Aeroacoustic Performance of Rotors in Tandem Configuration

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.