Assessment and mitigation of the rotor noise for future urban air mobility vehicles

Abstract

Multi-rotor configurations are often adopted in urban air mobility (UAM) designs. The aerodynamic noise of rotors is a significant source of the UAM vehicles, requiring systematic measurements and mitigation. To this end, a large-scale test rig is designed and built to enable the acoustic measurement of UAM rotor blades. The test rig is placed in an anechoic chamber with the size of 8.1 m (L) × 6 m (W) × 5.1 m (H). The aerodynamic force and noise of a pair of custom-designed blades with a radius of 0.5 m are measured. The rotational speed ranges from 600 to 1800 revolutions per minute. A zig-zag turbulator is applied on the blade surface to trip the boundary layer. The effect of the turbulator on rotor noise is negligible compared to the untreated case, indicating that the blade boundary layer is fully developed. Particulate roughness is then implemented on the blade surface to explore the potential of noise reduction for turbulent blade boundary layers. Results show that a reduction of 3 dB in high-frequency broadband noise can be achieved upstream and downstream of the rotor at 1800 RPM when the particulate roughness is applied on the leading-edge region of the blades.