Investigation of aerodynamics, wake dynamics, and aeroacoustic characteristics of a full-configuration tiltrotor aircraft during transition flight

Abstract

This study presents a numerical analysis of the aerodynamic and aeroacoustic behavior of a full-configuration tiltrotor aircraft during transition flight. This regime poses unique challenges due to the combined effects of varying nacelle tilt angles, rotor-fuselage aerodynamic interference, and complex unsteady wake interactions. Herein, the XV-15 tiltrotor configuration is analyzed using a coupled-vortex framework that incorporates a source-doublet panel method and time-accurate vortex particle method, enabling accurate predictions of unsteady aerodynamic loads and wake development. Rotor noise is evaluated using Farassat's Formulation 1A of the Ffowcs Williams-Hawkings equation, focusing on tonal noise radiation associated with unsteady blade loading. Results indicate that increasing the nacelle tilt angle results in stronger aerodynamic asymmetry, intensifying unsteady blade loads and generating highly distorted wake structures. The developed helical wake transitions into a more irregular, turbulent wake as the nacelles approach the helicopter mode, directly affecting rotor performance and noise radiation. Moreover, fuselage and wing substantially alter wake development, enhances wake interactions, and contributes to additional loading noise components. Aeroacoustic analysis revealed that the overall sound-pressure level increased by similar to 4 dB as the nacelle tilt angle varied from 15 degrees to 60 degrees, accompanied by a forward shift in dominant noise lobes. Notably, phase differences in sound pressure emitted from the rotor blades induce constructive and destructive interferences, depending on observer location. These findings contribute to advancing the understanding of transition flight aerodynamics and aeroacoustics, with implications for next-generation rotorcraft.