ASA 125th Meeting Ottawa 1993 May

2aEA3. Wave-vector filtering and flow noise reduction in finite structures.

Y. F. Hwang

David Taylor Model Basin, Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000

It has been shown in the literature that the unwanted noise voltage output from a pressure sensing system due to the pressure fluctuations of a turbulent boundary layer can be minimized by exploiting the wave-number filtering action of finite hydrophones and hydrophone arrays, or by other wave-number filtering techniques. This paper discusses the similar effect in a finite structural panel subjected to the same excitation. However, in this case, the corresponding output is the effective modal force per unit area that excites the structural mode. The wave-number filtering characteristics of structural modes as a function of flow parameters, structural dimensions, mode order numbers, and boundary conditions are presented. The effective modal force per unit area is evaluated as the sum of contributions from three wave-number regions: the low-wave-number region, at and near the modal wave-number (within the major lobe) of a structural mode; the high-wave-number region, at and near the hydrodynamic coincident wave-number; and the intermediate wave-number region that lies between the above two regions. The relative contributions of the three wave-number regions are important criteria upon which further noise reduction strategies are devised. [Work supported by ONR.]