Research On Infrared Radiation Performance Of Air Vehicle And Temperature Reduction Disciplinarian Of Engine Nacelle Skin

As a result of severe aerodynamic heating under supersonic flight conditions and internal heating from engine wall with high temperature, fuselage skin of air vehicle has become the main infrared radiation sources of 8-14μm band. Simultaneously, exhaust nozzles and visual components with high temperature inside of the engine chamber are the main infrared radiation sources of 3-5μm band. The above infrared radiations of air vehicle are precisely the targets which are detected and tracked by the infrared guidance weapons. With the development of infrared imaging detection technology for 8-14μm band in recent years, the detection and track mode is being changed from short wave of 3-5μm band to long wave band of 8-14μm, as well as from point-target detection to surface--target detection, resulting more and more serious threat for the combat aircrafts. Therefore the infrared stealth ability will become even important in the furture. The present paper carried out the research on infrared radiation performance of air vehicle and temperature reduction disciplinarian of engine nacelle skin, being of significant therotical and applied values. In this paper, the main research contents include the following several aspects:(1) Practical ways of modeling the aerodynamic heating under supersonic flight conditions, flow and heat transfer inside aero-engine nacelle, and plume heating on the rear fuselage of aircraft were introduced for simulating the aircraft skin temperature distributions for a simplified combat aircraft model. The detailed results of the flow field, the whole fuselage skin temperature field and infrared field were obtained and analyzed. The influences of flight Mach number, skin surface emissivity, as well as decreasing local temperature and emissivity on local zone with high temperature on the aircraft infrared radiation characteristics were studied.(2) Experimental system for investiagating the temperature reduction disciplinarian of engine nacelle skin was designed and processed. The effects of ventilation cooling, radiation shelter, heat conduction insulation and low emissivity layer application on the temperature reduction disciplinarian were experimentally studied. Numerical calculation and thermal analysis were also carried out to the experimental models and the temperature reduction disciplinarian with the use of different measures was obtained. At last, the temperature reduction effect of engine nacelle skin in the real environment of high altitude was numerically simulated and verified.(3) The infrared raditation characteristics of vehicle exhaust systems with axisymmetric nozzle and two-dimensional nozzle were numerically studied and the infrared suppression effect of two-dimensional nozzle on the infrared radiation of plume and engine chamber was obtained. The infrared characteristics of the exhaust systems with single-engine and twin-engine were compared, for the radiation intensity and distribution characteristics. Integration modification was also made to the exhaust system by adding extension and shielding structures on the nozzles. The consequent infrared suppression effect was researched.(4) Skin temperature and the plume flow fields for different scale models were calculated. By analizing the infrared radiation characteristics from the skin, plume and engine chamber in different scale models, the relationship between the scaling factor and the infrared radiation intensity of combat aircraft was preliminary discussed.(5) A scaled test model of aircraft was designed and processed. By using multi-channels temperature control system, local heating on the scaled test model was realized to simulate the aerodynamic heating temperature field. The skin temperature field was recorded by infrared thermal imaging system. Finally, the infrared radiance contours and infrared radiation intensity from different angle of views were calculated according to the thermal images. Tipical temperature distribution on the scaled test model was got by temperature control system, and the surface emissivity of the test model was changed by low emissivity coating. The effect of fuselage skin temperature and surface emissivity on the infrared radiation characteristics of aircraft was studied and verified by experimental methods.