundary layer flow over forest canopy. N. I. Lobachevsky Bulletin de l'Université de Ninji-Novgorod, 1 (3), pp.244-252, 2013, La Modélisation Mathématique: Contôle Optimal. Plus de détails...
Konstantin Gavrilov, Dmitri Lyubimov, Dominique Morvan, Gilbert Accary, Sofiane Meradji. Admixture transport model for atmospheric boundary layer flow over forest canopy. N. I. Lobachevsky Bulletin de l'Université de Ninji-Novgorod, 1 (3), pp.244-252, 2013, La Modélisation Mathématique: Contôle Optimal. <hal-01313312>
Date de publication: 01-01-2013
Auteurs:
Konstantin Gavrilov
Dmitri Lyubimov
Dominique Morvan
Gilbert Accary
Sofiane Meradji
2013
Anthony Randriamampianina. Inertia gravity waves characteristics within a baroclinic cavity. Comptes Rendus Mécanique, Elsevier Masson, 2013, 341 (6), pp.547-552. Plus de détails...
High-resolution direct numerical simulations have shown the occurrence of inertia gravity waves simultaneously with baroclinic instabilities within a differentially heated rotating annulus, the "baroclinic cavity". The working fluid is characterised by a Prandtl number Pr = 16. A decomposition technique applied to the dependent variables has allowed us to separate in space and in time the contributions of the large-scale baroclinic structures from that of the small-scale fluctuations. These latter have been identified as inertia gravity waves from their dispersion relation. The present work is particularly focused on the mechanism responsible for the spontaneous generation of these waves.
Anthony Randriamampianina. Inertia gravity waves characteristics within a baroclinic cavity. Comptes Rendus Mécanique, Elsevier Masson, 2013, 341 (6), pp.547-552. <10.1016/j.crme.2013.01.006>. <hal-00946827>
Abdou Garba, Pierre Haldenwang. A Helmholtz--Hodge projection method using an iterative gauge computation to solve the 3D generalized Stokes problem. SIAM Journal on Scientific Computing, Society for Industrial and Applied Mathematics, 2013, 35 (3), pp.A1560-A1583. Plus de détails...
The generalized Stokes problem (GSP) is broadly recognized as a keystone in implicit or semi-implicit discretizations of the Navier--Stokes equations (NSE), either incompressible or of low Mach number type, i.e., for which there exists a constraint on the vector field. The GSP is also known as the steady Darcy--Brinkman model for flows in porous media or in Hele--Shaw configurations. Up to now, only pressure- (preconditioned) Uzawa methods claimed to solve the three-dimensional (3D) GSP exactly (i.e., without introducing an error due to some time stepping). In the present article, we present another exact 3D solver that is developed in the particular context of the Helmholtz--Hodge projection in $(H^1)^d$. Instead of working iteratively with the pressure operator (i.e., the Schur complement), we are interested here in using an alternative scalar field, which performs the projection and is called the gauge. It turns out that iterative computation of the gauge presents efficient properties in terms of operator conditioning. To prove the relevance of the gauge method, we demonstrate several mathematical properties of the operator acting on the gauge, especially when preconditioned in an appropriate way. In particular, we prove that the gauge operator can be solved efficiently with any gradient method. The convergence properties of the continuous preconditioned operator are quantitatively estimated in the context of a semiperiodic two-dimensional (2D) domain. We then study the discrete gauge operator implemented in the framework of Chebyshev 2D-3D pseudospectral methods. It exhibits the same favorable properties as those found for the continuous operator. Finally, we perform numerical experiments that corroborate our analyses.
Abdou Garba, Pierre Haldenwang. A Helmholtz--Hodge projection method using an iterative gauge computation to solve the 3D generalized Stokes problem. SIAM Journal on Scientific Computing, Society for Industrial and Applied Mathematics, 2013, 35 (3), pp.A1560-A1583. <10.1137/110860902>. <hal-00905812>
Guillaume Chiavassa, Bruno Lombard. Wave propagation across acoustic / Biot's media: a finite-difference method. Communications in Computational Physics, Global Science Press, 2013, 13 (4), pp.985-1012. Plus de détails...
Numerical methods are developed to simulate the wave propagation in heterogeneous 2D fluid / poroelastic media. Wave propagation is described by the usual acoustics equations (in the fluid medium) and by the low-frequency Biot's equations (in the porous medium). Interface conditions are introduced to model various hydraulic contacts between the two media: open pores, sealed pores, and imperfect pores. Well-possedness of the initial-boundary value problem is proven. Cartesian grid numerical methods previously developed in porous heterogeneous media are adapted to the present context: a fourth-order ADER scheme with Strang splitting for time-marching; a space-time mesh-refinement to capture the slow compressional wave predicted by Biot's theory; and an immersed interface method to discretize the interface conditions and to introduce a subcell resolution. Numerical experiments and comparisons with exact solutions are proposed for the three types of interface conditions, demonstrating the accuracy of the approach.
Guillaume Chiavassa, Bruno Lombard. Wave propagation across acoustic / Biot's media: a finite-difference method. Communications in Computational Physics, Global Science Press, 2013, 13 (4), pp.985-1012. <10.4208/cicp.140911.050412a>. <hal-00623627v2>
Dominique Morvan, Sofiane Meradji, William Mell. Interaction between head fire and backfire in grasslands. Fire Safety Journal, Elsevier, 2013, 58, pp.195-203. Plus de détails...
This paper deals with 3D numerical simulations of two fires fronts (head and backfire) propagating simultaneously through a grassland fuel. The simulations were carried out using a "fully" physical and three-dimensional fire model (namely WFDS). One of the objectives of this work, was to evaluate the potential for fully physical fire model to simulate the interactions between two fire fronts (a head fire and a backfire), in conditions similar to those encountered during suppression fire operations. A set of numerical simulations was first carried out for standalone head fires propagating through grasslands on a flat terrain and for various wind conditions ranging between 1 and 10 m/s. These results were compared with experimental data and numerical results from the literature. The same calculations were then repeated, with a backfire ignited at the downwind side of the plot. The numerical results highlighted that, for these particular conditions, head fire and backfire can interact, mainly, via two mechanisms: - at relatively large distances (greater than 10 m) the head fire acts on backfire as a screen and reduces the direct action of the wind flow on the backfire, - at relative small distances (nearly equal to 10 m) the gas flow (entrainment) generated in the vicinity of the head fire promotes the aspiration of the backfire towards the main fire front.
Dominique Morvan, Sofiane Meradji, William Mell. Interaction between head fire and backfire in grasslands. Fire Safety Journal, Elsevier, 2013, 58, pp.195-203. <10.1016/j.firesaf.2013.01.027>. <hal-01030810>
Journal: Fire Safety Journal
Date de publication: 01-01-2013
Auteurs:
Dominique Morvan
Sofiane Meradji
William Mell
2012
A. Lamorlette, A. Collin. Analytical quantification of convective heat transfer inside vegetal structures. International Journal of Thermal Sciences, Elsevier, 2012, 57, pp.78-84. Plus de détails...
