Aerodynamics and aeroacoustics of helicopter main-rotor/tail-rotor interaction

Abstract

Preliminary results from an ongoing effort to model the interaction aerodynamics and aeroacoustics of main- and tail rotor of a helicopter in subsonic flow are presented. The configurations studied are 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. The numerical approach consists of computing the unsteady pressure on the main- and tail rotor blade surface with a 3-D unsteady free wake panel method and using this as input to a Ffowcs Williams Hawkings equation based aeroacoustic code to evaluate the noise characteristics. Parameters varied for the hover configuration are the lateral spacing between the main- and tail rotor axis and the sense of tail rotor rotation. Main rotor interaction effects a significant change in the noise directivity pattern and noise level of the tail rotor. Tail rotor contribution to the total noise dominates during the climb flight.