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 θ = 7.3 × 10 3 and 2.34 × 104) and pressure-driven three-dimensional turbulent boundary layers at two Reynolds numbers (approach Re θ = 5.94 x 10 3 and 2.32 × 104). 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 × 104) for the two-dimensional flows. Such scaling parameters do not collapse the pressure spectra beneath three-dimensional flows, 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 flat-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 ν 2 structure due to the spanwise pressure gradient