INVISCID INSTABILITY OF A SKEWED COMPRESSIBLE MIXING LAYER

In this paper we study the inviscid instability of a skewed compressib le mixing layer between streams of different velocity magnitude and di rection. The mean flow is governed by the three-dimensional laminar bo undary-layer equations and can be reduced to a sum of a uniform flow a nd a two-dimensional shear flow. In the stability analysis, the amplif ication direction is assumed to be normal to the homogeneous direction of the mean flow. The results show that skewing enhances the instabil ity by a factor of three for the incompressible mixing layer with velo city ratio 0.5 and uniform temperature. Under compressible conditions, skewing still increases the maximum amplification rate for a medium c onvective Mach number, but the enhancement is smaller. A scaling of th e skewing effect is introduced which quantitatively explains the linea r stability behaviour. Similarly, a suitably defined convective Mach n umber explains the compressibility effect.