Résumé: The Lagrangian and Eulerian acceleration statistics in homogeneous
turbulence with uniform shear and stratification are studied using
direct numerical simulations. The Richardson number is varied from Ri =
0, corresponding to unstratified shear flow, to Ri = 1, corresponding to
strongly stratified shear flow. The probability density functions
(pdfs) of both Lagrangian and Eulerian accelerations show a strong and
similar influence on the Richardson number and extreme values for
Eulerian acceleration are stronger than those observed for the
Lagrangian acceleration.
Similarly, the Eulerian time-rate of change
of fluctuating density is observed to have larger extreme values than
that of the Lagrangian time-rate of change. Hence, the time-rate of
change of fluctuating density obtained at a fixed location by an
Eulerian observer is mainly due to advection of fluctuating density
through this location, while the time-rate of change of fluctuating
density following a fluid particle is substantially smaller, and due to
production and dissipation of fluctuating density.
(Château Gombert IMT La Jetée, 2ème étage)
