Sound propagation issues in compressible turbulence

A physical interpretation of the stabilizing effect of Mach number on free shear flows is offered. The hindrance of communication, caused by the Mach number, between regions in a shear flow is addressed and quantified in the limit of geometric acoustics. The sound emitted by an acoustic source, located inside a shear layer, is considered. Ray construction shows progressively larger distortions of the acoustic rays as the Mach number at the source location increases. Consequently, the influence of the source on the surrounding flow field diminishes, as revealed by computations of the sound intensity along the streamwise axis. It is proposed that the resulting poor communication among regions of the flow field leads to the inherent stability of compressible shear flows.