THE STABILITY OF COMPRESSIBLE MIXING LAYERS IN BINARY GASES

We present the results of a study of the inviscid two-dimensional spat ial stability of a parallel compressible mixing layer in a binary gas. The parameters of this study are the Mach number of the fast stream, the ratio of the velocity of the slow stream to that of the fast strea m, the ratio of the temperatures, the composition of the gas in the sl ow stream and in the fast stream, and the frequency of the disturbance wave. The ratio of the molecular weight of the slow stream to that of the fast stream is found to be an important quantity and is used as a n independent variable in presenting the stability characteristics of the flow. It is shown that differing molecular weights have a signific ant effect on the neutral-mode phase speeds, the phase speeds of the u nstable modes, the maximum growth rates, and the unstable frequency ra nge of the disturbances. The molecular weight ratio is a reasonable pr edictor of the stability trends. We have further demonstrated that the normalized growth rate as a function of the convective Mach number is relatively insensitive (approximate to 25%) to changes in the composi tion of the mixing layer. Thus, the normalized growth rate is a key el ement when considering the stability of compressible mixing layers, si nce once the basic stability characteristics for a particular combinat ion of gases is known at zero Mach number, the decrease in growth rate s due to compressibility effects at the larger convective Mach numbers is somewhat predictable. (C) 1996 American Institute of Physics.