As the Mach number increases, the local static temperature gradually approaches the characteristic gas vibration/dissociation temperature, and significant thermo-chemical relaxation processes occur. The thermo-chemical nonequilibrium phenomenona could affect the mixing and combustion process and become a factor that must be considered for scramjet design. In this paper, a large eddy simulation solver based on the two-temperature model is developed. The transfer terms between vibrational and trans-rotational energy are modeled by the Landau–Teller formulation and the vibrational-dissociation coupling is considered by adopting the Park model. Three sets of simulations based on the Hyshot Ⅱ engine configuration with different models were performed simultaneously to validate numerical methods and analyze results. The results reveal that the shock, cross-injection of fuel, and Prandtl-Meyer flow induce significant nonequilibrium regions. The vibration relaxation process in the jet mixing region is frozen, the vibration temperature is much higher than the trans-rotational temperature, and the extra energy is converted from the vibration mode to the trans-rotational mode, resulting in the increase of the trans-rotational temperature and the advance of auto-ignition in the nonequilibrium condition. Considering the vibration-dissociation coupling, the higher vibration temperature promotes dissociation. It inhibits the generation of active radicals in the ignition process, weakening the enhancement effect of nonequilibrium on auto-ignition. In the expanded nozzle, the concentrations of molecules and trans-rotational temperature in nonequilibrium cases are slightly lower than those in the equilibrium case due to the enhancement of dissociation.

中文翻译：

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热化学非平衡对超燃冲压发动机中横向射流燃烧特性的影响


随着马赫数的增加，局部静态温度逐渐接近特征气体振动/解离温度，并发生显著的热化学弛豫过程。热化学非平衡现象会影响混合和燃烧过程，并成为超燃冲压发动机设计必须考虑的一个因素。本文开发了一种基于双温度模型的大型涡模拟求解器。振动能和反式旋转能之间的传递项由 Landau-Teller 公式建模，振动-解离耦合采用 Park 模型考虑。基于Hyshot II.发动机配置的三组仿真，用不同的模型同时进行仿真，以验证数值方法并分析结果。结果表明，激波、燃料交叉喷射和 Prandtl-Meyer 流诱导了显著的非平衡区域。射流混合区的振动松弛过程被冻结，振动温度远高于反式旋转温度，多余的能量从振动模式转化为反式旋转模式，导致反式旋转温度升高，非平衡条件下自燃提前。考虑到振动-解离耦合，较高的振动温度会促进解离。它抑制了点火过程中活性自由基的产生，削弱了非平衡对自燃的增强作用。在膨胀喷嘴中，由于解离的增强，非平衡情况下的分子浓度和反式旋转温度略低于平衡情况下的分子浓度和反式旋转温度。