Turbulent wall pressure fluctuations over wavy surfaces

Abstract

Measurements of the spectral characteristics of the wall /2 pressure fluctuations produced by a turbulent boundary layer flow U~ over solid sinusoidal surfaces of moderate wave amplitude to waveu* length ratios have been obtained. The wave amplitudes were suffix ciently small so that the flow remained attatched. The results show y that the root mean square pressure level reaches a maximum on the z adverse pressure gradient side of the wave at a position somewhat ct + before the trough. Spectral analysis of the pressure fluctuations in narrow frequency bands reveals considerable differences in low and fl 6* high frequency behavior. At low frequencies, the peak fluctuation Flo, ~ amplitude was found at the trough whereas at high frequencies, the peak occurs just after the crest and a minimum is found at the Ft"t trough. Pressure fluctuations having streamwise correlation lengths v on the order of or larger than the wavelength of the surface do not return to their equilibrium (crest) amplitudes as they travel the co length of a wave. Pressure fluctuations having streamwise correlation lengths about one order of magnitude less than a wavelength ~b~ return exactly to their equilibrium amplitudes. Two-point correlation measurements show a decrease in longitudinal coherence on the T "C w adverse pressure gradient side of the wave at low frequencies and a 0 considerable increase over a broad frequency range on the positive pressure gradient side. No change is found in the lateral coherence.