The exhaust plume flow characteristics subjecting to the action of helicopter rotor downwash air flow were investigated based on CFD numerical calculations.And the effects of rotor downwash air flow velocity and exhaust direction on the exhaust plume flow and pumping capacity of the exhaust system were analyzed.Results show that:exhaust plume yields flow strong downward deflection to the rear fuselage

as well as deflection to the rotor rotational direction;under the action of rotor downwash air flow

these deflections are especially obvious under higher rotor downwash air flow;when the exhaust is ejected upwards

the exhaust plume flow could come into collision with rear fuselage; pumping capacity of the exhaust system is weakened slightly and pumping coefficient decreases approximately 0.01;while the exhaust is ejected obliquely or laterally

the exhaust plume flow do not come into collision with rear fuselage; pumping capacities of the exhaust system are somewhat enhanced and pumping coefficient increases maximally 0.12.