Sound Generation by Turbulent Wall Jet Flow over a Trailing Edge

Abstract

A method for predicting the amount and directivity of sound generated by turbulent flow over a trailing edge was developed for the case where the acoustic wavelength is less than the characteristic dimensions of the surface. This case is important for sound radiated by flow over surfaces such as large fan blades. An analytical and experimental study is presented using for a flow model a turbulent wall jet. The wall jet had three different flow regions exhibiting behavior like a turbulent boundary layer, two-dimensional turbulent flow, and radial type or three-dimensional turbulent flow, respectively. Application of Curle's solution for sound radiated by a distribution of pressure over a rigid surface is extended to the case where a trailing edge exists. A similarity model is given relating the sound power to mean flow parameters. The diffraction of the dipole sound by the edge was analyzed and measured. The maximum acoustic intensity was found to be along the plate in contrast to the free-field dipole, which has minima in that plane.