Within the scope of environmental modelling, convective heat transfer between a vegetal structure and its surrounding medium remains to be adequately described. However, for some applications, such as forest fire modelling, convective heat transfer is one of the factors responsible for vertical fire transitions, from ground level to the tree crowns. These fires are the most dangerous because their rates of spread can reach high speeds, around 1 m per second. An accurate characterization of this transfer is therefore important for fire propagation modelling. This study presents an attempt to formulate an analytical modelling of the convective heat transfer coefficient inside vegetal structures generated using an Iterated Function Systems (IFS) which only depends on the IFS parameters (parameters helpful to generate vegetal structures). The results obtained using this formula are compared with previously computed numerical results to evaluate their accuracy. The maximal discrepancies were found to be around 6% which proves the efficiency of the present model.
A. Lamorlette, A. Collin. Analytical quantification of convective heat transfer inside vegetal structures. International Journal of Thermal Sciences, Elsevier, 2012, 57, pp.78-84. <10.1016/j.ijthermalsci.2012.02.010>. <hal-01297730>
Journal: International Journal of Thermal Sciences
G.H. Lopes, B. Bernales Chavez, Nelson Ibaseta, Pierrette Guichardon, Pierre Haldenwang. Prediction of Permeate Flux and Rejection Rate in RO and NF Membrane Processes: Numerical Modelling of Hydrodynamics and Mass Transfer Coupling. Procedia Engineering, Elsevier, 2012, 44, pp.1934-1936. Plus de détails...
G.H. Lopes, B. Bernales Chavez, Nelson Ibaseta, Pierrette Guichardon, Pierre Haldenwang. Prediction of Permeate Flux and Rejection Rate in RO and NF Membrane Processes: Numerical Modelling of Hydrodynamics and Mass Transfer Coupling. Procedia Engineering, Elsevier, 2012, 44, pp.1934-1936. <10.1016/j.proeng.2012.09.001>. <hal-01299944>
A. Lamorlette, A. Collin, O. Sro-Guillaume. Characterization of heat transfer between phases inside a porous medium as applied to vegetal set representations. International Journal of Heat and Mass Transfer, Elsevier, 2012, 55 (4), pp.607-617. Plus de détails...
Convective heat transfer between vegetal sets and the surrounding air in the context of forest fires has not yet been fully investigated and understood in existing studies. This process may have a great influence on many environmental problems such as forest fires. This study is devoted to the computational heat transfer characterization of tree structures. These structures were generated by Iterated Function Systems (IFS) and the fluid flow was computed using balance equations (mass, momentum, heat, etc.). The heat transfer was then characterized using the macroscopic Stanton number on several tree structures. The main objective of this study was to demonstrate that the macroscopic Stanton number only depends on the macroscopic Reynolds number using a power law. In addition, the power law exponent was found to be quasi-constant for all the configurations tested in this work and it tends to be universal.
A. Lamorlette, A. Collin, O. Sro-Guillaume. Characterization of heat transfer between phases inside a porous medium as applied to vegetal set representations. International Journal of Heat and Mass Transfer, Elsevier, 2012, 55 (4), pp.607-617. <10.1016/j.ijheatmasstransfer.2011.10.051>. <hal-01297728>
Journal: International Journal of Heat and Mass Transfer
Wave propagation in a stratified fluid / porous medium is studied here using analytical and numerical methods. The semi-analytical method is based on an exact stiffness matrix method coupled with a matrix conditioning procedure, preventing the occurrence of poorly conditioned numerical systems. Special attention is paid to calculating the Fourier integrals. The numerical method is based on a high order finite-difference time-domain scheme. Mesh refinement is applied near the interfaces to discretize the slow compressional diffusive wave predicted by Biot's theory. Lastly, an immersed interface method is used to discretize the boundary conditions. The numerical benchmarks are based on realistic soil parameters and on various degrees of hydraulic contact at the fluid / porous boundary. The time evolution of the acoustic pressure and the porous velocity is plotted in the case of one and four interfaces. The excellent level of agreement found to exist between the two approaches confirms the validity of both methods, which cross-checks them and provides useful tools for future researches.
Gaëlle Lefeuve-Mesgouez, Arnaud Mesgouez, Guillaume Chiavassa, Bruno Lombard. Semi-analytical and numerical methods for computing transient waves in 2D acoustic / poroelastic stratified media. Wave Motion, Elsevier, 2012, 49-7, pp.667-680. <10.1016/j.wavemoti.2012.04.006>. <hal-00667795v2>
Aymeric Lamorlette, Anthony Collin. Analytical quantification of convective heat transfer inside vegetal structures. International Journal of Thermal Sciences, Elsevier, 2012, 57, pp.78-84. Plus de détails...
Within the scope of environmental modelling, convective heat transfer between a vegetal structure and its surrounding medium remains to be adequately described. However, for some applications, such as forest fire modelling, convective heat transfer is one of the factors responsible for vertical fire transitions, from ground level to the tree crowns. These fires are the most dangerous because their rates of spread can reach high speeds, around 1 m per second. An accurate characterization of this transfer is therefore important for fire propagation modelling. This study presents an attempt to formulate an analytical modelling of the convective heat transfer coefficient inside vegetal structures generated using an Iterated Function Systems (IFS) which only depends on the IFS parameters (parameters helpful to generate vegetal structures). The results obtained using this formula are compared with previously computed numerical results to evaluate their accuracy. The maximal discrepancies were found to be around 6% which proves the efficiency of the present model.
Aymeric Lamorlette, Anthony Collin. Analytical quantification of convective heat transfer inside vegetal structures. International Journal of Thermal Sciences, Elsevier, 2012, 57, pp.78-84. <10.1016/j.ijthermalsci.2012.02.010>. <hal-01297730>
Journal: International Journal of Thermal Sciences
Experiments were carried out on reversed weak laminar inclined fountains to asses that unstable modes of round fountains are disturbed by the inclination. Indeed, compared to fountains developing on horizontal wall, some modes disappeared while others are split in several modes. This paper aims at describing and mapping these new modes regarding to the inclination and the inlet velocity. Explanations about what made the unstable modes evolve are also proposed. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Evelyne Neau, Joan Escandell, Isabelle Raspo. A generalized reference state at constant volume for the prediction of phase equilibria from low pressure model parameters: application to size-asymmetric systems and to the Wong-Sandler mixing rule. Chemical Engineering Science, Elsevier, 2011, 66 (18), pp.4148-4156. Plus de détails...
This paper describes an EoS/GE approach based on cubic equations of state making reference to low pressure GE models derived from the lattice fluid theory of Guggenheim. The proposed method does not present the theoretical problems encountered with the literature reference states (infinite pressure of Huron-Vidal, zero pressure of Michelsen and constant packing fraction of Péneloux), namely the description of the alpha function with combinatorial terms derived from both the excess Gibbs energy model and the EoS. The main advantage of the proposed method is to successfully account for the size-asymmetry of mixture components and to improve the results obtained with the Wong-Sandler mixing rule. Comparisons are performed with the MHV1, LCVM and the original Wong-Sandler approach at infinite pressure.
