Inferring large-scale wall-pressure sources in turbulent boundary layers using space–time correlations

Wall-pressure fluctuations (p_w) beneath turbulent boundary layers (TBL) drive structural loading and flow-induced noise. Yet little is known, particularly regarding its outer-scaled sources that grow with friction Reynolds number (Re). This study finds that dominant outer-scaled p_w sources coexist from the near-wall up to the top of the logarithmic region, where the mean velocity matches the convection speed of the large-scale p_w signature. This finding was inferred from experimental data, acquired using a 63-microphone array that spans across five TBL thicknesses in the streamwise direction, capturing space-time p_w data synchronously with streamwise velocity data from a hotwire. The array was designed to measure the spatially-filtered p_w, to ensure that the large-scale portion of the frequency–wavenumber p_w-spectrum was resolved without effects of aliasing the small-scale energy content. Measurements at low-to-moderate Re (1400 < Re < 5200) revealed a growth in the wall-pressure–velocity correlations across the inner region, with contours at the top of the log region being reminiscent of the very-large-scale motions. Our findings provide new insights concerning the use of wall-pressure in modeling and control attempts of high-Re wall turbulence.