Surface Pressure Spatial Cross-Spectra Beneath High-Reynolds-Number Boundary Layer Flows

The spatial cross-spectra of surface pressures beneath turbulent boundary layer flows with friction Reynolds numbers ranging from approximately 4,000 up to 80,000 were experimentally characterized in multiple facilities. Measurements were performed in a large water tunnel to achieve friction Reynolds number greater than 15,000, and wind tunnel tests were performed to characterize the surface pressure fluctuations for flows with Reynolds numbers less than 7,000. In both sets of tests, arrays of individual pressure sensors were embedded into the flow surface to measure the multi-point pressure cross-spectra. Mean velocity profiles were measured to characterize the boundary layer flow parameters. The measurements revealed that the surface pressure coherence spectra for streamwise separations exhibit a slower frequency roll-off rate with increasing Reynolds number, which indicates that the pressure levels in the sub-convective wavenumber range decrease with increasing Reynolds number. An empirical model, based on the Modified Corcos function, was developed to describe the measured spatial coherence of the surface pressure fluctuations over the wide measured range of Reynolds numbers, which showed a faster roll-off rate of coherence than is predicted by the 1987 Chase model.