We study the effect of phase separation in multi-component mixing at super-critical conditions using a novel framework based on vapor-liquid equilibrium (VLE) thermodynamics in a real gas mixture. This approach is combined with a non-conservative Double-Flux (DF) numerical model to overcome numerical instabilities that arise when high-pressure, low-temperature mixtures are considered. The formulation developed and validated can handle VLE in multi-component mixtures even though most of the initial studies are focussed on binary mixtures. The challenges to get a robust solution of VLE thermodynamics are highlighted and we demonstrate the ability and the accuracy of the algorithms to account for VLE in canonical test cases, as well as in a shear layer binary mixing in a canonical temporal-mixing layer. Results are also compared against the classical, “dense-fluid” approach where an equation of state (EoS) is used with the assumption of a single-phase within each computational cell. Differences are highlighted and explained from a thermodynamic point of view with emphasis on the relevance and the applicability of VLE.

中文翻译：

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超临界条件下多组分混合过程中相分离的数值研究

我们使用基于真实气体混合物中气液平衡 (VLE) 热力学的新型框架研究了超临界条件下多组分混合中相分离的影响。这种方法与非保守双通量 (DF) 数值模型相结合，以克服在考虑高压、低温混合物时出现的数值不稳定性。尽管大多数初始研究都集中在二元混合物上，但开发和验证的配方可以处理多组分混合物中的 VLE。强调了获得 VLE 热力学稳健解决方案的挑战，我们展示了算法在规范测试案例中以及在规范时间混合层中的剪切层二进制混合中解释 VLE 的能力和准确性。结果也与经典比较，“稠密流体”方法，其中使用状态方程 (EoS) 并假设每个计算单元内为单相。从热力学的角度突出并解释了差异，重点是 VLE 的相关性和适用性。