Multifidelity Aeroacoustic Analysis of Quadrotor Biplane Tailsitter in Transition Flight

Abstract

The rapid emergence of urban and regional air mobility has intensified the need for accurate prediction of the aerodynamic and acoustic behavior of novel eVTOL aircraft operating in maneuvering flight regimes. Despite recent advances, significant gaps remain in the understanding of aeroacoustic phenomena during transitional maneuvers involving strong component interactions. This work addresses these gaps through a detailed aeroacoustic investigation of an 80-lb quadrotor biplane tailsitter aircraft undergoing a climb-to-cruise transition. A realistic climb-to-cruise maneuver was developed using a nonlinear dynamic inversion flight-dynamics framework. The flight-dynamics model was tuned using mid-fidelity solver DUST, and then prescribed to our in-house, high-fidelity CFD framework, Mercury. The resulting 3.2-s transition trajectory and control history were evaluated using time-accurate simulations and compared against a reduced-cost quasi-steady methodology. High-fidelity rotor loads showed good agreement with the prescribed vehicle motion, while airframe load predictions highlighted the importance of further tuning the flight-dynamics model. Quasi-steady analysis was shown to reliably capture mean aircraft loads and broadband noise levels, with good but more limited agreement for unsteady loading and tonal noise predictions. Installation effects were found to play a critical role throughout the transition, particularly during low-speed, high-thrust conditions. In particular the isolated rotor system experienced strong rotor-rotor interactions in the absence of the airframe. Discrepancies between quasi-steady and time-accurate results increased during periods characterized by strong aerodynamic interactions and flow disturbances. Acoustically, tonal noise dominated the early portion of the maneuver, while broadband rotor noise became more influential later in the transition. A-weighted noise levels were initially driven by higher-frequency airframe tonal contributions before transitioning to rotor broadband dominance. Overall, the results demonstrate an efficient methodology for AAM transition flight high-fidelity aeroacoustic analysis. Quasi-steady analysis was found to be an efficient and reliable tool for predicting AAM aeroacoustic behavior during transitional flight, although more limited success was achieved predicting aircraft loads and tonal noise directivity during strong component interactions. This work establishes a foundation for future high-fidelity maneuver-based aeroacoustic analyses.