Surface pressure fluctuations beneath two- and three-dimensional turbulent boundary layers

Surface pressure fluctuation measurements were made in two-dimensional turbulent boundary layers at two Reynolds numbers (Re-theta = 7.3 X 10(3) and 2.34 X 10(4)) and pressure-driven three-dimensional turbulent boundary layers at two Reynolds numbers (approach Re-theta = 5.94 X 10(3) and 2.32 X 10(4)). The collapse of spectral levels at middle and high frequencies and the effects of inner and outer boundary-layer scaling variables are shown for a wide range of Reynolds numbers (1.4 X 10(3) < 2.34 X 10(4)) for the two-dimensional flows. Such scaling parameters do not collapse the pressure spectra beneath three-dimensional hows, which have a nearly constant, or flat, midfrequency range, and at some measurement stations and spectral levels within the flat- and high-frequency spectral ranges that significantly raise p'. Additionally, dimensional spectral levels within the Bat-frequency range are independent of Reynolds number. Analysis based on the Poisson equation shows that the variation of the high-frequency spectral levels is related to the variation in near-wall mean velocity gradients and nu(2) structure due to the spanwise pressure gradient.