Interactional Aerodynamics and Aeroacoustics of Helicopter Main-Rotor/Tail-Rotor and Main-Rotor/Fuselage

Abstract

This paper address two problems of the helicopter flowfield: the aerodynamic and aeroacoustic interaction between a) the main- and the tail rotor and, b) between the main rotor and the fuselage. The first interaction is analyzed with a numerical approach; the main rotor/fuselage interaction study, restricted to aerodynamics, is based on wind tunnel experiments. The rotor interactions studied are for a) a two-blade main- and tail rotor in hover, and b) a four-blade main- and a two-blade tail rotor in climb flight. Parameters varied for the hover configuration are the lateral spacing between the main- and tail rotor and the sense of tail rotor rotation. The unsteady pressure on the main- and tail rotor blade surface is calculated with a 3-D unsteady free wake panel method and used as input to a Ffowcs Williams Hawkings-equation based code to evaluate the aeroacoustics. Main rotor effects a significant change in the noise directivity pattern and noise level of the tail rotor. Tail rotor contribution to the total noise dominated during the climb flight. Main rotor/fuselage aerodynamic interaction is analysed from pressure and flow visualization data of wind tunnel tests. Test parameters are rotor thrust and advance ratio. Rotor downwash and fuselage flow vary with flight condition and govern the flow aerodynamics. The global flowfield is strongly dependent on the rotor thrust and advance ratio.