态-态模型下的O2/O系统热化学非平衡与辐射过程

Numerical study of thermo-chemical nonequilibrium and radiation process for O2/O system with state-to-state approach

采用态-态模型,研究包含振动能级跃迁、化学反应和辐射跃迁的O2/O系统的非平衡过渡过程。对静止的O2/O气体系统,设定不同的初始条件,突然降温或升温至3000K、10 000K、20 000K后保持等温等容,数值模拟组元质量分数、振动能级分布和辐射特性随时间的演化过程,分析不同条件下各类过程趋近平衡的松弛时间、稳态平衡结果等特征,以及辐射和热化学非平衡过程的相互影响特点。结果表明,态-态模型得到的振动温度趋近平衡值的特点与双温度模型所描述的不同,有时振动温度随时间甚至出现非单调变化的现象,非平衡过渡过程中的振动能级分布也不满足振动温度下的玻尔兹曼分布。本文算例显示出O2/O系统在高温条件下的非平衡辐射特征,不过辐射跃迁对热化学非平衡过程的影响不明显,非平衡辐射的特征时间达到振动松弛时间的10倍以上。

The state-to-state approach,which includes the transitions between vibrational energy levels,state specific chemical reactions,and radiative transitions,is used to study the nonequilibrium process of O2/O mixture system.The time evolution of the density of O and O2 at specific energy levels as well as the radiative band intensities are numerically simulated for a stationary closed O2/O mixture system with different initial conditions at constant governing temperature and volume.The transient properties such as the relaxation time and the equilibrium steady state values of the nonequilibrium processes are analyzed,and the interactions between the vibrational transitions,chemical reactions,and the radiative transitions are discussed.The results show that,the time evolution of the vibrational temperature does not follow the exponential approaching behavior described by the two-temperature model,the vibrational temperature even show non-monotonous variation with time,and the population distributions of the vibrational energy levels also depart from the Boltzmann distribution under the vibrational temperatures.The radiation properties show strong nonequilibrium feature in the transient process for the cases at high temperature,however,the effects of the radiation on the thermo-chemical processes are not evident,and the characteristic time of nonequilibrium radiation is one order of magnitude higher than the vibrational relaxation time.