Evelyne Neau, Joan Escandell, Isabelle Raspo. A generalized reference state at constant volume for the prediction of phase equilibria from low pressure model parameters: application to size-asymmetric systems and to the Wong-Sandler mixing rule. Chemical Engineering Science, Elsevier, 2011, 66 (18), pp.4148-4156. <10.1016/j.ces.2011.05.043>. <hal-01023163>
Guillaume Chiavassa, Bruno Lombard. Time domain numerical modeling of wave propagation in 2D heterogeneous porous media. Journal of Computational Physics, Elsevier, 2011, 230 (13), pp.5288-5309. Plus de détails...
This paper deals with the numerical modeling of wave propagation in porous media described by Biot's theory. The viscous efforts between the fluid and the elastic skeleton are assumed to be a linear function of the relative velocity, which is valid in the low-frequency range. The coexistence of propagating fast compressional wave and shear wave, and of a diffusive slow compressional wave, makes numerical modeling tricky. To avoid restrictions on the time step, the Biot's system is splitted into two parts: the propagative part is discretized by a fourth-order ADER scheme, while the diffusive part is solved analytically. Near the material interfaces, a space-time mesh refinement is implemented to capture the small spatial scales related to the slow compressional wave. The jump conditions along the interfaces are discretized by an immersed interface method. Numerical experiments and comparisons with exact solutions confirm the accuracy of the numerical modeling. The efficiency of the approach is illustrated by simulations of multiple scattering.
Guillaume Chiavassa, Bruno Lombard. Time domain numerical modeling of wave propagation in 2D heterogeneous porous media. Journal of Computational Physics, Elsevier, 2011, 230 (13), pp.5288-5309. <10.1016/j.jcp.2011.03.030>. <hal-00547008v2>
K. Gavrilov, Dominique Morvan, Gilbert Accary, D.V. Lyubimov, Sofiane Meradji, et al.. Numerical modeling of coherent structures attendant on impurity propagation in the atmospheric boundary layer over a forest canopy. Fluid Dynamics / Izvestiya Akademii Nauk - Mekhanika Zhidkosti i Gaza, MAIK Nauka/Interperiodica (МАИК Наука/Интерпериодика), 2011, 46 (1), pp.138-147. Plus de détails...
Three-dimensional large eddy simulation is used to solve the problem for a homogeneous forest canopy. The development of the Kelvin-Helmholtz instability above the canopy leads to the formation of coherent structures in the atmosphere flow, which are reproduced in the calculations. The statistical characteristics of the flow obtained from the numerical modeling are compared with experimental data. The passive admixture transfer from the canopy to the clean atmosphere is studied for two cases, namely, for constant and variable coupled concentration of the impurity in the canopy.
K. Gavrilov, Dominique Morvan, Gilbert Accary, D.V. Lyubimov, Sofiane Meradji, et al.. Numerical modeling of coherent structures attendant on impurity propagation in the atmospheric boundary layer over a forest canopy. Fluid Dynamics / Izvestiya Akademii Nauk - Mekhanika Zhidkosti i Gaza, MAIK Nauka/Interperiodica (МАИК Наука/Интерпериодика), 2011, 46 (1), pp.138-147. <10.1134/S0015462811010169>. <hal-01030826>
Journal: Fluid Dynamics / Izvestiya Akademii Nauk - Mekhanika Zhidkosti i Gaza
Date de publication: 01-01-2011
Auteurs:
K. Gavrilov
Dominique Morvan
Gilbert Accary
D.V. Lyubimov
Sofiane Meradji
Oleg A. Bessonov
2011
Jérôme Julien, Mihail Garajeu, Jean-Claude Michel. A semi-analytical model for the behavior of saturated viscoplastic materials containing two populations of voids of different sizes. International Journal of Solids and Structures, Elsevier, 2011, 48 (10), pp.1485-1498. Plus de détails...
This paper presents a micromechanical model for a porous viscoplastic material containing two populations of pressurized voids of different sizes. Three scales are distinguished: the microscopic scale (corresponding to the size of the small voids), the mesoscopic scale (corresponding to the size of the large voids) and the macroscopic scale. It is assumed that the first homogenization step is performed at the microscopic scale, and, at the mesoscopic scale, the matrix is taken to be homogeneous and compressible. At the mesoscopic scale, the second homogenization step, on which the present study focuses, is based on a simplified representative volume element: a hollow sphere containing a pressurized void surrounded by a nonlinear viscoplastic compressible matrix. The nonlinear behavior of the matrix, which is expressed using the results obtained in the first homogenization step, is approached using a modified secant linearization procedure involving the discretization of the hollow sphere into concentric layers. Each layer has uniform secant moduli. The predictions of the model are compared with the more accurate numerical results obtained using the finite element method. Good agreement is found to exist with all the macroscopic stress triaxialities and all the porosity and nonlinearity values studied.
Jérôme Julien, Mihail Garajeu, Jean-Claude Michel. A semi-analytical model for the behavior of saturated viscoplastic materials containing two populations of voids of different sizes. International Journal of Solids and Structures, Elsevier, 2011, 48 (10), pp.1485-1498. <10.1016/j.ijsolstr.2011.01.031>. <hal-00583378>
Journal: International Journal of Solids and Structures
Dominique Morvan, Chad Hoffman, Francisco Rega, William Mell. Numerical simulation of the interaction between two fire fronts in grassland and shrubland. Fire Safety Journal, Elsevier, 2011, 46 (8), pp.469-479. Plus de détails...
The objective of this paper was to evaluate the potential for fully physical fire models to simulate the interactions between two converging fire fronts (a head fire and a back fire), in conditions similar to those encountered during suppression fire operations. The simulations were carried out using two fully physical models: FIRESTAR, in two dimensions, and Wildland Fire Dynamics Simulator, in three dimensions. Each modelling approach numerically solves a set of balance equations (mass, momentum, energy, etc.) governing the behaviour of the coupled system formed by the vegetation and the surrounding atmosphere. Two fuel profiles were tested: homogeneous grassland similar to landscapes in Australia and a shrubland representative of Mediterranean landscape (garrigue). Results from the two-dimensional and three-dimensional simulations were used to investigate how the two fire fronts interact together and mutually modify, or not, their own behaviour before merging. The results of these simulations showed that the merging of two fire fronts can result in a quick increase in fire-line intensity or in flame height. We concluded that physics-based simulations do reproduce reasonable and expected head- and back-fire interactions, but more work is needed to further understand the accuracy of such predictions.
Dominique Morvan, Chad Hoffman, Francisco Rega, William Mell. Numerical simulation of the interaction between two fire fronts in grassland and shrubland. Fire Safety Journal, Elsevier, 2011, 46 (8), pp.469-479. <10.1016/j.firesaf.2011.07.008>. <hal-01022562>
Journal: Fire Safety Journal
Date de publication: 01-01-2011
Auteurs:
Dominique Morvan
Chad Hoffman
Francisco Rega
William Mell
2011
Dominique Morvan. Physical phenomena and length scales governing the behaviour of wildfires: a case for physical modelling. Fire Technology, Springer Verlag, 2011, 47 (2), pp.437-460. Plus de détails...
