CHARACTER OF MACH WAVE RADIATION AND CONVECTION VELOCITY ESTIMATION IN SUPERSONIC SHEAR LAYERS

The nature of acoustic radiation from mixing layers at high compressibility conditions is studied. Strong acoustic waves are generated by slow moving large-scale turbulent structures over a wide range of convective Mach numbers and density ratios. Strong waves and curved shocks associated with large disturbances are seen over a limited density ratio and compressibility range. Convection velocities are estimated by measuring the local Mach wave angle radiating from the disturbance but do not appear to follow the stream selection rule. For Mc < 2, the convection velocity favors the low speed velocity in all cases. Evidence of co-layer behavior at Mc = 2.84 is apparent from dual measured convection velocities. Behavior of curved, strong shocks in a time sequence image shows shock waves anchored to the leading edge of structures and external to the shear layer, rather than embedded as eddy shocklets.

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