高超声速飞行流场中的最大氧离解度分析

针对大气层内高超声速飞行时的化学非平衡现象，建立了沿驻点线流动的空气中氧离解度的计算模型. 模型假设氮气在氧气未充分离解时不发生离解，并且不涉及边界层内的复合反应. 理论计算发现，空气中氧的离解度随飞行高度的增加呈先增后减的非单调变化规律，其原因是由于化学反应平衡移动与非平衡效应相互作用的结果. 这一结论得到了数值模拟结果的验证，同时也解释了文献中当飞行高度较高时真实气体效应减弱的现象. 基于驻点线的近似理论模型，计算得到了轴对称钝头体绕流流场中的最大氧离解度及边界层外缘温度随飞行速度和高度变化的等值线图谱，相关结果可以为工程设计所用. 

ANALYSIS OF MAXIMUM DISSOCIATION DEGREE OF OXYGEN DURING HYPERSONIC FLIGHT

A theoretical model is established to calculate the dissociation degree of oxygen along the stagnant streamline of airflow, which is used to study the chemical nonequilibrium phenomena during hypersonic flight. The model assumes that nitrogen will not dissociate before oxygen undergoes serious dissociation. The recombination reaction in the boundary layer is also excluded in the model. It is found that, the dissociation degree of oxygen first increases and then decreases as the flight altitude increases, which is due to the competence between the equilibrium shift and nonequilibrium effect. This observation is confirmed by CFD simulations, and can be used to explain the phenomenon of the decline of real gas effects with increasing flight altitude in the literature. Using the developed model, the maximum dissociation degree of oxygen and temperature at the external edge of the boundary layer, are evaluated for hypersonic flows over a blunt body that cover a wide range of flight speeds and altitudes. The results are useful for engineering applications.