A stability study of the developing mixing layer formed by two supersonic laminar streams

An inviscid, parallel, spatial linear stability analysis is performed on both bounded and semibounded developing mixing layers formed between a laminar Mach 8 stream and another at Mach 3. Three unstable modes have been found in the initial mixing zone of the unbounded flow. In the downstream region of this flow the slowest of these modes becomes stable, and the remaining two correspond to the fast and slow modes of the self-similar mixing layer. For the semibounded flow, a wall in the slow stream introduces a series of acoustic modes which replace the fast mode of the unbounded how. For both the unbounded and the semibounded flows the largest growth rates belong to the slowest mode which resides in the developing region and is insensitive to the presence of the wall. The existence of this mode has been detected in a wind-tunnel experiment, at frequency ranges suggested by, and with maximum growth rates in agreement with, the theory. (C) 1996 American Institute of Physics.