Further Topics in Aerodynamic Noise

Abstract

In principle, the convected quadrupole theory, as developed by Ffowcs-Williams, can be used also for supersonic jet noise. However, subsonic jet noise, where no complex phenomena such as shock or screeching noise exist, is based mainly on turbulent mixing. Supersonic jet noise, on the other hand, “is a cumulative effect of Mach wave radiation, nozzle tip radiation, nozzle lip radiation, shock turbulence interaction, shock unsteadiness and turbulent mixing” [65]. Mach waves, generally for supersonic, fully expanded nozzles, are mainly due to disturbance-convected, supersonically radiating sound in a highly directional peak and originating in a region of a few jet diameters from the nozzle exit. For supersonic over- or underexpanded nozzles, noise is produced by turbulence shock interactions, and it occurs at highly discrete frequencies.