Application of elastomeric material to the reduction of turbulent boundary layer pressure fluctuations

Abstract

Turbulent boundary layer pressure fluctuations can be reduced by either spatial filtering through the use of a finite hydrophone or a hydrophone array or by filtering through direct path attenuation. In general practice, various configurations of hydrophone arrays are embedded within a layer of elastomer, thus reducing the turbulent boundary layer pressure fluctuation. The direct path attenuation depends on the elastomer layer thickness, the shear wave speed, and the loss factor associated with the shear wave in the elastomer layer. In the filtering process, the mechanism that controls the direct path attenuation is most important. The theoretical model considered in this paper is a plane elastomer layer backed by an infinite plate with finite thickness; the other side of the layer is exposed to turbulent flow. A theoretical analysis is presented for the development of the transfer function that determines the amount of direct path attenuation. The results presented are numerically calculated transfer functions and noise reductions for various parameters related to direct path attenuation.