Reynolds number dependence of wall-pressure fluctuations in weakly compressible turbulent channel flow

Compressible direct numerical simulations are employed to examine the Reynolds number dependence of the spatiotemporal characteristics of wall-pressure fluctuations in weakly compressible turbulent channel flow. Simulations are conducted at a bulk Mach number of 0.4 and friction Reynolds numbers of 180, 500, and 1000. With increasing Reynolds number, the results show a significant growth in the spectral level in the subconvective wavenumber range, as well as an elevation and broadening of the convective ridge, particularly at higher frequencies. At the low friction Reynolds number of 180, acoustic peaks are barely visible in the one-dimensional streamwise wavenumber-frequency spectrum. However, at higher Reynolds numbers, acoustic peaks associated with longitudinal and oblique waves emerge in the subconvective wavenumber range, accompanied by a broadband rise in spectral levels. The Reynolds number effect on acoustic ridges is most prominently displayed in the two-dimensional wavenumber-frequency spectra at the zeroth spanwise wavenumber, and the use of inner scaling for normalization is found to largely account for this effect in both convective and subconvective wavenumber ranges.