Numerical Simulation On Infrared Imageing Of High Speed Aerocraft

The infrared thermal image characteristics of high speed aircraft is one of vital indexs to its battle field surviving capacity.It not only is a premise for infrared hiding,detecting and giding technologies advancement,but also impacts battle modes.However,its generation and transportation mechanism is still not perfectly known which contributes to the lack of effective experimental studying tools.This is firstly in consequence of the complexity of its configuration.At the same time,the infrared radiation of high speed aircraft is influeced by numerous factors such as the high speed aerodynamic and its skin coupled heat transfers and the radiation properties.Thus,numerically studying the generation and transportation of the infrared radiation is the main method for retrieving the infrared image charectoristics of high speed aircraft.The research of this paper aims at establishing highly efficient numerical methods for analyzing the generation and transport of high speed aircraft infrared image and making clear the infrared characteristics of high speed aircraft and the factors impact on them.Firstly,considering the high amount of calculation of the Monte Carlo method in simulating the infrared radiation transport applying to sophicated configuration such as airplane,effective and fitting method has been studied.Through studying the sampling mode and stochastic features of the Monte Carlo method,a bidirectionally weighted Monte Carlo method has been composed.Then the standard deviations of the presented method and the forward and reverse Monte Carlo methods have been deduced.With the same numbers of sampling rays(the same amount calculations),the standard deviations of the four Monte Carlo methods applied to computing cases have been analyzed and the priority of the presented Monte Carlo method over the other three ones has been validated.More over,considering the infrared radiation of the plume of the high speed aircraft,the attenuation of the infrared image by the gas species CO2 and H2 O in the atmosphere,and the coupling between the radiation and the aerodynamic convection of heat and mass transfer of airplane,the methods for the radiation transfer in complex medium have been studied.In order to take the advantages of Monte Carlo method in its random sampling when treating the spectrum,the advantages of finite volume method in effectively discretizing the spetial and directional domains and the advantages of unstructured mesh in fitting for complex geometry,a hybrid unstructed finite volume/Monte Carlo method has been developed.Through computing cases analysis,the reliability and effectiveness of the presented method are validated.The temperature distribution is the infrared radiation source of high speed airplane,thus the simulation of the infrared image of it must be based on the precise temperature data of its body.This paper,through the analysis on the mechanism of the coupling between outer aerodynamic convective heat transfer and the inner heat transfer of the airplane skin,presents a decoupling calculation method of this coupled heat transfer and realizes the calculation of the transient conjugate heat transfer of airplane with large and sophicated configuration under high speed airflow.The reliability of this method is then validated by combining usage of the numerical method and wind tunnel experiment,and this method can be applied in precisely obtaining the temperature distribution of the body of high speed airplane.Based on the above infared radiation and temperature field calculation methods research,further analyzing the radiation transport mechanism during the process of infrared image detecting,considering the optical system effect of infrared image,the method for calculating the infrared image of high speed aircraft has been developed.Two ways for dealing with the concentration and image process of the equivalent radiation from high speed aircraft have been adopted.One is the equivalent radiation concentration method which firstly calculates the equivalent radiation of the high speed airplane and then its concentration and image process in the infrared detecting optical system.The other is the reverse Monte Carlo method which calculates the infrared radiation transfer process and the concentration and image process simultaneously.And in the reverse Monte Carlo method,the random spetrum sampling technique has been implemented to realize the infrared image calculation of high speed aircraft with nongray infrared hiding coating surface.Computing code has been composed according to the methods presented in this paper for numerically simulating the infrared image of high speed aircraft.Taking the third generation aircraft model SDM as the researching target,its temperature and infrared image process under high speed flying condition has been numerically simulated and analyzed.In addition,the exhaust plume temperature distribution,species mass fraction distribution and infrared image have also been numerically simulated and analyzed.Through the studies of this paper,the bidirectionally weighted Monte Carlo method fitting for the infrared radiation analysis of large and complicated configuration,the hybrid unstructured finite volume/Monte Carlo method in accordance with high speed aerodynamic convective heat and mass transfer computing code,and the decouping method for the conjugate heat transfer of the skin of high speed aircraft have been developed.These methods,together with the infrared radiation concentration and image process in infrared optical system simulating method,can be sequentially applied to the simulation and analysis of the infrared image characteristics of high speed aircraft and impacting factors on it.