This paper is an overview of the physical mechanisms and length scales governing the propagation of wildfires. One of the objectives is to identify the physical and mathematical constraints in the modelling of wildfires when using a "fully" physical approach. The literature highlights two regimes in the propagation of surface fires, i.e. wind-driven fires and plume-dominated fires, which are governed by radiation and convective heat transfer, respectively. This division leads to the identification of two governing length scales: the extinction length characterising the absorption of radiation by vegetation, and the integral turbulent length scale characterising the interaction between wind and canopy. Some numerical results published during the last decade using a fully physical approach are presented and discussed with a focus on the models FIRESTAR, FIRELES, FIRETEC and WFDS. Numerical simulations were compared with experimental data obtained at various scales, from laboratory to field fires in grassland and in Mediterranean shrubland. Some perspectives are presented concerning the potential coupling between physical fire models with mesoscale atmospheric models to study the impacts of wildfires at larger scale. Some of the topics on wildfire physical modelling that need further research are identified in the conclusions.
Dominique Morvan. Physical phenomena and length scales governing the behaviour of wildfires: a case for physical modelling. Fire Technology, Springer Verlag, 2011, 47 (2), pp.437-460. <10.1007/s10694-010-0160-2>. <hal-01022589>
Journal: Fire Technology
Date de publication: 01-01-2011
Auteurs:
Dominique Morvan
2011
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S574-S578. Plus de détails...
We are interested here in modelling the electron and ion temperature fields, Te and Ti respectively, in order to understand the main trends that govern the ratio Ti/Te that is being better documented in the SOL with RFA probes and . The experimental evidence gathered from several devices indicates that this temperature ratio significantly exceeds unity in most data sets that have been analysed, including measurements in the SOL of limiter devices like Tore Supra. Several issues of interest have been addressed with this version of the SOLEDGE-2D code. First, we have analysed the width of the SOL heat channels to the wall components and compared these values to analytical expressions. The key control mechanism of the width of the SOL heat channel is given by a balance between the sheath boundary conditions and the transverse transport. More advanced simulations address the interplay between the edge and SOL plasma allowing one to recover regimes with Ti/Te > 1.
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, Elsevier, 2011, 415 (1), pp.S574-S578. <10.1016/j.jnucmat.2010.12.318>. <hal-00848528>
Konstantin Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Sofiane Meradji, et al.. Numerical simulation of coherent structures over plant canopy. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2011, 86 (1), pp.89-111. Plus de détails...
This paper reports large eddy simulations of the interaction between an atmospheric boundary layer and a canopy (representing a forest cover). The problem is studied for a homogeneous configuration representing the situation encountered above a continuous forest cover, as well as for a heterogeneous configuration representing the situation similar to an edge or a clearing in a forest. The numerical results reproduces correctly all the main characteristics of this flow as reported in the literature: the formation of a first generation of coherent structures aligned transversally with the wind flow direction, the reorganization and the deformation of these vortex tubes into horse-shoe structures. The results obtained when introducing a discontinuity in the canopy (reproducing a clearing or a fuel break in a forest), are compared with the experimental data collected in a wind tunnel; here, the results confirm the existence of a strong turbulence activity inside the canopy at a distance equal to 8 times the height of the canopy, referenced in the literature as the Enhance Gust Zone (EGZ) characterized by a local peak of the skewness factor.
Konstantin Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Sofiane Meradji, et al.. Numerical simulation of coherent structures over plant canopy. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2011, 86 (1), pp.89-111. <10.1007/s10494-010-9294-z>. <hal-01022574>
Journal: Flow, Turbulence and Combustion
Date de publication: 01-01-2011
Auteurs:
Konstantin Gavrilov
Gilbert Accary
Dominique Morvan
Dimitry Lyubimov
Sofiane Meradji
Oleg A. Bessonov
2010
Sébastien Poncet, Sofia Haddadi, Stéphane Viazzo. Numerical modeling of fluid flow and heat transfer in a narrow Taylor-Couette-Poiseuille system. International Journal of Heat and Fluid Flow, Elsevier, 2010, 32, pp.128-144. Plus de détails...
We consider turbulent flows in a differentially heated Taylor-Couette system with an axial Poiseuille flow. The numerical approach is based on the Reynolds Stress Modeling (RSM) of Elena and Schiestel widely validated in various rotor-stator cavities with throughflow. To show the capability of the present code, our numerical predictions are compared very favorably to the velocity measurements of Escudier and Gouldson in the isothermal case, for both the mean and turbulent fields. The RSM model improves, in particular, the predictions of the k-eps model of Naser. Then, the second order model is applied for a large range of rotational Reynolds and Prandtl numbers, flow rate coefficient in a very narrow cavity of radius ratio s=0.961 and aspect ratio L=0.013. Temperature gradients are imposed between the incoming fluid and the inner and outer cylinders. The mean hydrodynamic and thermal fields reveal three distinct regions across the radial gap with a central region of almost constant axial and tangential mean velocities and constant mean temperature. Turbulence, which is weakly anisotropic, is mainly concentrated in that region and vanishes towards the cylinders. The mean velocity distributions are not clearly affected by the rotational Reynolds number and the flow rate coefficient. The effects of the flow parameters on the thermal field are more noticeable and considered in details. Correlations for the averaged Nusselt numbers along both cylinders are finally provided according to the flow control parameters.
Sébastien Poncet, Sofia Haddadi, Stéphane Viazzo. Numerical modeling of fluid flow and heat transfer in a narrow Taylor-Couette-Poiseuille system. International Journal of Heat and Fluid Flow, Elsevier, 2010, 32, pp.128-144. <10.1016/j.ijheatfluidflow.2010.08.003>. <hal-00678877>
Journal: International Journal of Heat and Fluid Flow
Colette Nicoli, Pierre Haldenwang. A resonant response of self-pulsating spray-flame submitted to acoustic wave. Combustion Science and Technology, Taylor & Francis, 2010, 182 (4-6), pp.559-573. Plus de détails...
Recently, experiments and theoretical investigations have shown that spray flame can exhibit oscillatory regimes for standard set of parameters. Theoretical and numerical investigations on flame propagation in two-phase premixtures have put forward an intrinsic (and robust) mechanism based on the interaction between the locus where droplets vaporize and the reaction zone. This mechanism invokes neither droplet inertia (very small droplets are studied) nor differential diffusive effects (pulsations take place for unity Lewis number, too). Self-oscillations of spray-flame occur as in a supercritical Hopf bifurcation, controlled by Zeldovich number (Ze, the reduced activation energy), the onset threshold being on the order of (Ze)c ≈ 10. The issue addressed in this contribution is whether acoustic wave and self-pulsating spray-flame can interact. This study was carried out in the open-loop context: a spray-flame was submitted to small amplitude fluctuations of pressure; the gain toward acoustics was found as depending on Zeldovich number because energy transfer is found magnified in the case of a close-frequency fit between acoustic resonator and natural spray-flame oscillations. Moreover, energy transfer is found as of resonant type.
Colette Nicoli, Pierre Haldenwang. A resonant response of self-pulsating spray-flame submitted to acoustic wave. Combustion Science and Technology, Taylor & Francis, 2010, 182 (4-6), pp.559-573. <10.1080/00102200903465915>. <hal-00907320>
Дмитрий Викторович Любимов, Константин Алексеевич Гаврилов, Dominique Morvan, Gilbert Accary, Sofiane Meradji, et al.. Численное моделирование когерентных структур при распростра-нении примеси в атмосферном пограничном слое над лесным пологом. Вычислительная механика сплошных сред, 2010, 3 (2), pp.34--45. Plus de détails...
