Reynolds Number Effect on Wall-Pressure Fluctuations in Low-Mach-Number Turbulent Channel Flow

The effect of Reynolds number on the spatiotemporal characteristics of wall-pressure fluctuations in turbulent channel flow is investigated using compressible direct numerical simulations at a bulk Mach number of 0.4 and friction Reynolds numbers of 180, 500 and 1000, with an emphasis on the subconvective wavenumber range. At the low friction Reynolds number of 180, acoustic peaks are barely visible in the one-dimensional streamwise wavenumber--frequency spectrum. However, as the Reynolds number increases, acoustic peaks corresponding to longitudinal and oblique waves emerge at subconvective wavenumbers, accompanied by a broadband rise in spectral levels. The impact of Reynolds number on acoustic ridges is more prominent in the two-dimensional wavenumber--frequency spectrum at the zeroth spanwise wavenumber, where acoustic peaks become significantly stronger with increasing Reynolds number. The use of inner scaling for normalization can largely account for the Reynolds number effect in both convective and subconvective wavenumber ranges.