Spectral Radiation Characteristics Of Non-Equilibrium Flow Field Of Blunt Body Entering Mars Atmosphere

When a hypersonic aircraft enters the atmosphere,a shock layer will be formed in the front of the aircraft.The temperature and pressure of the gas will rise sharply behind the shock,forming a high-temperature thermochemical non-equilibrium reaction flow with strong thermal radiation,which causes the surface of the aircraft to be ablated and influence the communication system of the aircraft.In order to obtain the reliable heat flow data on the surface of the aircraft and to design a reasonable thermal protection system,it is necessary to study the mechanism of formation and radiation characteristics of the thermal chemical non-equilibrium gas behind the shock layer in the front of the aircraft.Based on the two-temperature chemical model from Park,the thermal chemical non-equilibrium gas behind the shock layer of the Mars Pathfinder is researched with the CFD-FASTRAN software in this paper.Subsequently,the radiation characteristics of a feature point under non-equilibrium conditions are studied.For the 8 components?flight heights of 41.7km?and 14 components?flight heights of 40.7km,32.0km and 27.7km?,the flow-field in the front of the Mars Pathfinder is simulated with CFD-FASTRAN software based on the flight test data obtained when the aircraft enters the Mars atmosphere.The simulated temperature and the main components?CO₂,CO,O?are compared with those of the literature.The two parameters are in good agreement,which proves the reliability of the data obtained from the simulation of the flow-field in the front of the aircraft.By analyzing the flow field data of the 14 components?flight height 40.7km?,it will be found that the temperature and pressure of the gas rises sharply behind the shock.The mass fraction of CO₂ molecules decreases from 95.6%to 0.41%.The mass fraction of CO increases from 0 to 60.6%.The mass fraction of O increases from 0to 35.8%.With the gradual descent of the flight height?40.7km,32.0km,27.7km?,the peak value of the translational temperature is 9457 K,6049K and 4847 K.The peak value of the vibration temperature is 7068 K,4948K and 4252 K in turn,indicating that the non equilibrium degree decreases behind the shock.The non-equilibrium characteristics of the gas in the front of the aircraft are significant at the height of 40.7km from Mars.In this paper,we choose the point of stagnation line?T_r=9457K,T_v=2576K?to study the spectral radiation characteristics of the gas after shock wave.The analysis shows that the bound-bound transition mechanism dominates the spectral line when the wavelength is bigger than 0.125?m.In the range of 0.083-0.125?m wavelength,the bound-free transition mechanism affects dominance.The free-free transition mechanism has little effect on the gas radiation characteristics behind the shock layer.For the bound-bound transition,the Red electronic system of the CN molecule and the IR electronic system of the CO molecule have a good influence on the spectral lines in the infrared band.In the visible light band,the Violet electronic system of the CN molecule and the Schumann-Runge electronic system of the O₂ molecule are dominant to the spectral lines.In the ultraviolet band,the Fourth positive systemthe of CO molecule,the Schumann-Runge electronic system of O₂ molecules and the most of the electronic systems??,?,?,?,b',?'? of NO molecule are of great influence on the spectra.