Near-Field Shocks Radiated by High-Speed Free-Shear-Flow Turbulence

Temporally developing turbulent planar free shear layers with Mach numbers M = 1.5, 2.5, and 3.5 are directly simulated to provide a geometrically simplified model of the generation of a peculiar sound, known as ‘crackle’. Sound-field pressure skewness for M = 2.5 and 3.5 cases exceed Sk(p ′) > 0.4, which has been correlated with perception of crackle. Statistics related to Mach wave angle and wave density indicate nonlinear interactions in the very near acoustic field in these same cases. Results show both merging of multiple waves and flattening of non-planar waves into approximately planar weak shocks.

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