Дмитрий Викторович Любимов, Константин Алексеевич Гаврилов, Dominique Morvan, Gilbert Accary, Sofiane Meradji, et al.. Численное моделирование когерентных структур при распростра-нении примеси в атмосферном пограничном слое над лесным пологом. Вычислительная механика сплошных сред, 2010, 3 (2), pp.34--45. <hal-01291552>
Journal: Вычислительная механика сплошных сред
Date de publication: 01-01-2010
Auteurs:
Дмитрий Викторович Любимов
Константин Алексеевич Гаврилов
Dominique Morvan
Gilbert Accary
Sofiane Meradji
Олег Аркадьевич Бессонов
2010
K. Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Oleg A. Bessonov, et al.. Large eddy simulation of coherent structures over forest canopy. Deville M., Lê T-H., Sagaut P. Turbulence and Interactions: proceedings the TI 2009 conference, Springer Berlin Heidelberg, pp.143-149, 2010, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 978-3-642-14138-6. Plus de détails...
This paper deals with the numerical simulation (using a LES approach) of the interaction between an atmospheric boundary layer (ABL) and a canopy, representing a forest cover. This problem was studied for a homogeneous configuration representing the situation encountered above a continuous forest cover, and a heterogeneous configuration representing the situation similar to an edge or a clearing in a forest. The numerical results, reproduced correctly all the main characteristics of this flow, as reported in the literature: the formation of a first generation of coherent structures aligned transversally from the wind flow direction, the reorganisation and the deformation of these vortex tubes to horse shoe structures. The results obtained, introducing a discontinuity in the canopy (reproducing a clearing or a fuel break in a forest), were compared with experimental data collected in a wind tunnel. The results confirmed the existence of a strong turbulence activity inside the canopy at a distance equal to 8 times the height of the canopy, referenced in the literature as an Enhance Gust Zone (EGZ) characterized by a local peak of the skewness factor.
K. Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Oleg A. Bessonov, et al.. Large eddy simulation of coherent structures over forest canopy. Deville M., Lê T-H., Sagaut P. Turbulence and Interactions: proceedings the TI 2009 conference, Springer Berlin Heidelberg, pp.143-149, 2010, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 978-3-642-14138-6. <10.1007/978-3-642-14139-3_17>. <hal-01024672>
Date de publication: 01-01-2010
Auteurs:
K. Gavrilov
Gilbert Accary
Dominique Morvan
Dimitry Lyubimov
Oleg A. Bessonov
Sofiane Meradji
2010
Mounir Alliche, Pierre Haldenwang, Salah Chikh. Extinction conditions of a premixed flame in a channel. Combustion and Flame, Elsevier, 2010, 157 (6), pp.1060-1070. Plus de détails...
A local refinement method is used to numerically predict the propagation and extinction conditions of a premixed flame in a channel considering a thermodiffusive model. A local refinement method is employed because of the numerous length scales that characterize this phenomenon. The time integration is self adaptive and the solution is based on a multigrid method using a zonal mesh refinement in the flame reaction zone. The objective is to determine the conditions of extinction which are characterized by the flame structure and its properties. We are interested in the following properties: the curvature of the flame, its maximum temperature, its speed of propagation and the distance separating the flame from the wall. We analyze the influence of heat losses at the wall through the thermal conductivity of the wall and the nature of the fuel characterized by the Lewis number of the mixture. This investigation allows us to identify three propagation regimes according to heat losses at the wall and to the channel radius. The results show that there is an intermediate value of the radius for which the flame can bend and propagate provided that its curvature does not exceed a certain limit value. Indeed, small values of the radius will choke the flame and extinguish it. The extinction occurs if the flame curvature becomes too small. Furthermore, this study allows us to predict the limiting values of the heat loss coefficient at extinction as well as the critical value of the channel radius above which the premixed flame may propagate without extinction. A dead zone of length 2-4 times the flame thickness appears between the flame and the wall for a Lewis number (Le) between 0.8 and 2. For small values of Le, local extinctions are observed.
Mounir Alliche, Pierre Haldenwang, Salah Chikh. Extinction conditions of a premixed flame in a channel. Combustion and Flame, Elsevier, 2010, 157 (6), pp.1060-1070. <10.1016/j.combustflame.2010.02.006>. <hal-00907298>
Guillaume Chiavassa, Bruno Lombard, Joël Piraux. Numerical modeling of 1-D transient poroelastic waves in the low-frequency range. Journal of Computational and Applied Mathematics, Elsevier, 2010, 234, pp.1757-1765. Plus de détails...
Propagation of transient mechanical waves in porous media is numerically investigated in 1D. The framework is the linear Biot's model with frequency-independant coefficients. The coexistence of a propagating fast wave and a diffusive slow wave makes numerical modeling tricky. A method combining three numerical tools is proposed: a fourth-order ADER scheme with time-splitting to deal with the time-marching, a space-time mesh refinement to account for the small-scale evolution of the slow wave, and an interface method to enforce the jump conditions at interfaces. Comparisons with analytical solutions confirm the validity of this approach.
Guillaume Chiavassa, Bruno Lombard, Joël Piraux. Numerical modeling of 1-D transient poroelastic waves in the low-frequency range. Journal of Computational and Applied Mathematics, Elsevier, 2010, 234, pp.1757-1765. <10.1016/j.cam.2009.08.025>. <hal-00193103v2>
Journal: Journal of Computational and Applied Mathematics
Olivier Boiron, Guillaume Chiavassa, Rosa Donat. A High-Resolution Penalization Method for large Mach number Flows in the presence of Obstacles. Computers and Fluids, Elsevier, 2009, 38 (3), pp.703-714. Plus de détails...
A penalization method is applied to model the interaction of large Mach number compressible flows with obstacles. A supplementary term is added to the compressible Navier-Stokes system, seeking to simulate the effect of the Brinkman-penalization technique used in incompressible flow simulations including obstacles. We present a computational study comparing numerical results obtained with this method to theoretical results and to simulations with Fluent software. Our work indicates that this technique can be very promising in applications to complex flows.
Olivier Boiron, Guillaume Chiavassa, Rosa Donat. A High-Resolution Penalization Method for large Mach number Flows in the presence of Obstacles. Computers and Fluids, Elsevier, 2009, 38 (3), pp.703-714. <10.1016/j.compfluid.2008.07.003>. <hal-00259907v2>
D Morvan, Sofiane Meradji, G Accary. Physical modelling of fire spread in grasslands. Fire Safety Journal, Elsevier, 2009, 44 (1), pp.50--61. Plus de détails...
D Morvan, Sofiane Meradji, G Accary. Physical modelling of fire spread in grasslands. Fire Safety Journal, Elsevier, 2009, 44 (1), pp.50--61. <hal-01291553>
Gilbert Accary, Sofiane Meradji, Dominique Fougere, Dominique Morvan. Towards a numerical benchmark for 3D mixed-convection low Mach number flows in a rectangular channel heated from below. Journal of Fluid Dynamics and Material Science, 2008, 141 (1), p. 1-7. Plus de détails...
