The experiment on phase coherence active noise control of dual-rotor

With the rapid development of the low-altitude economy, noise emissions from multirotor aircraft have become an increasingly prominent issue. Theoretical studies have indicated that phase-coherent active noise reduction represents a novel approach for reducing the acoustic signature of multirotor aircraft. In this study, an experimental investigation was conducted to examine the effects of phase-angle difference, inter-rotor spacing, and their combined configurations on the noise characteristics of a dual-rotor system. Far-field microphones were used to measure the acoustic responses under different operating conditions. The results show that the directivity pattern of the 1BPF noise of the dual-rotor system exhibits a four-lobed structure. As the phase-angle difference increases, the lobes rotate counterclockwise in the polar directivity map, indicating that the phase-angle difference can regulate the spatial radiation direction of the tonal noise generated by the dual rotors. Different phase-angle differences produce significant noise control effects at specific observation points. The active noise reduction strategy substantially decreases the tonal noise of the dual-rotor system, with a maximum reduction of 10.27 dB in the 1BPF noise and 2.95 dB in the overall sound pressure level (OASPL). The influence of inter-rotor spacing on phase-coherent active noise reduction was further investigated. The results demonstrate that when the inter-rotor spacing is reduced to 2.2R and the phase-angle difference is set to 45°, the 1BPF noise can be reduced by 10.7 dB, while the OASPL can be reduced by 2.37 dB. Therefore, rational design of the phase-angle difference and inter-rotor spacing can effectively reduce the noise level at prescribed observation points. This study experimentally validates the feasibility of phase-coherent active noise reduction for dual-rotor systems and reveals the effects of phase-angle difference and its coupling with inter-rotor spacing on noise directivity and noise reduction performance. The findings provide experimental evidence for the low-noise layout design of multirotor aircraft.