Sound Radiation from Rounded Steps and Gaps

Abstract

Experiments have been performed to document the aeroacoustic behavior of rounded step and gap configurations embedded in a wall jet boundary layer at low Mach number. Measurements include far-field sound and surface pressure fluctuations. Rounding is found to substantially reduce the sound produced by a forward step. Sound levels drop by between 3 and 7dB per doubling of the corner radius for radii greater than 6.25% of the step height. Directivity in the sound field is affected by the acoustic non-compactness of the step but appears consistent with previous modeling efforts. Noise from a gap formed by a backstep and forward step of the same height is dominated by sound radiated from the forward step component and has similar directivity to the forward step. Rounding of the upstream edge of the gap has no influence on its sound field, independent of gap. Rounding of the downstream edge attenuates the sound produced, much as it does for the forward step