Experimental Analysis of Rotor Noise and Interference Effects in a Dual-Rotor Configuration

Urban air mobility (UAM) and parcel logistics increasingly rely on electrically powered unmanned aerial vehicles (UAVs), for which rotor-generated noise and propulsion efficiency represent key design challenges. This work presents an experimental investigation of single- and dual-rotor configurations conducted within the Hybrid Rotor Noise Optimization (HyRoNO) project. Aerodynamic and acoustic measurements were performed in a low-noise wind tunnel using a 168-microphone array, enabling detailed beamforming analyses for both the isolated and co-rotating configurations in hover. The acoustic measurements reveal that the interaction region between the lifting arm and the rotor remains largely independent of rotational speed (RPM) variations in specific frequency bands, allowing a distinct interaction zone to be consistently identified even as RPM increases. To assess rotor–rotor interaction phenomena, the spacing between the propeller axes was varied. The measurements demonstrate that, although dual-rotor operation introduces measurable acoustic interaction effects, the impact on thrust and power is minimal. Changes in rotor spacing influence both tonal and broadband components, while the interaction signatures themselves exhibit a strong dependence on frequency and geometric configuration. Moreover, modifications to the propeller design were shown to alter not only the aerodynamic loading but also the distribution and character of the dominant noise sources. These findings highlight the sensitivity of multi-rotor systems to both geometric adjustments and operational conditions, offering guidance for future low-noise rotor design.