THE GENERATION OF SOUND BY TURBULENT AND SEPARATED FLOWS

An overview is given of the mechanisms of sound generation by free-field turbulence and by vorticity interacting with a body, with particular reference to flews at low Mach number. The theory is illustrated by discussions of the periodic sound produced by a cylinder in a uniform stream (AE olian tones) and of the noise generated by turbulence flowing over the trailing edge of an airfoil. In the latter case consideration is also given to the influence of surface compliance: structural modes of vibration are excited by the edge-flow; in conditions of heavy fluid loading, which typically occur in underwater applications, the energy imparted to the structure leads to the generation of substantial levels of additional sound when ''surface waves'' are scattered at mechanical discontinuities.