Analyses on aeroacoustic characteristics of coaxial rotors in hover

A numerical method which combined CFD (Computational fluid dynamics) method and FW-H (Ffowcs Williams-Hawkings) equations is established to simulate the acoustic characteristics of the coaxial rigid rotor in hover. In order to simulate the vortex interaction and unsteady characteristics accurately, based on the moving-embedded grid technology and a dual-time method, the simulation method is developed by solving the compressible Reynolds-averaged Navier-Stokes (RANS) equations with Baldwin-Lomax turbulence model. The acoustic characteristics of the coaxial rotor can be predicted by formulation Farassat 1A, and the motion law and aerodynamic loads of sound sources can be obtained from blade surface girds directly. Then, the sound pressure time history and noise spectrum characteristics on the thickness, loading and total noise of the coaxial rotor have been analyzed in detail. The simulated results demonstrate that the feature that two axially aligned rotors rotate in opposite directions has significant effects on the sound pressure wave, and the phases of peak value in different observation direction show differences and some phenomenon such as Venturi effect, blade-vortex interaction, downwash effect make the blade loads show obvious unsteady characteristics, which cause the strong loading noise radiation The total noise is widely dominated by thickness noise in the low frequency band and by loading noise in the high frequency band.