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/离解温度，并发生显着的热化学弛豫过程。热化学非平衡现象会影响混合和燃烧过程，成为超燃冲压发动机设计必须考虑的因素。本文开发了一种基于二温模型的大涡模拟求解器。振动能量和跨旋转能量之间的传递项采用 Landau-Teller 公式建模，并采用 Park 模型考虑振动-解离耦合。基于Hyshot Ⅱ发动机配置不同型号的三组模拟同时进行，以验证数值方法并分析结果。结果表明，激波、燃料交叉喷射和普朗特-迈耶流会产生显着的非平衡区域。射流混合区的振动弛豫过程被冻结，振动温度远高于跨转温度，多余的能量从振动模式转换为跨转模式，导致跨转温度升高。旋转温度和非平衡条件下自燃的提前。考虑到振动-解离耦合，较高的振动温度会促进解离。它抑制着火过程中活性自由基的产生，减弱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转转温度略低于平衡情况。