Aeroacoustic Analysis of a Lift-Offset Coaxial Rotor Using High-Fidelity CFD-CSD Loose Coupling Simulation

This paper presents the investigation of acoustics of a lift-offset coaxial rotor in high-speed steady forward flight using high-fidelity Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) loose coupling tools - Helios and RCAS. Acoustics of the lift-offset coaxial rotor is simulated using the acoustic prediction tool PSU-WOPWOP at eight chosen microphones positioned below the rotor plane. Three forward flight speeds at 100, 150, and 200 knots are selected to investigate the effect of lift-offset, flight speed, and separation distance on acoustics of the coaxial rotor. The total power of the three speed cases is validated against flight test data and shows good agreement. Strong blade-crossover interactions and self-BVI signatures of the coaxial rotor, which are sources of loading noise, have been captured in details via high-fidelity CFD simulations across all speed cases. It has been demonstrated that the magnitude of sound pressure level increases significantly with increasing flight speed and lift-offset. The strength of blade-vortex interaction sound pressure level (BVISPL) appears to decrease dramatically with increasing separation distance at 100 knots. However, higher speed cases do not show a significant reduction in BVISPL with increasing separation distance. Overall, this research study presents noteworthy and novel findings on acoustics of a lift-offset coaxial rotor.