Gilbert Accary, Sofiane Meradji, Dominique Fougere, Dominique Morvan. Towards a numerical benchmark for 3D mixed-convection low Mach number flows in a rectangular channel heated from below. Journal of Fluid Dynamics and Material Science, 2008, 141 (1), p. 1-7. <hal-00271502>
Journal: Journal of Fluid Dynamics and Material Science
Sébastien Poncet, Anthony Randriamampianina. Three-dimensional turbulent boundary layer in a shrouded rotating system. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2008, 80 (1), pp.107-117. Plus de détails...
A three-dimensional direct numerical simulation is combined with a laboratory study to describe the turbulent flow in an enclosed annular rotor-stator cavity characterized by a large aspect ratio G=(b-a)/h=18.32 and a small radius ratio a/b=0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate $\Omega$ considered is equivalent to the rotational Reynolds number $Re=\Omega b^2/\nu=9.5 \times 10^4$ ($\nu$ the kinematic viscosity of water). This corresponds to a value at which experiment has revealed that the stator boundary layer is turbulent, whereas the rotor boundary layer is still laminar. Comparisons of the computed solution with velocity measurements have given good agreement for the mean and turbulent fields. The results enhance evidence of weak turbulence by comparing the turbulence properties with available data in the literature (Lygren & Andersson, J Fluid Mech 426:297-326, 2001). An approximately self-similar boundary layer behavior is observed along the stator. The wall-normal variations of the structural parameter and of characteristic angles confirm that this boundary layer is three-dimensional. A quadrant analysis (Kang et al, Phys Fluids 10:2315-2322, 1998) of conditionally averaged velocities shows that the asymmetries obtained are dominated by Reynolds stress-producing events in the stator boundary layer. Moreover, Case 1 vortices (with a positive wall induced velocity) are found to be the major source of generation of special strong events, in agreement with the conclusions of Lygren and Andersson (J Fluid Mech 426:297-326, 2001).
Sébastien Poncet, Anthony Randriamampianina. Three-dimensional turbulent boundary layer in a shrouded rotating system. Flow, Turbulence and Combustion, Springer Verlag (Germany), 2008, 80 (1), pp.107-117. <10.1007/s10494-007-9083-5>. <hal-00192950>
Mihail Garajeu, Pierre Suquet. On the influence of local fluctuations in volume fraction of constituents on the effective properties of nonlinear composites. Application to porous materials. Journal of the Mechanics and Physics of Solids, Elsevier, 2007, 55 (4), pp.842-878. Plus de détails...
Composite materials often exhibit local fluctuations in the volume fraction of their individual constituents. This paper studies the influence of such small fluctuations on the effective properties of composites. A general asymptotic expansion of these properties in terms of powers of the amplitude of the fluctuations is given first. Then, this general result is applied to porous materials. As is well-known, the effective yield surface of ductile voided materials is accurately described by Gurson's criterion. Suitable extensions for viscoplastic solids have also been proposed. The question addressed in the present study pertains to nonuniform distributions of voids in a typical volume element or in other words to the presence of matrix-rich and pore-rich zones in the material. It is shown numerically and analytically that such deviations from a uniform distribution result in a weakening of the macroscopic carrying capacity of the material.
Mihail Garajeu, Pierre Suquet. On the influence of local fluctuations in volume fraction of constituents on the effective properties of nonlinear composites. Application to porous materials. Journal of the Mechanics and Physics of Solids, Elsevier, 2007, 55 (4), pp.842-878. <10.1016/j.jmps.2006.09.005>. <hal-00214721>
Journal: Journal of the Mechanics and Physics of Solids
Pierre Haldenwang. Laminar flow in a two-dimensional plane channel with local pressure-dependent crossflow. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2007, 593, pp.463-473. Plus de détails...
Long ducts (or pipes) composed of transpiring (e.g. porous) walls are at the root of numerous industrial devices for species separation, as tangential filtration or membrane desalination. Similar configurations can also be involved in fluid supply systems, as irrigation or biological fluids in capillaries. A transverse leakage (or permeate flux), the strength of which is assumed to depend linearly on local pressure (as in Starling's law for capillary), takes place through permeable walls. All other dependences, as osmotic pressure or partial fouling due to polarization of species concentration, are neglected. To analyse this open problem we consider the simplest situation: the steady laminar flow in a two-dimensional channel composed of two symmetrical porous walls. First, dimensional analysis helps us to determine the relevant parameters. We then revisit the Berman problem that considers a uniform crossflow (i.e. pressure-independent leakage). We expand the solution in a series of Rt, the transverse Reynolds number. We note this series has a rapid convergence in the considered range of Rt (i.e. Rt ≤ O(1)). A particular method of variable separation then allows us to derive from the Navier-Stokes equations two new ordinary differential equations (ODE), which correspond to first and second orders in the development in Rt, whereas the zero order recovers the Regirer linear theory. Finally, both new ODEs are used to study the occurrence of two undesirable events in the filtration process: axial flow exhaustion (AFE) and crossflow reversal (CFR). This study is compared with a numerical approach.
Pierre Haldenwang. Laminar flow in a two-dimensional plane channel with local pressure-dependent crossflow. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2007, 593, pp.463-473. <10.1017/S0022112007008622>. <hal-00907372>
Isabelle Raspo, Sofiane Meradji, Bernard Zappoli. Heterogeneous reaction induced by the piston effect in supercritical binary mixtures. Chemical Engineering Science, Elsevier, 2007, 62 (16), pp.4182-4192. Plus de détails...
It is now well established that the large compressibility of supercritical fluids is responsible for the strong enhancement of the thermo-acoustic heating, leading to the speeding up of the heat transport thanks to the piston effect instead of the expected slowing down. We show in this paper, through numerical simulations, that the hydrodynamics behavior of supercritical fluids also couples with the critical behavior of the solubility of solids to cause the release of a heterogeneous reaction at solid surfaces in dilute binary supercritical mixtures.
Isabelle Raspo, Sofiane Meradji, Bernard Zappoli. Heterogeneous reaction induced by the piston effect in supercritical binary mixtures. Chemical Engineering Science, Elsevier, 2007, 62 (16), pp.4182-4192. <10.1016/j.ces.2007.04.027>. <hal-01139223>
D Morvan, Sofiane Meradji, G Accary. Wildfire behavior study in a Mediterranean pine stand using a physically based model. Combustion Science and Technology, Taylor & Francis, 2007, 180 (2), pp.230--248. Plus de détails...
D Morvan, Sofiane Meradji, G Accary. Wildfire behavior study in a Mediterranean pine stand using a physically based model. Combustion Science and Technology, Taylor & Francis, 2007, 180 (2), pp.230--248. <hal-01291554>
Colette Nicoli, Pierre Haldenwang, S. Suard. Effects of substituting fuel spray for fuel gas on flame stability in lean premixtures. Combustion and Flame, Elsevier, 2007, 149 (3), pp.295-313. Plus de détails...
