Modeling And Simulation Of Infrared Radiation Characteristics Of Aircraft Skin Under Low Temperature Conditions

In recent years,with the improvement of the accuracy of infrared guided weapons,the stealth performance of fighter becomes more and more important.In order to prevent the aircraft from being detected by infrared instruments and avoid the attack of infrared guided weapons,it is necessary to develop a measurement method that can reflect the characteristic parameters of the target accurately and quickly.The infrared radiation characteristics of aircraft skin are calculated and analyzed to evaluate and improve the infrared stealth performance of aircraft.At present,it takes a long time,costs a lot and is difficult to obtain the infrared radiation characteristic data of aircraft through field test.Therefore,it is of great application value to obtain the infrared radiation characteristic data of aircraft through numerical simulation.Firstly,the infrared radiation characteristics of aircraft skin were simulated.A geometric model of a typical airplane was established by using CATIA software,and the GID software was used for grid division processing.Then the infrared radiation characteristics are modeled theoretically.The inverse monte carlo method is used to obtain the solar radiation heat flow.The whole aircraft model is discretized into several small elements by finite element method,and the complex reflection problem is transformed into discrete finite element problem for solving.Based on the theoretical model derived,the program for calculating the infrared radiation characteristics of aircraft is written in Fortran language.Secondly,this paper studies the emissivity measurement method of aircraft surface skin coating materials under low temperature environment.Based on the energy method,a emissivity measurement system with Fourier infrared spectrometer as the core is built.In order to avoid the influence of the radiation from the surrounding environment,the vacuum environment was built,and the background function of the spectrometer was modified to improve the reliability of the measurement results.The system makes the emissivity measurement environment consistent with the actual flight environment of aircraft,thus improving the practical application value of aircraft skin infrared radiation characteristics simulation.Finally,the emittance data of aircraft skin materials at different temperatures and wavebands are obtained by using the emittance measurement system,and the uncertainty is analyzed.At the same time,the three dimensional temperature field and infrared emission field in the bands of 3?5?m and 8?14?m are simulated by using the control variable method.Simulation results show that:(i)solar radiation has an obvious heating effect on the sunny side of aircraft skin,raising the skin temperature by nearly 30?.When the aircraft is in motion,the degree of temperature change is lower than the static state.Due to the aerodynamic effect,the temperature at the head and tail of the aircraft is relatively high;(ii)The infrared radiation energy of the skin is mainly concentrated in 8?14?m far infrared band,under the state of motion;(iii)the higher the flight height of the aircraft,the higher the emissivity of the skin material,and the stronger the infrared radiation performance.The increase of flight speed leads to the decrease of surface temperature field and the increase of infrared emission field.