LES of turbulence and turbulent combustion: advances and theoretical limitations

摘要

Large Eddy Simulations account for the subgrid velocity fluctuations ina model (analytic) way. It is argued that due to small-scale intermittency, the LES models based on the Kolmogorov-Smagorinki phenomenology must fail for any mesh size #DELTA# when the Reynolds number is large enough and #DELTA# corresponds to the scales in the inertial range. Physically, the existing phenomenology treats very strong and weak fluctuations on the equal footing as governed by the single parameter (mean dissipation rate). This leads to unreasonably large overproduction of kinetic energy and, as a consequence, poor predictions. Intermittency disappears at the large scales and that is why the time-dependent VLES schemes are much more successfull in descibing hi Reynolds number flows. Various examples, presented in the paper support this point of view.