Effect of Initial Phase Difference on Aerodynamics and Acoustics of a Coaxial Counter-Rotating Rotor

Urban air mobility (UAM) is promising as next-generation transportation systems, but noise pollution remains a major obstacle for its widespread use in densely populated urban areas. The complex configuration of UAM vehicles utilizing distributed electrical propulsion (DEP) systems leads to strong interactions between multiple rotors and adjacent structures, such as airframe, pod, pairing, and fuselage. Interactional aerodynamic phenomena are the dominant noise source in UAM aircraft. This study focuses on investigating the interaction effects on both aerodynamics and noise generation of coaxial counter-rotating rotor using the lattice-Boltzmann method (LBM). The simulation results showed that the existence of airframe results in an increase in overall sound pressure level (OASPL), compared to the isolated rotor configuration. Moreover, a novel noise reduction technique for coaxial counter-rotating rotors with the airframe is proposed, involving the control of the initial phase difference between the upper and lower rotors. This technique is suggested to reduce the noise levels effectively by alleviating the vibration loads acting on both the rotors and the airframe.