Aeroacoustic Analysis of a Quadrotor Biplane Tailsitter in Climb and Synchrophased Hover

Unmanned Aerial Vehicles (UAVs) have seen a recent rise in popularity as a result of their vertical take-off and landing (VTOL) capabilities and their ability to perform a wide variety of missions. Despite large advancements in UAVs, their success in commercial operations remains hindered by high noise footprints. This brings forward a need to better understand the acoustic properties of these aircraft, and the aerodynamic interactions that cause them. In this study, a quadrotor biplane tailsitter trimmed in hover and in 3 m/s climb are compared. High-fidelity aerodynamic simulations are performed using University of Maryland's Reynolds-averaged Navier Stokes (RANS) equations-based computational fluid dynamics (CFD) framework, Mercury. Acoustic analysis is performed with ACUM, a Ffowcs Williams - Hawkings solver. Broadband noise is calculated using the Brooks, Pope, and Marcolini semi-empirical method. The climb trim was found to have 13 dBA reduction in peak noise on the ground when compared to baseline hover. Synchrophasing was then implemented as a noise reduction strategy on hover, the louder flight condition. A 90° phase angle between adjacent rotors saw a 10 dBA reduction in the ground plane peak noise.