Effect of various array structures on flow noise reduction

Abstract

Turbulent boundary layer pressure fluctuations can be reduced by filtering of its wave-number response with either a finite hydrophone or a hydrophone array, or by filtering the wave-number response through a layer of elastomer. In general practice, hydrophone arrays are embedded within a layer of elastomer to reduce the turbulent boundary layer pressure fluctuations and then mounted to an elastic structure. To understand the role of the mounting structure, this work will examine the performance of idealized and realistic array mounting configurations. Three configurations are modeled in this paper. The first one is a plane elastomer layer backed by a rigid surface. The second one is backed by an elastic plate with a finite thickness. Finally, the third one is backed by a layer of water. The front side of the elastomer layer is exposed to turbulent flow. The transfer functions for the three different configurations will be discussed. The results presented here are the numerically calculated noise reductions relative to the calculated noise level for a flush-mounted point hydrophone. In addition, an equivalent-plane-wave flow noise level is derived and compared among the three configurations to directly show any array performance similarities or differences.