Numerical Study of the Main Rotor Wake Structures and Induced Velocity Fields at the Tail Rotor Location When Flying Near the Ground

This paper considers the Mi-8 helicopter main rotor aerodynamics when flying near the infinite ground surface. The research is based on the free wake model developed by authors at Moscow Aviation Institute. The distance from the rotor's hub to the ground surface in the range of H = 6−16 m and the values of free stream (flight) velocity in the range of V = 0−15 m/s are considered. The results of the visualization for both rotor wake shapes and streamlines are obtained. The influence of the ground proximity on the rotor wake shape, including the formation of "supervortex" and "ground vortex" structures are analyzed. The induced velocity fields of the main rotor in the area of the tail rotor location for various azimuth positions relative to the main rotor axis are studied. The conclusion is made about the significant influence of the ground effect on the rotor wake structure and induced velocities field, including the area of the tail rotor location. Particularly, at slip flight with speed V = 10 m/s, when the distance to the ground surface H increases from 6 to 12 m, the value of the average induced velocity at the tail rotor plane is growing up to four times. The obtained data have allowed taking into account such effects of aerodynamic interference in the simplified mathematical model of the research flight simulator of JSC Helicopters Mil and Kamov.