Multi-fidelity aeroacoustic prediction of an eVTOL rotor

The rising interest in urban air mobility has brought new challenges in terms of noise pollution. Developing dedicated methods to accurately predict the noise generated by such aircraft configurations is thus a cornerstone to be able to meet the noise emission requirements in an urban environment. This work presents three numerical approaches, with different levels of fidelity, which aim at predicting the noise produced by such configuration: a lifting-line code with free wake, an innovative intermediate approach based on a Reynolds-averaged Navier–Stokes/Blade Element Theory (RANS/BET) coupling, and an Unsteady Reynolds-Averaged Navier–Stokes (URANS) approach. These methods are assessed on a rotor representative of those installed on an electric Vertical Take-Off and Landing (eVTOL) aircraft. A thorough comparison of the aerodynamic features and the noise predicted by each approach is presented for two challenging operating conditions, namely hover and edgewise flight. Their capacity to account for the effect of a supporting arm is also assessed. Only the URANS method is able to accurately predict the blade-vortex interactions that characterize both operating conditions as well as installation effects due to the supporting arm. The RANS/BET method has limitation in the capture of blade-vortex interaction while the lifting-line approach fails to predict accurately the installation effect. Nevertheless, those two proposed alternative approaches allow to significantly reduce the CPU and manpower costs inherent to the use of a URANS simulation with discrepancies in terms of mean and maximum levels lower than 3 dB in all the considered configurations.