Abstract Turbulent cryogenic nitrogen jets at transcritical and supercritical conditions are numerically investigated by LES-based multi-environment probability density function method together with the tabulated thermodynamic properties. To account for the non-ideal thermodynamic effects, the mixture properties are calculated by using Soave-Redlich-Kwong equation of state. The effect of sub-grid scale fluctuations of thermodynamic properties is modelled by the multi-environment PDF. Numerical results indicate that the present multi-environment PDF approach has the prediction capability to capture the essential features of cryogenic nitrogen jets under the supercritical pressure. Comparing with the supercritical jet, the transcritical jet features the longer and denser core which is relatively resilient to core destruction caused by turbulence. It is also found that the stronger pseudo-boiling strength and the larger density difference are directly tied with the longer cold-core length. In terms of the sub-grid scale scalar fluctuation, the transcritical jet shows the larger magnitude than the supercritical jet. In the transcritical nitrogen jet, it is identified that the strong sub-grid fluctuations of density and isobaric specific heat are closely tied with the pseudo boiling process. These numerical results suggest that the high-fidelity numerical modelling for transcritical flows must have the capability to realistically represent the combined effects of turbulence and thermodynamic nonlinearities, sub-grid scale fluctuations, and scalar conditional statistics.

中文翻译：

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基于大涡模拟的跨临界和超临界低温氮气射流混合过程的多环境 PDF 建模

摘要 采用基于 LES 的多环境概率密度函数方法以及表格热力学性质对跨临界和超临界条件下的湍流低温氮气射流进行了数值研究。考虑到非理想的热力学效应，混合物特性是通过使用 Soave-Redlich-Kwong 状态方程计算的。热力学特性的亚网格尺度波动的影响由多环境 PDF 建模。数值结果表明，目前的多环境 PDF 方法具有捕捉超临界压力下低温氮气射流基本特征的预测能力。与超临界射流相比，跨临界射流具有更长、更密集的核心，对湍流造成的核心破坏具有相对弹性。还发现更强的伪沸腾强度和更大的密度差异与更长的冷芯长度直接相关。在亚网格尺度标量涨落方面，跨临界射流比超临界射流表现出更大的幅度。在跨临界氮射流中，确定了密度和等压比热的强烈亚网格波动与伪沸腾过程密切相关。这些数值结果表明，跨临界流动的高保真数值建模必须能够真实地表示湍流和热力学非线性、亚网格尺度波动和标量条件统计的综合影响。