THE EFFECT OF SOLID-SURFACES ON TURBULENT JET NOISE

Lighthill's acoustic analogy is applied to the problem of calculating the sound radiated by unit volume of jet-type shear-layer turbulence n ear a solid surface. The ensemble-averaged basic directivity patterns of the sound generated by randomly orientated longitudinal and lateral quadrupoles near a rigid plane are calculated, and are found to be ve ry different for the two types of quadrupole. A method of modelling th e acoustic sources, due to Ribner, is extended to the present case, en abling the basic directivity pattern to be calculated. The effect of t he solid surface is found to depend strongly on the source frequency, and a method for estimating the source frequency in an actual turbulen t shear flow is developed. The theory is applied to a plane two-dimens ional wall jet, and predictions of some basic aero-acoustic characteri stics are obtained. (C) 1995 Academic Press Limited