Research On Some Problems Of Infrared Characteristics And Stealth Technology Of Aero-Engine Exhaust System

The objective of this thesis was to develop the infrared stealth technology of aero-engine exhaust system,a modified version design method of axisymmetric unmixed-flow exhaust system based on CFD numerical simulation was established to suppress the infrared radiation characteristics,and research on the flow field and infrared characteristics of a turboprop engine exhaust system.The main contents include the following aspects:(1)Numerical simulation on the aerodynamic and IR characteristics of axisymmetric unmixed-flow exhaust system of turbofan engine;(2)Reconstruction of the reference axis symmetrical separation exhaust system into S-2D mixed exhaust system and the flow matching was completed.(3)Studied the effects of mixer profile type and profile parameters on the aerodynamic and IR characteristics of the S-2D mixed exhaust system.(4)Researched the aerodynamic and IR characteristics of the turboprop exhaust system at different propeller speeds.The main research results include:(1)The axis-symmetric separation exhaust system is modified to low-infrared characteristic S-2D mixed exhaust system with the infrared stealth technology such as 2D nozzle and S-2D flow channel.Compared with the reference axis symmetrical separation exhaust system,the S-2D exhaust system has an infrared radiation intensity reduction of more than 44.6% in the omnidirectional detection angle,and the high-temperature components inside the exhaust system are obscured,and the maximum reduction is 93.1%;(2)Reachered the effects of mixer profile type and profile parameters on the aerodynamic and IR characteristics of S-2D mixed exhaust system.Results show that compared with splitter mixer,the thrust of the exhaust system with bending mixer is increased by 0.7%,but the infrared stealth characteristics is worse,and the longer of the bending mixer,the better of the infrared stealth characteristics of the exhaust system.Compared with splitter mixer,the thrust of the exhaust system with lobe mixer is reduced by 1.3%,and the infrared radiation intensity is significantly reduced in = 0~10° and = 45~90°,the maximum of the decrease rate of solid wall and jet is 17.2% and 21.3%.And the smaller the lobe aspect ratio,the better the infrared characteristic suppression effect;(3)The flow matching parameter selection is related to the mixer profile type.The flow matching parameters of the rotating axisymmetric mixer S-2D mixed exhaust system select the S-2D nozzle inlet diameter and the exhaust system exit area.The flow matching parameters of the non-rotating axisymmetric mixer S-2D mixing exhaust system select the mixer outlet area and the exhaust system outlet area;(4)The spoiler formed by the rotation of the propeller has a significant influence on the flow field characteristics and infrared characteristics of the turbo engine exhaust system,and the greater the propeller speed,the smaller the infrared radiation intensity of the turboprop exhaust system,compared with the static state.When the propeller speed is W=17r/s and 24r/s,the infrared radiation intensity of the turboprop exhaust system at azimuth angle of ?=90° is reduced by 30.4% and 44.6%.