Noise generated by axisymmetric turbulent boundary-layer flow

Abstract

The noise generated by hydrodynamic flow over an axisymmetric body with a blunt noise is described quantitatively. Flush-mounted piezoceramic hydrophones were used to measure that part of the turbulent boundary-layer pressure fluctuations that propagates as true sound. Power spectra of the sound pressure were measured in a 3–50-kHz frequency range over a wide range of Reynolds numbers (U∞D/ν?3.03×106, where D is the diameter of the body) for the model operating in the Garfield Thomas water tunnel. The use of flush-mounted hot-film probes to locate turbulence transition is also described. The power spectra of the noise measured in the laminar flow regions correspond closely to those measured in the transition and fully developed turbulent regions of the flow. The exceptions were those spectra measured on the flat part of the nose, but correction for diffraction-loss effects suggests that the noise measured there is due to the noise generated by the turbulent part of the flow. Nondimensionalization of the noise spectra measured at various arc lengths with theoretical expressions for the noise expected, that include a critical boundary-layer thickness at the beginning of turbulence, show a general collapse of data to within 6 dB. When applicable, comparisons of the radiated noise measured on buoyant bodies are made and agreement was found to be excellent.