The effect of step rounding on the noise generated by flow over small forward-facing steps in a low-Mach-number turbulent boundary layer is studied using large-eddy simulation and Lighthill's theory. The step height is 26% of the thickness of the unperturbed turbulent boundary layer at Ree = 4755, and the rounding radius relative to the step height ranges from 0 to 100%. Step rounding is shown to cause reduced flow separation on the upper surface and increased level of peak pressure fluctuations. The downstream relaxation to equilibrium turbulent boundary layer is faster for steps with larger rounding. The sound spectral level is significantly reduced by step rounding, mainly due to reduced surface diffraction effect. The noise reduction increases with increasing rounding radius and frequency. The effect of step rounding on acoustic directivity is insignificant for acoustically compact steps, but grows with increasing acoustic non-compactness of the step height.
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