Aeroacoustics of Rounded Forward-Facing Steps: Near-Field Behavior

Measurements of wall pressure fluctuations induced by forward-facing steps with rounded corners immersed in a turbulent boundary layer were performed. Four different roundings of the step corner (r) equal to 0, 6.25, 12.5, and 25% of the step height (h) were considered. The step height was 26.2% of the undisturbed boundary-layer thickness, and the Reynolds number based on step height ranged between 35,000 and 104,000. The results show that both mean and fluctuating pressure upstream of the step remain independent of the corner rounding, whereas they are a strong function of rounding on the downstream surface. The latter was found to be due to a reduction in the spatial extent of the separation bubble with increasing rounding. The fluctuating pressure on the vertical face of the steps was found to increase with increasing corner rounding. For r/h <= 12.5%, the pressure spectra within the downstream separation bubble, and sufficiently away from the salient corner, were found to scale on the reattachment length and free-stream velocity. Downstream of the separation bubble, the spectra evolve differently and a separate scaling, one which suggests that the pressure fluctuations evolve independently of the incoming boundary layer, is shown to collapse the spectra.