We analyze flame propagation through a homogeneous three-component premixture composed of fuel gas, small fuel droplets, and air. This analytical study is carried out within the framework of a diffusional-thermal model with the simplifying assumption that both fuels--the fuel in the gaseous phase and the gaseous fuel evaporating from the droplets--have the same Lewis number. The parameter that expresses the degree of substitution of spray for gas is δ, the liquid loading, i.e., the ratio of liquid fuel mass fraction to overall fuel mass fraction in the fresh premixture. In this substitution of liquid fuel for gaseous fuel, the overall equivalence ratio is lean and is kept identical. We hence obtain a partially prevaporized spray, for which we analytically study the dynamics of the plane spray-flame front. The investigated model assumes the averaged distance between droplets to be small compared with the premixed flame thickness (i.e., small droplets and moderate pressure). Le, the Lewis number, Ze, the Zeldovich number, and δ are the main parameters of the study. Our stability analysis supplies the stability diagram in the plane {Le,δ} for various Ze values and shows that, for all Le, the plane front becomes unstable for high liquid loading. At large or moderate Lewis number, we show that the presence of droplets substantially diminishes the onset threshold of the oscillatory instability, making the appearance of oscillatory propagation easier. Oscillations can even occur for Le<1 when sufficient spray substitution is operated. The pulsation frequency occurring in this regime is a tunable function of δ. At low Lewis number, substitution of spray for gas leads to a more complex situation for which two branches can coexist: the first one still corresponding to the pulsating regime, the other one being related to the diffusive-thermal cellular instability.
Colette Nicoli, Pierre Haldenwang, S. Suard. Effects of substituting fuel spray for fuel gas on flame stability in lean premixtures. Combustion and Flame, Elsevier, 2007, 149 (3), pp.295-313. <10.1016/j.combustflame.2006.12.018>. <hal-00907387>
M. Forestier, Pierre Haldenwang. Natural convection along a heated vertical plate immersed in a nonlinearly stratified medium: application to liquefied gas storage. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2007, 588, pp.217-241. Plus de détails...
We consider free convection driven by a heated vertical plate immersed in a nonlinearly stratified medium. The plate supplies a uniform horizontal heat flux to a fluid, the bulk of which has a stable stratification, characterized by a non-uniform vertical temperature gradient. This gradient is assumed to have a typical length scale of variation, denoted Z0, while Ψ0 is the order of magnitude of the related heat flux that crosses the medium vertically. We derive an analytic solution to the Boussinesq equations that extends the classical solution of Prandtl to the case of nonlinearly stratified media. This novel solution is asymptotically valid in the regime Ras " 1, where Ras denotes the Rayleigh number of nonlinear stratification, based on Z0, Ψ0, and the physical properties of the medium. We then apply the new theory to the natural convection affecting the vapour phase in a liquefied pure gas tank (e.g. the cryogenic storage of hydrogen). It is assumed that the cylindrical storage tank is subject to a constant uniform heat flux on its lateral and top walls. We are interested in the vapour motion above a residual layer of liquid in equilibrium with the vapour. High-precision axisymmetric numerical computations show that the flow remains steady for a large range of parameters, and that a bulk stratification characterized by a quadratic temperature profile is undoubtedly present. The application of the theory permits a comparison of the numerical and analytic results, showing that the theory satisfactorily predicts the primary dynamical and thermal properties of the storage tank.
M. Forestier, Pierre Haldenwang. Natural convection along a heated vertical plate immersed in a nonlinearly stratified medium: application to liquefied gas storage. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2007, 588, pp.217-241. <10.1017/S0022112007007458>. <hal-00907379>
Colette Nicoli, Pierre Haldenwang, Bruno Denet. Flame holding downstream from a co-flow injector. Comptes Rendus Mécanique, Elsevier Masson, 2006, 334, pp.408-413. Plus de détails...
We present numerical results on the flame attachment in the downstream vicinity of the co-flow injector lip that separates the reactive fluids at injection. Two stability diagrams show the domains where the flame is anchored, blown off, or extinguished, in terms of separating plate thickness and injection velocities of both fluids. Different anchoring modes—stagnation point counter-flow holding or edge flame anchorage—are described, depending particularly on the plate rim thickness.
Colette Nicoli, Pierre Haldenwang, Bruno Denet. Flame holding downstream from a co-flow injector. Comptes Rendus Mécanique, Elsevier Masson, 2006, 334, pp.408-413. <10.1016/j.crme.2006.06.002>. <hal-00091162>
Gilbert Accary, Isabelle Raspo. A 3D finite volume method for the prediction of a supercritical fluid buoyant flow in a differentially heated cavity. Computers and Fluids, Elsevier, 2006, 35 (10), pp.1316-1331. Plus de détails...
This paper describes a three-dimensional finite volume method for the prediction of supercritical fluid buoyant flows in heated enclosures. The space and the time accuracies of the method are checked on an exact analytical solution, and the solver is validated for several benchmark tests for natural convection inside a differentially heated cavity both in the Boussinesq and in the low Mach number approximations. Then, the influence of the linearization of the van der Waals equation of state on the global convergence is discussed. Comparisons, based on the Rayleigh number, between the supercritical fluid and the perfect gas flows in a side heated cavity, show many similarities in the thermal equilibria and considerable differences in the transient behaviours.
Gilbert Accary, Isabelle Raspo. A 3D finite volume method for the prediction of a supercritical fluid buoyant flow in a differentially heated cavity. Computers and Fluids, Elsevier, 2006, 35 (10), pp.1316-1331. <10.1016/j.compfluid.2005.05.004>. <hal-00834137>
Colette Nicoli, Pierre Haldenwang, S. Suard. Analysis of pulsating spray flames propagating in lean two-phase mixtures with unity Lewis number. Combustion and Flame, Elsevier, 2005, 143 (3), pp.299-312. Plus de détails...
Pulsating (or oscillatory) spray flames have recently been observed in experiments on two-phase combustion. Numerical studies have pointed out that such front oscillations can be obtained even with very simple models of homogeneous two-phase mixtures, including elementary vaporization schemes. The paper presents an analytical approach within the simple framework of the thermal-diffusive model, which is complemented by a vaporization rate independent of gas temperature, as soon as the latter reaches a certain thermal threshold (θv in reduced form). The study involves the Damköhler number (Da), the ratio of chemical reaction rate to vaporization rate, and the Zeldovich number (Ze) as essential parameters. We use the standard asymptotic method based on matched expansions in terms of 1/Ze. Linear analysis of two-phase flame stability is performed by studying, in the absence of differential diffusive effects (unity Lewis number), the linear growth rate of 2-D perturbations added to steady plane solutions and characterized by wavenumber k in the direction transverse to spreading. A domain of existence is found for the pulsating regime. It corresponds to mixture characteristics often met in air-fuel two-phase systems: low boiling temperature (θv≪1), reaction rate not higher than vaporization rate (Da<1, i.e., small droplets), and activation temperature assumed to be high compared with flame temperature (Ze⩾10). Satisfactory comparison with numerical simulations confirms the validity of the analytical approach; in particular, positive growth rates have been found for planar perturbations (k=0) and for wrinkled fronts (k≠0). Finally, comparison between predicted frequencies and experimental measurements is discussed.
Colette Nicoli, Pierre Haldenwang, S. Suard. Analysis of pulsating spray flames propagating in lean two-phase mixtures with unity Lewis number. Combustion and Flame, Elsevier, 2005, 143 (3), pp.299-312. <10.1016/j.combustflame.2005.06.008>. <hal-00907398>
Christophe Nicolas, Evelyne Neau, Sofiane Meradji, Isabelle Raspo. The Sanchez-Lacombe lattice fluid model for the modeling of solids in supercritical fluids. Fluid Phase Equilibria, Elsevier, 2005, 232 (1-2), pp.219-229. Plus de détails...
