Curved flames beyond Markstein’s relationship : experimental results / 2016

Le jeudi 12 Mai 2016 à 11h, dans l’amphithéâtre du M2P2 (à Château Gombert)

Pr. Pedro Garcia-Ybarra

Facultad de Ciencias, UNED - Madrid

Laminar jet flames display an axisymmetric concave configuration where the increase of local burning velocity by flame compression (negative stretch) leads to robust flame tips which can withstand gas blowing velocities several times larger than the planar flame burning velocity. The aim of this work was to carry out a study at the region around the tip of strongly curved flames, where the classical linear relation between local flame burning velocity and flame stretch [1] is no longer applicable and is expected to be replaced by some nonlinear relation. We have set up an experiment where the local values of the burning velocity and of the curvature have been simultaneously measured along the front of a jet flame [2, 3]. This has allowed us to experimentally determine the planar flame propagation velocity and the Markstein length, as well as to assess the validity of the linear relation at any point of the flame front, from the quasi-conical skirt to the rounded tip. It turns out that the Markstein relation is not enough to give a full satisfactory account of the experimental data because it does not reproduce the departure from the linear behavior observed experimentally, nor the multivaluedness of the burning velocity for the same values of the stretch in flames with different heights (corresponding to different blowing velocities of the feeding gas). To account for the observed non-linear behavior, it seems natural to extend the linear relation to include a term quadratic in the stretch which should contain essentially the dependence on the gas blowing velocity.

[1] P. Garcia-Ybarra, C. Nicoli, P. Clavin, Combus. Sci. Technol. 42 (1984) 87–109.
[2] G. Garcia-Soriano, P.L. Garcia-Ybarra, F.J. Higuera, Flow Turbul. Combust. 89 (2012) 173–182.
[3] G. Garcia-Soriano, J.L. Castillo, F.J. Higuera, P.L. Garcia-Ybarra, C. R. Mecanique 340 (2012) 789–796.