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Assessment by comparison with DNS data of turbulence models used in simulations of mixed convection

机译：通过与DNS数据比较评估混合对流模拟中使用的湍流模型

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The paper presents an assessment of the performance of a variety of turbulence models in simulating buoyancy-aided, turbulent mixed convection in vertical pipes. This has been done by comparison of RANS predictions with DNS results already available in the literature. Both the RANS and the DNS studies were conducted for conditions of constant and uniform fluid properties with the influence of buoyancy being accounted for using the Boussinesq approximation. This eliminated effects of non-uniformity of properties other than through the action of buoyancy and enabled its influence to be considered in isolation. In the course of the study, the turbulence models have been classified into two groups, namely, those which were able to capture the main features of buoyancy-influenced heat transfer (Group one) and those that were not able to do so (Group two). Common features in model formulation have been identified for each group. It is shown that the response to buoyancy of commonly-used controlling parameters in turbulence damping functions varies significantly and that the performance of a model can largely be correlated with the type of controlling parameter used. A significant defect of the Group-one models which has been identified is that they continue to predict that the 'viscous sub-layer' remains thick as a result of the influence of buoyancy even when the velocity profile has been distorted to an extent that it has become inverted in the core, whereas DNS data clearly show that this is not the case. The use of different methodologies for modelling direct production of turbulence through the direct action of buoyancy has been shown to have little effect on predictions of mixed convection in vertical flows because the effect of buoyancy on turbulence is predominantly due to the indirect effect.
机译：本文提出了对各种湍流模型在模拟垂直管道中的浮力辅助，湍流混合对流中性能的评估。这是通过将RANS预测与文献中已有的DNS结果进行比较来完成的。 RANS和DNS研究都是针对恒定和均匀流体性质的条件进行的，其中使用Boussinesq逼近法考虑了浮力的影响。除了浮力作用之外，这消除了特性不均匀性的影响，并使孤立地考虑其影响。在研究过程中，湍流模型分为两类，即能够捕获浮力影响的热传递的主要特征的模型（第一组）和不能捕获浮力影响的热传递的模型（第二组）。 ）。已经为每组确定了模型制定中的共同特征。结果表明，湍流阻尼函数中常用控制参数对浮力的响应变化很大，并且模型的性能在很大程度上与所用控制参数的类型相关。已经确定的第一组模型的一个重大缺陷是，他们继续预测“粘性子层”由于浮力的影响而保持较厚，即使速度分布已失真到一定程度也是如此。已经成为核心的倒置，而DNS数据清楚地表明并非如此。由于采用浮力对湍流的影响主要是由于间接影响，因此使用不同的方法通过浮力的直接作用对湍流的直接产生进行建模对预测对流的混合对流几乎没有影响。

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