On the radiation of sound by the instability waves of a compressible axisymmetric jet.

A solution for the acoustic radiation generating by the instability waves of a compressible axisymmetric jet is reported. The decription of the instability wave in the jet flow and close to the edge of the jet is constructed using the method of multiple scales. This solution accounts for the effects of the slightly divergent mean flow. The multiple scales expansions is shown to be not uniformly valid far from the jet. A method for continuing this solution into the acoustic far field is described. Calculations of near and far field pressure fluctuations are presented for an unheated, ideally expanded, axisymmetric jet with exit Mach number 1.5, and are compared with the measured pressure levels. The naturally occurring excitation levels of the instability waves are estimated. (A)