FLOW NOISE TRANSMITTED THROUGH DOMES OR ACOUSTICALLY MODIFIED BY NON-RIGID BOUNDARIES
Interim progress rept.
CONTROL DATA CORP MELVILLE NY TRG DIV
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Flow-induced noise generated by pressure fluctuations in a turbulent boundary layer is studied here theoretically with regard to its acoustic transmission through a dome to a transducer element or array. Particular attention is given to a unilayer dome in the form of a finite slab, described as a fluid but serving as a prototype for a realizable solid slab. A similar dome with a thin outer cover having nonvanishing impedance is also considered. Likewise, attention is given to acoustic modification of the flow noise on a flush element due to mobility of the surrounding baffle. To demonstrate clearly what properties of the boundary layer pressure fluctuations are essential, high- and low-wavenumber ranges are distinguished in the wavenumber spectrum of pressure at given frequency, the former range corresponding to possible generation by a convected eddy field. By various approximations and simplification of boundary conditions, the contributions of these respective ranges to the frequency spectrum of average pressure on a dome-shielded element are related to their respective contributions in the reference case of an element flush-mounted in a rigid plate.
- Acoustic Detection and Detectors
- Fluid Mechanics