Investigation of Unsteady Pressure Fluctuations in Flow over Backward-Facing Step

Abstract

Flow over a backward-facing step at , based on the step height, is simulated using the Divergence Free Synthetic Eddy Method of Poletto et al. (“A New Divergence Free Synthetic Eddy Method for the Reproduction of Inlet Flow Conditions for LES,” Flow, Turbulence and Combustion, Vol. 91, No. 3, 2013, pp. 519–539.), implemented in OpenFOAM® 1606, which preserves the instantaneous fluctuating pressure field in the domain, which is normally lost. Examination of the pressure spectra at various positions normal to the wall is well represented by wall-pressure measurements at all but the highest frequencies examined here. Various spectral peaks corresponding to shear-layer movement, discrete vortex shedding from the step, and numerous shear-layer instabilities are investigated using power and cross-spectral measurements of the fluctuating wall pressures. Convective velocities obtained from the cross-spectral phase indicate that the lowest frequencies convect slowly, whereas the higher frequencies near the measured spectral peaks convect at . There is an increase in convective velocity as the measurement locations are moved farther downstream. Additionally, an increase in peak frequency was found in this examination; however, the increase in convective velocity (approximately equal to 33%) and frequency (approximately equal to 7–11%) calculated at different streamwise positions were not found to be directly proportional, indicating that the increase in peak frequency cannot be solely explained by flow acceleration but that the structures are likely undergoing streamwise or spanwise deformation as well.