LAUSR

Abstract This study presents measurements of the far-field noise radiated by forward-facing steps with and without rounded corners. A noise prediction formula, obtained by combining theory and measurements, to predict noise radiated by an unrounded forward step is also presented. The prediction methodology has also been extended to include the effects of rounding the step corner. The height of the step in measurements ranged between 78% to 84% of the incoming, turbulent wall-jet boundary layer. The Reynolds number based on step height was between 8300 and 16,800. Six roundings of the step corner were considered with radii equal to 0%, 6.25%, 12.5%, 25%, 50%, and 100% of the step height. It was found that rounding the forward step corner reduces the noise without affecting its directivity and scaling significantly. A slight rounding of the corner only affects the noise at high frequencies, however, a further increase in rounding leads to a broadband noise reduction. The prediction formula for the unrounded forward step yields reasonably good agreement with both past and present measurements. The predictions also suggest that the noise generated by a forward step is independent of the incoming boundary-layer thickness and scales with the step height. The predictions for rounded forward steps show that the noise attenuation due to corner rounding can be reasonably approximated if it is assumed that the unsteady surface loading in the vicinity of rounded steps scales with the reattachment length associated with each rounding.