Numerical study on noise reduction for eVTOL aircraft based on phase synchronisation method

With the rapid development of electric vertical take-off and landing (eVTOL) aircraft for urban air mobility (UAM), rotor noise has become a major barrier to their large-scale deployment. To reduce the cruise noise of tiltrotor eVTOL aircraft, this study develops a medium-to high-fidelity multi-rotor aeroacoustic prediction framework by coupling the reformulated vortex particle method (rVPM) with the Ffowcs Williams–Hawkings (FW–H) acoustic analogy. Based on this framework, phase-synchronisation analyses are first conducted for a tandem twin-rotor system to investigate the effects of relative rotor phase on far-field noise radiation. The aeroacoustic model is then integrated with a self-adaptive constrained Bayesian optimisation algorithm to minimise the average sound pressure level at the blade passing frequency (BPF) evaluated at seven observer locations. The optimised phase configuration reduces the target BPF sound pressure level by approximately 31.3 dB and decreases the overall sound pressure level at the point directly beneath the aircraft by about 7 dB. The analysis of the noise-reduction mechanism indicates that rotor phase adjustment can mitigate the wake-induced loading fluctuations of the rear rotors while promoting destructive acoustic interference among different rotors at far-field observation points. The proposed method causes no appreciable loss in rotor propulsive efficiency and provides a promising approach for low-noise rotor phase design in multi-rotor eVTOL aircraft.