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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Measurements of aerodynamic noise, in the form of pressure fluctuations in a turbulent boundary layer, were made on a smooth flat plate in the 12- and 20-in. supersonic wind tunnels at the Jet Propulsion Laboratory. The noise was measured with small piezoelectric pressure transducers (0.015-0.03 in. diameter) constructed of barium titanate crystals which were flush-mounted in the flat plate. Spectral-energy distributions of the pressure fluctuations are obtained up to a frequency of 0.5 mc at freestream Mach numbers from 2.0 to 5.0, and Reynolds numbers based an bound layer-displacement thickness from 5 x 10(3) to 5 x 10(4). By grouping the test variables into the proper nondimensional forms and correcting for the finite transducer size, the energy spectra are found to be similar and uniquely related to both Mach number and Reynolds number. The total, or integrated, level of noise at the plate surface, in terms of root-mean-square values of the pressure fluctuations, is a constant equal to about 10 times the shear stress [...] the wall. The intensity, [...], is directly proportional to the fourth power of the freestream Mach number. Correlation measurements in time and in the streamwise direction in space show that the noise at the plate surface to convected downstream with a characteristic velocity equal to 75% of the freestream velocity. The correlation dies off rapidly with spacing between pickup points, and the convection velocity shows no dependence on either Mach number or Reynolds number. |
