DNS Study of Supersonic Mixing Layers

Abstract

Direct numerical simulation is used to investigate three-dimensional temporal supersonic mixing layers at two convective Mach numbers 1.2 and 1.6. At Mach number of 1.2, the compressibility effects, characterized by the shear layer growth rate reduction, are more pronounced than at high subsonic convective Mach numbers. In this case, the structure of flow becomes three-dimensional, and Λ structures are clearly observed which accelerate the occurence of turbulence. For the M _c = 1.2 case, the absence of symmetry leads to a strong interaction between a Λ structures. At M _c = 1.6, the use of a computational box the size of one fundamental wavelength maintains the symmetry of the flow. The Λ structures, strongly inclined, are distorted by the shear layer and split into two symmetrical parts. Finally, shocklets occur in the flow for both convective Mach numbers. These viscous shocks are developed in three-dimensions and are stronger for the 1.6 case. In this paper transition mechanisms are analyzed and the existence of shocklets and their influences are studied.