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首页> 外文期刊>International Journal of Heat and Mass Transfer >Derivation of a macroscopic mixture model for two-phase turbulent flows
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Derivation of a macroscopic mixture model for two-phase turbulent flows

机译：两相湍流宏观混合模型的衍生

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This article addresses the issue of reduced models to describe turbulent two-phase flows in industrial applications. A spatially-averaged mixture or drift-flux model is derived theoretically from the local instantaneous Navier-Stokes description. Reynolds-averaging and space-averaging are applied successively. Between these two steps, a model reduction is achieved to account for the non-equilibrium between phases via algebraic relations. Applications of this work are not limited to porous media but also include macroscopic descriptions to model high-shear regions developing near the walls for internal flows. Thermal effects, heat transfer at the wall and phase-change are also considered and briefly discussed. The final model describes the evolution of mixture variables, including effects of both sub-filter spatial variations, turbulence, and local non-equilibrium in velocity, pressure and enthalpy. This analysis provides bridges between different approaches to model two-phase flows (local instantaneous description, two-fluid model, local drift-flux model and spatially-averaged drift-flux model). It clarifies the content of each model involved by defining them in terms of local instantaneous quantities. Turbulent fluctuations and phase intermittency are crucial mechanisms. Important effects to model also include void fraction dispersion and turbulent diffusion; then, it is necessary to model the relative velocity, including the drift velocity orthogonal to gravity induced by the complex interactions between turbulent velocity fluctuations and the interfacial momentum transfer.The final macroscopic (spatially-averaged) mixture formulation is open, in the sense that expressions to model the various terms representing the physics of the small scales are not provided; instead, the physical sense and the origin of these models are discussed. The paper is meant as a basis on which analyses on local imbalance assumptions or relative velocity closures can be assessed. CFD simulations can provide information to complement experiments in technically challenging physical conditions or on processes essential to the models yet difficult to access experimentally (such as interfacial transfers for instance). Different kinds of two-fluid models can be tested to analyse their consequences on the macroscopic spatially-averaged model. In addition, a new path to calibrate closure laws or propose new models is opened based on finer-scale descriptions. Guidelines to use fine simulations along with the open expressions to derive closure relations either for the local drift-flux or for the spatially-averaged models are presented. They concern the modelling of the local relative velocity, the spatial average of the diffusion of void fraction and of the pressure drop.
机译：本文涉及减少模型的问题，以描述工业应用中的湍流两相流量。从本地瞬时的Navier-Stokes描述理论上从本地瞬间推导出空间平均混合物或漂移助熔剂模型。雷诺平均和空间平均是连续应用的。在这两个步骤之间，实现了模型减少，以通过代数关系解释相位之间的非平衡。该工作的应用不限于多孔介质，而且还包括宏观描述，以模拟在墙壁附近的内部流动附近的高剪切区域。热效应，墙壁和相变的热传递也被考虑并简要讨论。最终模型描述了混合物变量的演变，包括子过滤器空间变化，湍流和局部非平衡的效果，包括速度，压力和焓。该分析提供了不同方法与模型两相流动的桥梁（局部瞬时描述，双流体模型，局部漂移通量模型和空间平均漂移通量模型）。它阐明了在局部瞬时数量方面定义它们所涉及的每个模型的内容。湍流波动和相间隔是关键机制。对模型的重要效果还包括空隙分数和湍流扩散;然后，必须模拟相对速度，包括由湍流速度波动和界面动量转移之间的复杂相互作用诱导的与重力突出的漂移速度。最终宏观（空间平均）混合物配方在意义上是开放的为了模拟代表小尺度物理物理的各种术语的表达是;相反，讨论了物理意义和这些模型的起源。本文的意思是可以评估局部不平衡假设或相对速度闭合的分析。 CFD模拟可以提供有关在技术上挑战物理条件的补充实验的信息，或者对模型至关重要的工艺，难以通过实验进入（例如界面转移）。可以测试不同种类的双流体模型，以分析它们对宏观空间平均模型的后果。此外，基于更精细的尺度描述，打开校准闭合法律或提出新模型的新路径。使用微量模拟的指导方针以及用于派对局部漂移通量或空间平均模型的闭合关系的指南。他们涉及局部相对速度的建模，空隙分数和压降扩散的空间平均值。

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