Wall pressure fluctuations and flow induced noise in a turbulent boundary layer over a bump

Abstract

A direct numerical simulation is performed to examine the relationship between wall pressure fluctuations and near-wall streamwise vortices in a spatially developing turbulent boundary layer. It is found that wall pressure fluctuations are closely linked with the upstream quasistreamwise vortices in the buffer region. The maximum correlation occurs with the spanwise displacement from the location of wall pressure fluctuations. The space-time correlation reveals that wall pressure fluctuations lag behind streamwise vorticity in the upstream, while streamwise vorticity lag behind wall pressure fluctuations in the downstream. The contributions of high-amplitude wall pressure event to the turbulent energy production mechanism are examined by the quadrant analysis of Reynolds shear stress. A direct numerical simulation of a spatially developing turbulent boundary layer is performed to examine the characteristics of wall pressure fluctuations after the sudden application of wall blowing or suction. The uniform blowing or suction is given by the wall-normal velocity through a spanwise slot at the wall. The response of wall pressure fluctuations to uniform blowing or suction is analyzed by computing the turbulence statistics and frequency spectra. It is found that wall pressure fluctuations are more affected by blowing than by suction. The large elongated structure of wall pressure fluctuations is observed near the maximum location of $(Pw)_{rms}$ for blowing. The convection velocities for blowing increase with increasing the streamwise location after the slot. For both blowing and suction, the small scale of wall pressure fluctuations reacts in a short downstream distance to the spanwise slot, whereas the large scale recovers slowly farther downstream. A direct numerical simulation of a turbulent boundary layer over a bump were performed to examine the effects of surface longitudinal curvature on wall pressure fluctuations. Turbulence statistics and frequency spec...