An experimental study was conducted to investigate the effect of the bevel angle on the radiated noise and the associated flow-field over the trailing-edge. The bevel angle of the trailing-edge was adjusted over a broad range of angles to demonstrate the aeroacoustic properties of the attached and separated boundary layers. The far-field noise results obtained from the beamforming array were assessed in conjunction with the associated flow-field. Far-field measurement results show an increased level of radiated noise for a range of bevel angles where the flow remains attached compared to the baseline flat-plate case without a bevel angle. Near-field measurements are presented in terms of pressure coefficients, unsteady surface pressure results, turbulence properties of the boundary layer, and corresponding spectral properties of these quantities. The near-field measurement results indicate that introducing a bevel angle yields a region of favorable pressure gradient on the flat-plate and bevel, which accelerates the flow and reduces the size of structures in the boundary layer up until the mid-bevel region, which then decelerates toward the trailing-edge. This change increases the energy content of surface pressure fluctuations as well as the energy content of the velocity field over the trailing-edge and wake, which, in turn, results in an increased radiated far-field noise as supported by beamforming results. Furthermore, at a sufficiently high bevel angle, where pronounced flow separation occurs, the lack of interaction between trailing-edge and shear layer leads to a significant reduction in the radiated far-field noise compared to that of the baseline flat-plate.
This experimental study presented in this paper aims at understanding the complex aeroacoustics relationship between small-scale rotors in tandem configurations. The effect of the upstream rotor on the aeroacoustics of the multi-rotor system in a counter-rotating configuration was studied. Two rotors in tandem alignment were tested for varying separation distances, free-stream velocities, and tilt angles for the upstream rotor. The results are presented in terms of power spectral density of the acoustic pressures and the directivity of the overall sound pressure levels. The results show that the presence and position of an upstream rotor significantly affect the rotor system's noise signature. The tip-to-tip separation distance affects the magnitude of the radiated noise at the first blade passing frequency. Additionally, an increase in the free-stream velocity increases the radiated broadband noise. The OASPL directivity patterns show a minimal sensitivity to the free-stream velocity except for a few exceptional cases. Finally, the tilt angle of the upstream rotor has a significant effect on the OASPL directivity at higher tilt angles.
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