Noise Radiated from an Edge in Turbulent Flow

Abstract

An evanescent-wa ve formulation relates sound radiated from subsonic turbulent flow at the edge of a semiinfinite rigid surface to a wavevector-frequency spectral density P(K,u>) of hydrodynamic pressure. This has been used to obtain the frequency spectra of nearfield pressure in the surface and of farfield radiated pressure and the cross-spectrum between them. A model differing from those used previously is suggested for P(K,u>) to fit the frequency dependence of nearfield (and radiated) pressure spectra measured in jet-flow experiments and is interpreted to indicate dominance by the mean-shear source term. Results are applied to a recent experiment where a jet streamed off a flat surface. With model parameters determined mainly from nearfield surface pressure spectra, the predicted radiated spectrum agrees well with that measured. The measured crosscorrelations between nearfield and radiated pressure plotted vs edge distance from the nearfield point at different frequencies roughly coalesce when normalized in accord with a predicted universal form and agree adequately with the result of the model. Significant validation of the method and of the proposed characterization of hydrodynamic pressure is thus obtained for the given flow configuration. Extension to two-sided flows is discussed.