Comparative Analysis of Direct Method and Fast Multipole Method for Multirotor Wake Dynamics

The rapid growth of urban air mobility (UAM) and electric vertical take-off and landing (eVTOL) aircraft has spurred the demand for designing efficient next-generation urban transport. Distributed electric propulsion (DEP) systems, employing multiple lifting rotors or prop-rotors, offer promising solutions for eVTOL aircraft. However, accurately simulating the complex wake flow resulting from rotor interactions poses significant computational challenges. This study aims to compare the feasibility and effectiveness of the direct method and fast multipole method (FMM) in predicting wake geometry and vortical structures. Vortex particle method (VPM) simulations utilizing both methods are conducted on various rotor models, analyzing key parameters such as tip vortex trajectory, wake geometry, vortical structures, and wake-induced downwash. The findings highlight the effectiveness of FMM in accurately capturing the intricate wake flow of isolated- and multirotor systems by comparing the computational times. This study contributes to the comprehensive understanding of wake dynamics and rotor aerodynamics, providing valuable insights for design engineers. In addition, simulations of multirotor systems in hover and forward flight conditions demonstrate the feasibility of employing VPM with FMM in realistic operational conditions.