UC Davis

This study examines the effects of ground proximity on the performance, aerodynamics, and aeroacoustics of NASA's side-by-side urban air mobility reference vehicle rotors in hover, utilizing high-fidelity computational fluid dynamics and aeroacoustic simulations. Two rotor overlap configurations (0% and 25%) at two different heights above the ground plane are evaluated. Results indicate that the ground plane significantly influences rotor performance, with the figure of merit improving as the rotor-ground distance decreases. The 0% overlap configuration shows increased blade sectional thrust, pressure fluctuations, and noise levels compared to the 25% overlap configuration, primarily due to reduced induced velocity; without rotor overlap, upwash flow more easily reaches the rotor disk plane. Aerodynamic interactions intensify with proximity to the ground, particularly as rotor-ground distance decreases. Notably, the 25% overlap configuration provides a noise reduction of 3-4 dBA near the ground compared to the 0% overlap setup. However, despite its noise reduction benefit, the 25% overlap configuration poses greater safety concerns close to the ground, as indicated by an elevated hazardousness factor relative to the 0% overlap configuration. Finally, noise directivity exhibits substantial differences between A-weighted and unweighted overall sound pressure levels, with A-weighting mitigating acoustic interference effects