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 spectra were examined to elucidate the response of wall pressure fluctuations to the longitudinal curvature and to the corresponding pressure gradient. Wall pressure fluctuations were significantly enhanced near the trailing edge of the bump, where the boundary layer is subjected to a strong adverse pressure gradient. Large-scale structures in the wall pressure fluctuation distribution were observed to grow rapidly near the trailing edge of the bump and convect downstream. In addition, the distance between the streamwise vortices and the wall increased slightly near the trailing edge of the bump. This caused the magnitude of the streamwise vorticity to increase significantly due to the diminishing of the interaction with the wall, leading to an enhancement of the wall pressure fluctuations.
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 and flow induced noise. Acoustic sources of the Lighthill equations are investigated in detail with the variations of longitudinal surface curvature. Acoustic density fluctuations at far-field are computed using Lighthill acoustic analogy. The r.m.s. acoustic sources are highest near the trailing edge of the bump where the r.m.s. of wall pressure fluctuations has maximum value. The maximum correlation coefficient between $p_w$ and S occurs directly above the locations of maximum wall pressure fluctuations. The effect of the quadrupole source on the far-field acoustic density fluctuations is smaller thatn that of the dipole source at a low Mach number. The contribution of the lift dipole is dominant for the total acoustic field for all cases. The contribution of the volume quadrupoles to the total acoustic field gradually increases with the radius of the surface curvature δ/R.
