Acoustic Predictions for Side-by-Side Rotor with Ground Effect

Abstract

Influence of the ground plane on the performance, aerodynamics, and aeroacoustics of NASA's side-by-side Urban Air Mobility (UAM) reference vehicle rotors in hover is investigated using high-fidelity computational fluid dynamics (CFD) and aeroacoustics simulations. CFD simulations are carried out with Helios, while acoustics calculations are conducted using PSU-WOPWOP. Two overlap cases, each at two different rotor heights, are considered. The results demonstrate a significant influence of the ground plane on rotor performance, with the figure of merit (FM) increasing as the distance between the rotors and the ground is reduced. The 0% overlap configuration shows an increase in blade sectional thrust, pressure fluctuations, and resulting noise levels compared to the 25% overlap configuration, primarily due to lower induced velocity as a result of having no rotor overlap, allowing upwash to reach the rotor disk plane. Aerodynamic interactions intensify with the presence of the ground plane and become more pronounced as the rotor-ground distance decreases. The 25% overlap configuration is found to provide a noise reduction benefit of 3-4 dBA near the ground compared to the 0∖% overlap configuration. Furthermore, a considerable difference is observed in the noise directivity between A-weighted and unweighted OASPL. A-weighting notably reduces regions of acoustic interference.