eVTOL Rotor Noise in Ground Effect

This study examines a hovering three-bladed two-rotor system in close operation to the ground. The rotor pair is oppositely phased and is examined for two heights, H/D = 1 and H/D = 0.5. Loads for these rotors are generated using the CFD solver AcuSolve, as well as the Rensselaer Multicopter Analysis Code (RMAC). The loads generated using CFD include aerodynamic interactions from inter-rotor effects and ground-rotor effects. These loads are coupled to the acoustic propagation PSU-WOPWOP code for acoustic predictions at an observer grid located at “ear height” from the ground. Rotors are also added below the ground to simulate perfect acoustic ground reflections. From the simulation results, the noise signals from the rotors were found to have a distinct directivity pattern of six locations of high noise and six locations of low noise caused by the rotor phasing. The introduction of aerodynamic interactions increases loading noise and has a significant effect on the high frequency noise content. These effects are amplified for the H/D = 0.5 case as the interactions are stronger. Ground reflections increased noise across the observer grid, and further enhanced the high frequency noise generated by the interactional aerodynamic loads.