Facing the challenge of eVTOL noise prediction with low-order methods

Abstract

Urban Air Mobility (UAM) vehicles will operate close to populated areas, where noise mitigation is a key design driver. Their distributed propulsion architecture produces complex aerodynamic interactions that shape distinct acoustic signatures. These are dominated by tonal components, originating from periodic unsteady loading caused by rotor–rotor and wake–rotor interactions. Capturing such mechanisms efficiently is essential for noise-aware design and optimization. This study evaluates the Vortex Particle Method (VPM), implemented in FLOWUnsteady, as a mid-fidelity approach for predicting and understanding these tonal noise mechanisms in the early design phase. The method resolves unsteady vortex dynamics without meshing and is benchmarked against Blade Element Momentum Theory (BEMT), Lattice Boltzmann (LBM), and unsteady RANS simulations for three operating conditions: hover, climb, and cruise. Results show that VPM accurately reproduces aerodynamic loading trends and tonal noise signatures in unsteady regimes, particularly for hover and climb, while convergence time and sensitivity to particle resolution remain limiting factors. For steady cruise conditions, VPM performance aligns closely with BEMT predictions. Overall, VPM demonstrates strong potential to bridge the gap between low-order efficiency and high-fidelity accuracy, providing physically consistent tonal noise trends for UAM rotor predesign and optimization.