Abstract:

A theoretical model was developed to evaluate flow noise levels received by a velocity sensor that is embedded within an outer decoupler mounted on a low acoustic impedance surface. The model, a three-layer structure, consists of a layer of nonvoided elastomer (outer decoupler), which covers a layer of microvoided elastomer (inner decoupler) backed by an elastic plate. The rubberlike material of the outer decoupler is designed to reduce the flow noise generated by turbulent boundary layer pressure fluctuations, and the low acoustic impedance (soft) material of the inner decoupler is configured to reduce the flexural wave noise generated by the vibration of the elastic plate. The upper surface of the outer decoupler is in contact with turbulent flow (water) and the lower surface of the backing plate is in contact with semi-infinite space (air). This work uses the model of the three-layer composite structure for the analyses of both the flow noise and signal levels received by the embedded velocity sensor. The final noise levels are the equivalent plane-wave levels, which were obtained by subtracting the signal levels from the flow noise levels. [Work supported by the Office of Naval Research, Code 321SS.]