Effects of rotor downwash on exhaust plume flow and helicopter infrared signature

The effects of rotor downwash and exhaust direction on plume flow field, rear-fuselage temperature distribution and helicopter infrared signature were numerically investigated. The internal flow inside IR suppressor originated from engine exhaust nozzle and the external flow around helicopter airframe originated from rotor downwash were computed in a coupled mode to determine the temperature distributions on the helicopter skin and in the exhaust plume. Based on the skin and plume temperature distributions, a forward–backward ray-tracing method was used to calculate the infrared radiation intensity from the helicopter with a narrow-band model. The results show that the exhaust plume takes on strong downwards deflection to the rear-fuselage, as well as to the rotor rotational direction under the action of rotor downwash. The rotor downwash has a complicated influence on the infrared radiation distribution of helicopter. It is benefit for reducing the infrared radiation intensity when the exhaust is ejected in oblique-turned or lateral-turned mode. While for the up-turned exhaust mode, the exhaust plume could heating the helicopter rear-fuselage and the infrared radiation intensity may be enhanced under the action of downwash.