Study On The Thermochemical Non-equilibrium Flow Field And The Spectral Radiation Characteristics Of The Plume Of Hypersonic Vehicle

During the flight of a hypersonic vehicle,the air around the head is severely compressed,and the kinetic energy is converted into internal energy,resulting in a sharp increase in the temperature of the surrounding flow field.Atoms and molecules in the air undergo complex chemical reactions at high temperatures,and the intense ultraviolet spectrum radiated by these chemical reactions has important research significance for space-based ultraviolet detection and interception early warning.In addition to the aircraft model itself,the factors affecting the calculation results of ultraviolet radiation include the thermodynamic model of the flow field and the chemical reaction model.At the same time,the thermal protection material continuously peels off and undergoes complex chemical reactions with high-temperature air during the flight to generate a large number of new ultraviolet radiation molecules,which greatly enhances the detectability of the ultraviolet radiation of the shock layer.There are also ultraviolet radiation molecules in the tail flame flow field.The selection of different tail flame fuels and chemical reaction models has an important impact on the precise positioning of the ultraviolet band when space-based detection of tail flame targets.In this thesis,based on the shock layer and tail flame flow field of hypersonic vehicle,the line-of-sight integration method of one-dimensional path gas radiative transmission is adopted.Considering the characteristics of non-uniform physical environment of shock layer,a variety of non-uniform stratification methods are combined with line-of-sight integration method.The results of mesh adaptive non-uniform stratification are the most accurate after error calculation and analysis.Finally,the line of sight integration method of adaptive mesh layering is extended to two-dimensional case,and the tail flame calculation model of adaptive mesh non-uniform slice is designed.The main contents of the paper are as follows:1)Modeling and simulation of shock layer and plume flow field of aircraftConsidering that the flow field structure and spectral radiation values calculated by different aircraft models are different,a two-temperature thermochemical non-equilibrium model is adopted to simulate the shock layer flow field of blunt and pointed conical hypersonic vehicles based on computational fluid dynamics.The parameters of the shock laminar flow field under different flight speeds,altitudes and angles of attack are analyzed,and the effects of different air chemical reaction models on the shock laminar flow field are studied.In the plume flow problem,the BEM engine tail flame and n-pentane combustion tail flame are simulated respectively,and the plume flow field parameter cloud map is obtained.In this thesis,a grid slice model of plume is proposed to calculate the ULTRAVIOLET radiance of tail flame mixed gas at different sight angles.The results show that NO,OH and CO are the main ultraviolet radiation sources of tail flame in these two chemical reaction models.2)Improved non-uniform stratified line of sight integration method and adaptive grid transverse longitudinal slice plume radiance calculation modelIn the process of solving the line of sight integral method of gas radiative transport,the stratification method lacks criterion.Based on the gradient distribution of temperature,pressure and mole fraction of components in the shock laminar flow field,the parameters of the shock laminar flow field change dramatically in a short distance.The non-uniform transmission distance of each section is determined by weighting the gradient change rate,and the flow field parameters and the non-uniform distance are put into the radiative transmission equation.The adaptive grid is designed for the shock wave position and was exponentially encrypted near the wall.The adaptive grid spacing is selected as the basis for non-uniform layering of the line of sight integral method,and the grid node parameters on the stagnation line are extracted into the line of sight integral equation for calculation.The results show that the error between the calculation result and the experiment is the smallest,and the error is only 30.7%of the uniform error.A transverse and longitudinal mesh slice model is established for the calculation of tail flame radiation,and an adaptive mesh non-uniform slice was carried out for the two-dimensional flow field.The parameter information of intersections with all horizontal and vertical mesh slices is obtained along the line of sight.The correctness of the model is further verified by degradation verification,which provides an accurate and efficient method for calculating the ULTRAVIOLET radiance of any line of sight mixed gas in the tail flame flow field by non-uniform stratified line of sight integration.3)C-C thermal protection material ablates shock layer gas UV radiationBased on the thirty-four ablation chemical reaction model of C-C thermal protection material and the experimental data of C-C ablation flow field in literature,the ULTRAVIOLET radiance of hypersonic shock layer mixture gas under high temperature ablation of C-C thermal protection material is calculated by using the line integral method of adaptive non-uniform grid.At high temperatures,the C atoms sublimate into soot gas,and the C atoms react to form C₂ molecules,which also combine with N and O atoms in the air to form CN and CO molecules.In the ablative flow field,C,C₂,NO,CO and CN atoms and molecules are the main sources of ULTRAVIOLET radiation in the band of100-400nm,and the detectable band range is increased compared with that of NO molecules in the air when only ultraviolet radiation is considered without ablative.The results show that the ultraviolet radiance of C-C ablated shock layer is two orders of magnitude higher than that of the non-ablated case,and the highest radiance is the discontinuous transition radiation of C atom.Secondly,the radiation of CO molecule in ultraviolet continuous band is dominant,and the uv radiance of the shock layer increases obviously with the increase of ablation time,which greatly improves the detectability of the shock layer in ultraviolet band.