| The thermal components and exhaust plume of helicopter engine exhaust system are the main tracking targets for the infrared detection and guidance.Infrared suppressor is an effective way to reduce infrared radiation.The lobed mixer-ejector infrared suppressor is an advanced configuration,which uses kinetic energy of engine exhaust to pump and mix the ambient air,mainly against the infrared detection in the 3~5?m band.In order to improve its performance further,the effect of lobe configuration on the pumping ability of the short lobed mixer-ejector and the effect of louvers on the cooling of the mixed duct are investigated in the current study.This paper mainly includes the following research contents:Firstly,the experimental study on the wall cooling of scaled IR suppressor test model is carried out.The effects of different mass flow rates of cooling air flow and different aspect ratios of louver on the wall cooling performance are analyzed.The results show that with the increase of the mass flow rate of the cooling air,the temperature of the mixing duct decreases at all three louver aspect ratios.Along the flow direction,the temperature gradually increases with the increase of the louver aspect ratio,and the temperature is the lowest when the louver aspect ratio is 2.Along the circumferential direction,the temperature decreases with the increase of the louver aspect ratio,and the temperature is the highest when the louver aspect ratio is 2.As the louver aspect ratio increases,the incidence angle of the cooling airflow decreases when the cooling airflow enters the mixing tube,the penetration of the cooling air into the mainstream increases,the effect of the film corverage is weakened,which is unfavorable to the spreading of the cooling airflow along the flow direction but favorable for cooling air flow spreads in the width of the louver.Then,the flow field of lobed mixer-ejector is numerically analyzed.The relationship between the flow separation and the lobe angle and the influence of the lobe trailing scarfing on the pumping perormance and the total pressure recovery coefficient are illustrated.The results show that when the lobe angle is 50°,the phenomenon of flow separation inside the lobed mixer-ejector is obvious.For the lobed mixers with lobe angles of 40° and 45°,both the pumping coefficient and the total pressure recovery coefficient are increased with the increase of the lobe trailing scarfing angle.For the lobed mixer with lobed angle of 50°,both the pumping coefficient and the total pressure recovery coefficient tend to increase firstly and then decrease with the increase of the lobe trailing scarfing angle.For the short lobed mixer,no matter how big the lobe angle is,by the lobe trailing scarfing treatment,the pumping coefficient and the total pressure recovery coefficient all increase compared with the original mixer.Finally,in view of the structural ferature of the lober mixer-ejector,the cooling structure by using louvers on the curved duct is proposed,and the infrared characteristics are numerically studied.The results show that:(1)for the single row of louvers,with the increase of mass flow rate of cooling air,both the gas and the total infrared radiation intensity in all detection angles are decreased gradually,expecially for the total infared radiation intensity.When the louvers are located at the bottom of the mixing duct,the infrared radiation intensity either in the horizontal or vertical direction is the lowest.The situation for the louvers on the outside of the mixing duct in next,and the situation for the louvers on the inside of the mixing duct is the highest.Under the same mass flow of cooling air,the infrared radiation intensity of the suppressor is the lowest when the shielding distance(p)is 50 mm.(2)For the multiple-row of louvers,the total infrared radiation intensity of the infrared suppressor is the lowest when the arrangement of louver is 7×4.Under a smaller usage of the cooling air mass flow,with the increase of the louver height(s),the infrared radiation intensity in the horizontal direction increases first and then decreases,and the radiation intensity in the vertical direction is the most non-uniform and then decreases gradually when s=10 mm.When the cooling mass flow is 0.0984kg/s,the infrared radiation intensity is lower when the louver height is 20 mm.The total infrared radiation intensity of the infrared suppressor is the lowest when the louver aspect ratio is 18. |
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