Numerical Characterization of the In-Flight Noise Footprint for a Reference Multirotor Vectored-Thrust eVTOL

Abstract

This work presents a high-fidelity aeroacoustic investigation of a distributed-propulsion eVTOL aircraft during representative urban air mobility departure operations. Three flight conditions are analyzed, namely vertical take-off, transition, and cruise in climb. The aerodynamic analysis highlights substantial differences in wake development and rotor–rotor interactions among the investigated configurations. For the particular vehicle configuration, cruise conditions are characterized by the ingestion of coherent wake structures by the tail-mounted propellers, resulting in significant unsteady loading fluctuations. The aeroacoustic analysis, performed using the permeable and solid formulations of the Ffowcs Williams–Hawkings integral equation, shows that the radiated noise is dominated by tonal components, with cruise conditions exhibiting blade passing frequency levels approximately 10 dB higher than the other configurations. Source identification analyses indicate that the dominant acoustic contribution is associated with the unsteady loading noise generated by the tail-mounted propellers due to wake ingestion. Finally, an on-ground footprint analysis based on a complete reference departure trajectory demonstrates compliance with current EASA certification limits, while also highlighting the strong sensitivity of the acoustic footprint to the transition maneuver. The results highlight the importance of rotor wake interactions in cruise conditions for short-aspect- ratio distributed-propulsion eVTOL configurations, where wake ingestion by downstream propellers significantly increases tonal noise levels and directly affects the resulting certification footprint. These findings emphasize the need to account for rotor interaction effects during both preliminary design and acoustic certification assessment.