Abstract Rocket engines and high-power new generations of gas-turbine jet engines and diesel engines oftentimes involve the injection of one or more reactants at subcritical temperatures into combustor environments at high pressures, and more particularly at pressures higher than those corresponding to the critical points of the individual components of the mixture, which typically range from 13 to 50 bars for most propellants. This class of trajectories in the thermodynamic space has been traditionally referred to as transcritical. However, the fundamental understanding of fuel atomization, vaporization, mixing, and combustion processes at such high pressures remains elusive. In particular, whereas fuel sprays are relatively well characterized at normal pressures, analyses of dispersion of fuel in high-pressure combustors are hindered by the limited experimental diagnostics and theoretical formulations available. The description of the thermodynamics of hydrocarbon-fueled mixtures employed in chemical propulsion systems is complex and involves mixing-induced phenomena, including an elevation of the critical point whereby the coexistence region of the mixture extends up to pressures much larger than the critical pressures of the individual components. As a result, interfaces subject to surface-tension forces may persist in multicomponent systems despite the high pressures, and may give rise to unexpected spray-like atomization dynamics that are otherwise absent in monocomponent systems above their critical point. In this article, the current understanding of this phenomenon is reviewed within the context of propulsion systems fueled by heavy hydrocarbons. Emphasis is made on analytical descriptions at mesoscopic scales of interest for computational fluid dynamics. In particular, a set of modifications of the constitutive laws in the Navier–Stokes equations for multicomponent flows, supplemented with a high-pressure equation of state and appropriate redefinitions of the thermodynamic potentials, are introduced in this work based on an extended version of the diffuse-interface theory of van der Waals. The resulting formulation involves revisited forms of the stress tensor and transport fluxes of heat and species, and enables a description of the mesoscopic volumetric effects induced by transcritical interfaces consistently with the thermodynamic phase diagram of the mixture at high pressures. Applications of the theory are illustrated in canonical problems, including dodecane/nitrogen transcritical interfaces in non-isothermal systems. The results indicate that a transcritical interface is formed between the propellant streams that persists downstream of the injection orifice over distances of the same order as the characteristic thermal-entrance length of the fuel stream. The transcritical interface vanishes at an edge that gives rise to a fully supercritical mixing layer.

中文翻译：

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化学推进系统高压燃烧器中推进剂的跨临界扩散界面流体动力学

摘要 火箭发动机和新一代大功率燃气轮机喷气发动机和柴油发动机经常涉及将一种或多种亚临界温度的反应物喷射到高压下的燃烧室环境中，尤其是在高于对应于临界点的压力下的压力。对于大多数推进剂，混合物的各个组分的压力范围通常为 13 到 50 巴。热力学空间中的这类轨迹传统上被称为跨临界轨迹。然而，对如此高压下的燃料雾化、汽化、混合和燃烧过程的基本理解仍然难以捉摸。特别是，虽然燃料喷雾在常压下的特征相对较好，由于可用的实验诊断和理论公式有限，对高压燃烧器中燃料分散的分析受到阻碍。化学推进系统中使用的碳氢化合物燃料混合物的热力学描述很复杂，涉及混合诱发的现象，包括临界点的升高，由此混合物的共存区域延伸到远大于临界压力的压力。单个组件。因此，尽管存在高压，承受表面张力的界面可能会在多组分系统中持续存在，并且可能会产生意想不到的喷雾状雾化动力学，否则单组分系统在临界点以上是不存在的。在本文中，目前对这种现象的理解是在以重碳氢化合物为燃料的推进系统的背景下进行审查的。重点是对计算流体动力学感兴趣的细观尺度的分析描述。特别是，基于扩展版本的多组分流动的纳维-斯托克斯方程中的一组本构定律的修改，辅以高压状态方程和热力学势的适当重新定义，在这项工作中被引入。范德瓦尔斯的扩散界面理论。由此产生的公式涉及重新审视应力张量和热量和物种的传输通量的形式，并能够描述由跨临界界面引起的细观体积效应，与高压下混合物的热力学相图一致。该理论的应用在典型问题中得到了说明，包括非等温系统中的十二烷/氮跨临界界面。结果表明在推进剂流之间形成了跨临界界面，该界面在喷射孔下游持续存在与燃料流的特征热入口长度相同数量级的距离。跨临界界面在产生完全超临界混合层的边缘处消失。结果表明在推进剂流之间形成了跨临界界面，该界面在喷射孔下游持续存在与燃料流的特征热入口长度相同数量级的距离。跨临界界面在产生完全超临界混合层的边缘处消失。结果表明在推进剂流之间形成了跨临界界面，该界面在喷射孔下游持续存在与燃料流的特征热入口长度相同数量级的距离。跨临界界面在产生完全超临界混合层的边缘处消失。