Line By Line Calculations Of Radiative Properties Of High-temperature Gases

High-temperature gas radiation has been applied in many research fields,such as TDLAS technology in combustion measurement,high-temperature shock tube spectral diagnosis technology,aerodynamic radiative heating calculations for hypersonic vehicles,and optical detection of high-speed targets.These applications require full acquisition of the radiative properties of high-temperature media.For most complex plasma environments,radiation modeling is not only a simple electronic transition process,but also takes into account the thermodynamic state of gas and various complex physical and chemical processes between species,which makes radiation modeling became a big challenge.Although previous publications have reported on the modeling of high-temperature gas radiation,previous research mainly has the following gaps:(1)Most of the processing of partition functions only uses low-lying electronic states,and even higher electronic states under high temperature conditions can contribute to the partition function.Therefore,the partition function values in the literatures limit their applications at high temperatures.(2)Most of the studies on transition probability are based on the earlier experimental spectral constants and theoretical electron transition dipole moment,and most of them are transitions of low vibrational energy levels,which makes the calculated transition probability data incomplete.(3)In the study of electron collision broadening of atoms,most studies overlook the contribution of this broadening or use limited experimental data to fit a simple expression to calculate the line width.These treatments cannot accurately construct electron collision line width values,especially for the contribution of electron collision broadening in hightemperature applications that cannot be ignored.(4)In energy level calculation,some research work only uses Damhum expression to obtain the vibrational rotational energy levels of diatomic gas,which ignores the fine structure of energy levels.In fact,for states with Λ≠ 0,each rotational energy level will split into two energy levels(Λ double splitting),and the energy level spacing will increase as the rotation becomes faster.To improve the above issues and construct a comprehensive and accurate radiation properties basic database,this article focuses on the Earth’s atmosphere and Mars’ atmospheric plasma as research objects,and conducts more detailed modeling research around the hightemperature non-equilibrium characteristics of plasma.The specific work includes:(a)Perform high-precision reconstruction of the thermodynamic properties,especially the partition function,of high-temperature gases.For the atomic partition function,this article adopts the "multi group theory" calculation method,which not only simplifies the computational complexity,but also obtains calculation results comparable to accurate calculation methods.For diatomic gas,this paper uses a more rigorous solution of the Schrodinger equation to obtain energy levels.In this process,the latest electronic state data from literature was utilized and more electrons were considered to make the calculation results applicable to higher temperatures.Overall,the error between the calculated data and literature for atomic components in this article is less than 8%;For most components of diatomic components,the error does not exceed 20%.(b)Accurately determine the transition probability size that characterizes the radiation characteristics of gases.Based on the recently published ab initio spectral constants and electronic Transition dipole moment,a more complete database of transition probabilities is reconstructed by using a semi empirical method.Finally,the calculation results of this paper were verified by comparing the vibration energy level lifetimes measured experimentally and theoretically in literature;From the perspective of accuracy,the results of this article are mostly in good agreement with the theoretical and experimental data in the literature.Even if they are not well consistent with the experimental data,most of them fall within the error range of experimental measurements.(c)Detailed calculations were conducted on the spectral line width and linetype,with a focus on the Stark broadening effects of atoms and ions that were not previously considered.Firstly,the required transition parameters were obtained by solving the atomic structure using the ab initio algorithm,and then the Stark linewidth was directly calculated using a semi empirical method.By comparing the results with literature,this article obtained line width data with good accuracy.Due to the semi empirical method used in Stark calculations in this article,this method has good accuracy in the short wave region under certain conditions but not high accuracy in the long wave region.(d)Accurate reconstruction of continuous and discrete spectral radiation of high-temperature gases.Through the above work,combined with the knowledge of Spectroscopy,quantum mechanics and Statistical mechanics,the radiation characteristics of high-temperature gas were verified and calculated.From the verification results,it can be seen that the radiation source intensity calculated in this article is in good agreement with the experimental results in the literature,with an error of less than 26.2% compared to the numerical radiation source intensity in the literature,and has good consistency with the total air absorption coefficient in the literature.(e)Use the constructed radiation characteristic data to predict the radiation heat flux during the re-entry process of the aircraft.This article systematically studies the radiation heating of two spacecraft,RAMC-II and Mars Science Experiment MSL,under actual flight conditions.From the calculation results,it can be seen that for the RAMC-II aircraft,the areas with strong radiation are mainly located near the head stagnation zone,and the calculated heat flows at three flight altitudes(61 km,71 km,and 81 km)are in good agreement with the literature results,which to some extent verifies the reliability of the calculation method.For MSL aircraft,its Radiant flux is also large in the stagnation region,and the calculated radiant heat flow is relative to the convective heat flow value obtained by computational fluid dynamics method,but the value is smaller than the convective heat flow.