Wall-pressure fluctuations in a high-Reynolds-number turbulent-boundary-layer flow over a forward step*

Large-eddy simulations are performed to investigate the turbulent boundary-layer flow over a small forward-facing step at momentum-thickness Reynolds number of 15,500 and step-height Reynolds number of 26,600, with a focus on the effect of the step on wall-pressure fluctuations.  The step height is 15% of the unperturbed boundary-layer thickness.  Both wall-modeled LES and wall-resolved LES are employed, and consistent results are obtained for the spatiotemporal characteristics of the fluctuating wall pressure.  The LES predicts step-elevated wall-pressure frequency spectra comparable to those from earlier experimental and numerical studies at the same step-height Reynolds number and lower momentum-thickness Reynolds numbers, but underpredicts the low-frequency spectral level relative to the measurements at Virginia Tech (Awasthi et al., J. Fluid Mech. Vol. 756, 2014) that match both Reynolds numbers.  Two-point and space-time correlations are predicted well compared with the experimental data.  They show a significant decrease in correlation length and time scales at the high Reynolds number in the unperturbed boundary layer, and a drastic increase in correlation scales after the step due to step-induced disturbances, which decay slowly in the downstream.  The fluid dynamic sources of the wall-pressure fluctuations and their downstream evolution will be discussed.