A computational aeroacoustic study of a multi-rotor powered urban air mobility vehicle

Abstract

The multi-rotor propulsion system has become one of the popular configurations for urban air mobility vehicles due to its capability of high-density vertical take-off and landing operations. The noise characteristics, as a critical criterion for urban air mobility, usually differ for a multi-rotor configuration from a single-rotor configuration. In this work, we investigate the noise generated by a hexacopter configuration using delayed detached eddy simulations and the Ffowcs-Williams and Hawkings acoustic-analogy-based solver. The overall length and the rotor diameter of the vehicle are 4 m and 2 m, respectively, and the target maximum take-off mass is 500 kg. The full configuration and three simplified setups that reduce several individual components are numerically studied to isolate the corresponding effect of each component and to identify their flow/acoustic interactions. The results show that the rotor-rotor interaction leads to remarkable thrust fluctuations and further results in a considerable increase in tonal noise over a broad frequency range. The interaction between the rotors and the support arms also leads to significant thrust fluctuations on the surfaces of both rotor blades and arms, which produces additional tonal noise at high-order harmonics of the blade passing frequency. In contrast, for the current configuration, the existence of the fuselage does not have a significant effect on noise generation. The research should benefit low-noise vehicle design and operation.