The Sanchez-Lacombe equation of state is known to describe the thermodynamic properties of molecular fluids of arbitrary size, especially polymer-solvent phase behavior. However, it is rarely used for modeling solid-supercritical fluid equilibria. In this work, it is shown that a proper estimation of the EoS characteristic parameters together with a thermodynamically consistent expression of fugacity coefficients allows a satisfactory correlation of the solubility of solids in the supercritical phase. Binary mixtures containing carbon dioxide, ethane, ethylene and xenon were considered for this purpose. In a first step, the consistency of experimental data was checked using variance analysis. Then, different mixing rules were considered and results compared with those obtained with the Peng-Robinson equation. Finally, the lower and upper boundaries of the solid-liquid-vapor regions (LCEP and UCEP) were also determined and compared with experimental values.
Christophe Nicolas, Evelyne Neau, Sofiane Meradji, Isabelle Raspo. The Sanchez-Lacombe lattice fluid model for the modeling of solids in supercritical fluids. Fluid Phase Equilibria, Elsevier, 2005, 232 (1-2), pp.219-229. <10.1016/j.fluid.2005.03.015>. <hal-00846093>
S. Suard, Pierre Haldenwang, Colette Nicoli. Different spreading regimes of spray-flames. Comptes Rendus Mécanique, Elsevier Masson, 2004, 332 (5-6), pp.387-396. Plus de détails...
We present a minimal model of spray combustion to investigate a flame front propagating through a fuel-lean mixture of fuel vapor, droplets and air. The model relies on a main control parameter, Da, named the Damkoehler number, which allows us to take into account a large variety of fuel sprays. Numerical results reveal, as a function of Da, a wide range of spray-flame structures, including the classical gaseous premixed flame, a specific regime controlled by vaporisation, and a pulsating mode of propagation. The latter appears when the vaporisation is smaller than (or equal to) the reaction time, and it occurs even with a unit Lewis number.
S. Suard, Pierre Haldenwang, Colette Nicoli. Different spreading regimes of spray-flames. Comptes Rendus Mécanique, Elsevier Masson, 2004, 332 (5-6), pp.387-396. <10.1016/j.crme.2004.02.004>. <hal-00907403>
Isabelle Raspo, E. Crespo del Arco. Instability in a rotating channel-cavity system with an axial through-flow. International Journal of Heat and Fluid Flow, Elsevier, 2003, 24 (1), pp.41-53. Plus de détails...
This paper is devoted to the numerical study of time-dependent flows that develop in a Taylor-Couette-like configuration (the outer cylinder exhibiting a side cavity) with a superposed axial through-flow, which is relevant to turbomachinery applications. Depending on the differential rotation rate between the inner cylinder and the cavity walls, the base flow can be either convectively or absolutely unstable, and then wave packets consisting of several small toroidal vortices appear near the inner cylinder and travel downstream. The influence of the different control parameters and of the inlet condition on the occurence of the patterns is analyzed. The flow simulations were obtained by using a spectral approximation coupled with a domain decomposition method for the solution of the axisymmetric time-dependent Navier-Stokes equations in the vorticity-streamfunction formulation.
Isabelle Raspo, E. Crespo del Arco. Instability in a rotating channel-cavity system with an axial through-flow. International Journal of Heat and Fluid Flow, Elsevier, 2003, 24 (1), pp.41-53. <10.1016/S0142-727X(02)00193-5>. <hal-00846032>
Journal: International Journal of Heat and Fluid Flow
Isabelle Raspo. A direct spectral domain decomposition method for the computation of rotating flows in a T-shape geometry. Computers and Fluids, Elsevier, 2003, 32 (3), pp.431-456. Plus de détails...
This paper presents a direct domain decomposition method, coupled with a Chebyshev collocation approximation, for solving the incompressible Navier-Stokes equations in the vorticity-streamfunction formulation. The method is based on the influence matrix technique used to treat the lack of vorticity boundary conditions on no-slip walls as well as to enforce the continuity conditions at the interfaces between adjacent subdomains. The multi-domain approach is proposed in order to extend the use of spectral approximations to non-rectangular geometries and singular solutions. It is applied to the computation of a four domain configuration, corresponding to a forced throughflow in a rotating channel-cavity system which is important in air cooling devices and cannot be modeled by single-domain spectral approximations.
Isabelle Raspo. A direct spectral domain decomposition method for the computation of rotating flows in a T-shape geometry. Computers and Fluids, Elsevier, 2003, 32 (3), pp.431-456. <10.1016/S0045-7930(01)00091-3>. <hal-00846076>
Colette Nicoli, Pierre Haldenwang, Bruno Denet. Combustion of gaseous co-flow jets. Combustion Science and Technology, Taylor & Francis, 2003, 175, pp.1143 - 1163. Plus de détails...
We present numerical results concerning the combustion that occurs in a three-plan jet system, which represents the two-dimensional version of a coflow gaseous injector of hydrogen and oxygen. The study focuses on the hydrodynamic effects--damped by combustion--that affect the high-speed jets at the entrance of a combustion chamber. The concerned parameters mainly involve the inlet flow velocities in a range where flame attachment occurs. The results confirm the classical idea according to which mixing-layer combustion damps shear-layer instabilities. Moreover, steady or unsteady solutions can be exhibited for the same set of parameters. For various ratios of density and inlet velocity (established between oxygen and hydrogen jets), we study the coflow dynamics (under combustion), which can be interpreted in terms of momentum flux ratio J. When increasing J, the dynamics become more and more complex, exhibiting large amplitude flapping, which produces the widening of time-averaged temperature field. For high J values, the dense oxygen jet is rapidly stripped and takes the same pattern as the liquid core observed in LOx injectors, with a dependence close to the Jm1/2 law measured for dense core length (albeit presently studied Reynolds numbers are one decade less).
Colette Nicoli, Pierre Haldenwang, Bruno Denet. Combustion of gaseous co-flow jets. Combustion Science and Technology, Taylor & Francis, 2003, 175, pp.1143 - 1163. <10.1080/00102200302346>. <hal-00091178>
Mohammed El Ganaoui, A. Lamazouade, Patrick Bontoux, Dominique Morvan. Computational solution for fluid flow under solid/liquid phase change conditions. Computers and Fluids, Elsevier, 2002, 31 (4-7), pp.539-556. Plus de détails...
A fixed grid method based on an enthalpy-porosity formulation for liquid/solid phase transition is extended to compute the time-dependent solutal convection in the melt during directional solidification of alloys. A finite volumes approximation is used for uniform and refined grids with a second order Euler scheme. The ability of the method to describe accurately the flow transitions and regimes is considered with respect to the results of the linear theory of stability and of available spectral accurate calculations.
Mohammed El Ganaoui, A. Lamazouade, Patrick Bontoux, Dominique Morvan. Computational solution for fluid flow under solid/liquid phase change conditions. Computers and Fluids, Elsevier, 2002, 31 (4-7), pp.539-556. <10.1016/S0045-7930(01)00067-6>. <hal-00838453>