Abstract

The generation and radiation of noise from a rigid surface immersed in a turbulent flow field may be characterized by the strength of the dipolelike sources associated with the normal surface pressures acting on the fluid at the surface, and by the regions over which these sources are partially correlated. New frequency-domain expressions have been developed for the dipole source strength per unit area, based on mean-square pressure and acoustic intensity, and for the correlation area. The equations are similar to time-domain expressions developed earlier [T. E. Siddon, J. Acoust. Soc. Am. 53, 619–633 (1973)]. The equations show that the correlation area can be thought of as a complex radiation efficiency that is normalized by its maximum value, the total area of the surface immersed in turbulence. Both the correlation area and dipole source strength per unit area reflect the noise generation characteristics of the local turbulence regions and mutual interactions between regions. Results of experiments will be presented in which a single blade, removed from a rotating centrifugal air moving device, was immersed in a turbulent flow field.

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