ASA 125th Meeting Ottawa 1993 May

2aEA2. Fundamentals of outer decoupler design for flow noise reduction.

Nathan C. Martin

Bolt Beranek and Newman, Inc., 70 Fawcett St., Cambridge, MA 02138

Turbulent boundary-layer (TBL) wall-pressure fluctuations due to the flow of water over a sonar array produces significant levels of array self-noise. This flow noise background reduces the ability of the array to detect acoustic waves propagating from distant sources. These flow noise levels can be reduced by various methods including hydrophone area averaging and the separation of the array from the flow interface by structures generically referred to as outer decouplers. Examples of outer decouplers (O.D.) include sonar domes and elastomer-covered arrays. The fundamental objective of outer decoupler design is to provide a low pass filter in wave number k. Analytic modeling of the structural acoustic behavior of O.D. structures provides a basis for both understanding the wave-number filtering process and designing effective O.D.'s for specific applications. This paper reviews the basic structural acoustics of various O.D. classes to illustrate the differences in wave-number filtering performance at various frequencies and the application of these filter characteristics to array flow noise reduction. [Work supported by Office of Naval Research.]