MACH WAVE EMISSION FROM A HIGH-TEMPERATURE SUPERSONIC JET

The paper considers the compressible Rayleigh equation as a model for the Mach wave emission mechanism associated with high-temperature supe rsonic jets. Solutions to the compressible Rayleigh equation reveal th e existence of several families of supersonically convecting instabili ty waves. These waves directly radiate noise to the jet far field. The predicted noise characteristics are compared to previously acquired e xperimental data for an axisymmetric Mach 2 fully pressure balanced je t (i.e., P(e)/P(a) = 1.0) operating over a range of jet total temperat ures from ambient to 1370 K. The results of this comparison show that the first-order supersonic instability wave and the Kelvin-Helmholtz f irst-, second-, and third-order modes have directional radiation chara cteristics that are in agreement with observed data. The assumption of equal initial amplitudes for all of the waves leads to the conclusion that the flapping mode of instability dominates the noise radiation p rocess of supersonic jets. At a jet temperature of 1370 K, supersonic instability waves are predicted to dominate the noise radiated at high frequency at narrow angles to the jet axis.