Large Eddy Simulations of Shear Flows: Mixing Layers

Abstract

The computation of shear flows has moved into the field of interest not only of fundamental research but also of industrial applications, especially aircraft propulsion devices. Numerical simulations of mixing layer are performed here, using a code specifically developed for gaseous turbulent flows (Gathmann et al., 1993) which can moreover take account of chemical reactions. The supersonic shear layer is of central interest within the framework of supersonic propulsion systems. The shear layer can be regarded as a simple model of injection device of fuel into an air stream. The instability of a compressible shear layer was investigated by some authors in terms of linear stability theory applied to a 2D vortex sheet. The unconfined shear layer was shown to be stable to 2D disturbances for supersonic convective Mach numbers M c > 1. Three dimensional numerical simulations already published by various authors assumed a temporal approximation, that is a periodicity in the streamwise direction. However, such a periodicity limits the study to modes whose length waves are a multiple of the fundamental wave number specified by the length of the computational domain. We have investigated a spatially developing supersonic mixing layer confined between rigid walls at convective Mach number M c = 1.8 by numerical simulations in 2D and 3D (Gathmann et al, 1993).