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首页> 外文会议>ASME(American Society of Mechanical Engineers) Turbo Expo vol.4 pt.A; 20070514-17; Montreal(CA) >EVALUATION OF TWO-EQUATION MODELS OF TURBULENCE IN PREDICTING FILM COOLING PERFORMANCE UNDER HIGH FREE STREAM TURBULENCE
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EVALUATION OF TWO-EQUATION MODELS OF TURBULENCE IN PREDICTING FILM COOLING PERFORMANCE UNDER HIGH FREE STREAM TURBULENCE

机译：高自由度湍流预测膜冷却性能的两种湍流方程模型的评估

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The capabilities of four two-equation turbulence models in predicting film cooling effectiveness under high free stream turbulence(FST) intensity(Tu=10%) were investigated and their performance are presented and discussed. The four turbulence models are: the standard k-ε, RNG, and realizable k-e models as well as the standard k-ω model all four found in the FLUENT CFD code. In all models, the enhanced wall treatment has been used to resolve the flow near solid boundaries. A systematic approach has been followed in the computational setup to insure grid-independence and accurate solution that reflects the true capabilities of these models. Exact geometrical and flow-field replicas of an experimental study on discrete hole film cooling were generated and used in FLUENT. A pitch-to-diameter ratio of 3.04, injection tube length-to-diameter ratio of 4.6 and density ratios of 0.92 and 0.97 were some of the parameters used in the film cooling analysis. The study covered two levels of blowing ratios (M = 0.5 and 1.5) at an environment of what is defined as high initial free-stream turbulence intensity (Tu = 10%). Performance of these models under a very low initial FST were presented in a paper by the authors in Turbo Expo 2006. In that case, the standard k-ε model had the most consistent performance among all considered turbulence models and the best centerline film cooling effectiveness predictions under very low FST. However, after the addition of high FST in the free-stream, even the standard k-e model started to deviate greatly from the experimental data (up to 200% over-prediction) under high blowing ratios (M=1.5). The model which performed the best under high FST but low blowing ratios (M=0.5) is still the standard k-e model. In all cases only standard k-e model results match the trends of data for both cases. It can be said that under high FST with high M all the models do not do a good job of predicting the data. It was concluded that these deviations resulted from the effects of both high FST and high M. Under high M, near the injection holes deviations could result from the limitations of Boussinesq hypothesis relating the direction of Reynolds stress to the mean strain rate. Also, it seems like all models have trouble including the effects of high FST by not being able to take into account high levels of diffusion of turbulence from the free stream.
机译：研究了四个两方程湍流模型在高自由流湍流（FST）强度（Tu = 10％）下预测薄膜冷却效果的能力，并介绍和讨论了它们的性能。四个湍流模型是：在FLUENT CFD代码中找到的所有四个标准k-ε，RNG和可实现k-e模型以及标准k-ω模型。在所有模型中，都使用增强的壁处理来解决靠近固体边界的流动。在计算设置中遵循了系统的方法，以确保网格独立性和能够反映这些模型的真实功能的准确解决方案。产生了离散孔膜冷却实验研究的精确几何和流场副本，并将其用于FLUENT。膜冷却分析中使用的一些参数是螺距与直径之比为3.04，注射管长度与直径之比为4.6，密度比为0.92和0.97。这项研究涵盖了在所谓的高初始自由流湍流强度（Tu = 10％）的环境下的两个吹风比水平（M = 0.5和1.5）。作者在2006年Turbo Expo上的论文中介绍了这些模型在非常低的初始FST下的性能。在这种情况下，标准k-ε模型在所有考虑的湍流模型中具有最一致的性能，并且中心线胶片冷却效果最佳。 FST非常低的情况下的预测。但是，在自由流中添加了高FST之后，即使是标准k-e模型，在高鼓风比（M = 1.5）下也开始与实验数据（高达200％的超额预测）大相径庭。在高FST但低吹气比（M = 0.5）下表现最佳的模型仍然是标准的k-e模型。在所有情况下，只有标准k-e模型结果与两种情况下的数据趋势都匹配。可以说，在高FST和高M的情况下，所有模型都无法很好地预测数据。结论是，这些偏差是由高FST和高M引起的。在高M下，在注入孔附近，偏差可能是由Boussinesq假设的局限性引起的，该假设将雷诺应力的方向与平均应变率相关。同样，似乎所有模型都存在麻烦，包括由于无法考虑自由流中湍流的高扩散程度而导致的高FST效应。

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