The role of large-scale vortex in a turbulent jet noise

Abstract

In investigations of the role of large vortices in round turbulent Jet noise usually the case in point is mechanisms of radiation produced by collective movement of several vortex rings (pairing, tearing, etc.). The authors suggest to consider another radiation mechanism by which the mdividual vortex ring in a round jet can be an intensive sound source itself. Recent theoretIca and experimental investigations by the authors have shown that the total vortex ring noise consists of three components of similar frequencies but of different directivity. Each component, in its turn, is a stochastic process since it is generated by a large number of oscillations with different (though close) frequencies. So, the principal goal of the work is to “recognize” the individual vortex noise in the total noise of turbulent jet (or to demonstrate ineffectiveness of such a radiation mechanism in a real jet). Now we present the first results m this direction. The measurement procedure developed in the investigations of vortex ring noise and based on synchronous decomposition of signal from hexagon array of microphones with subsequent averaging is used for the analysis of low-speed round jet noise. A microphone array for recording was placed in the far sound field of the jet. Two cases are considered: (i) non-excited jet, (ii) jet excited by a sinusoidal signal. Measurements of nerodynanuc characteristics of jet and visualization were conducted before the acoustic measurements.