Effects of forward-flight speed on plume flow and infrared radiation of IRS-integrating helicopter

To address deeper understandings about the aero-thermal performance of an integrating infrared suppressor under more realistic situations,a numerical investigation is motivated in the current study,concerning the effects of forward-flight speed on exhaust plume flow and infrared radiation of the Infrared Suppressor-integrating(IRS-integrating)helicopter,wherein the forward-flight speed is changed from 0 m/s(hover state)to 100 m/s,while both the engine exhaust parameters and the main-rotor operation parameters remains unchanged during different forward-flight velocities.The results show that the interaction between forward-flight flow and downwash flow alters the exhaust plume development and the internal flow inside the IRS-integrating rear fuselage more complicatedly,tightly dependent on the forward-flight speed.Of particular concern is the situation where the forward-flight flow has nearly the same level as the downwash flow,the hot mixing flow could possibly interacts with the helicopter rear fuselage to play a local heating effect.With the increase of forward-flight speed,the ejection coefficient is generally increased and the average exhaust temperature of mixing flow is decreased,leading to a reduction of the infrared radiation intensity of exhaust plume in 3–5 lm band.However,the influence of forward-flight speed on the overall infrared radiation intensity of IRS-integrating helicopter is conjectured not monotonous due to the complicated interaction between forward-flight flow and downwash flow.Under high-speed forward-flight states,the overall infrared radiation intensity of the IRS-integrating helicopter in 3–5 lm band is reduced with the increase of forward-flight speed.With respect to 3–5 lm band,the forward-flight speed has little effect on the infrared radiation in 8–14 lm band.