Structure and Noise of a Supersonic Jet Under Internal Acoustic Excitation

Abstract

Introduction T HE acoustic excitation of turbulent jets as a method of study and a means of affecting their aerodynamic and acoustic characteristics and coherent structures is the subject of a number of theoretical and experimental investigations. In such works a sinusoidal excitation of small intensity is used, as a rule, and the subject of studies is a subsonic jet. The effect of multifrequency acoustic excitation on subsonic jets was also investigated, and a certain number of works deal with the effect of high-intensity sound on jets.1 As it is believed, the effect of small-intensity sound on subsonic jets with Reynolds number Re 105 can be only amplified under sound excitation,2 and of reducing the supersonic jet noise.3 The proper jet shockwave structure can essentially vary in this case, and appearance of the compact hydrodynamic disturbances can be accompanied by Mach wave radiation at the external excitation frequency, if their convective velocity exceeds the ambient sound velocity.4 The internal longitudinal excitation of turbulent jets with Reynolds number Re > 105 leads to increasing the noise radiated by the jet,5 but at the present time the mechanism of such an effect and its influence on supersonic jet structure remains unclear in many aspects. The purpose of the present work is to investigate the effect of the longitudinal internal high-intensity sound excitation on a cold supersonic air jet structure and noise.