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Discussions of some myths and concerned practices of film cooling research

机译：讨论电影冷却研究的一些神话和相关实践

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This paper focuses on discussing four myths and concerned conventional practices of film cooling research guided by a series of computational simulations. The issues that have been discussed include: (a) the film cooling effectiveness () is given a constant (0.6) to calculate the heat flux ratio (HFR = q"/q_0") between film-cooled and no-film cases; (b) the adiabatic wall temperature is the driving temperature of film cooling; (c) the adiabatic film heat transfer coefficient can be obtained from an isoenergetic film experiment (T_j = T-g); (d) using a heated surface can provide a simplified approach to simulate the film-cooling condition. The result shows that the adiabatic wall temperature is not always the driving temperature (i.e. T_(aw) is not always larger than T_w), but T_(aw) does act well as the reference temperature in correctly predicting the heat flux direction and giving an always positive adiabatic film heat transfer coefficient. Using a constant value for φ is questionable and may lead to un-realistic or false HFR. The conventional equation of HFR was not theoretically exact and can lead to an error of up to 20%. A revised HFR equation is provided in this paper. The dominant energy passage in turbine airfoil film cooling is always from hot combustion gas flows into the airfoil; therefore, employing a heated wall as a boundary condition with hotter main stream flow and cold film injection to simulate the actual film cooling condition is found to be fundamentally questionable. A conjugate simulation that includes wall heat transfer and internal flow cooling shows that reversed heat transfer from blade to gas that gives a negative HFR is possible, due to the heat conduction from the downstream hotter region into the near film hole cooler region.
机译：本文将重点讨论四个神话，并在一系列计算模拟的指导下进行有关薄膜冷却研究的常规实践。已讨论的问题包括：（a）薄膜冷却效率（）赋予常数（0.6），以计算薄膜冷却和无薄膜情况之间的热通量比（HFR = q“ / q_0”） ; （b）绝热壁温度是薄膜冷却的驱动温度； （c）绝热膜的传热系数可通过等能膜实验获得（T_j = T-g）； （d）使用加热的表面可以提供简化的方法来模拟薄膜冷却条件。结果表明，绝热壁温并不总是驱动温度（即T_（aw）并不总是大于T_w），但是T_（aw）在正确地预测热通量方向并给出绝热膜的传热系数始终为正。将恒定值用于φ是有问题的，并且可能导致不切实际或错误的HFR。 HFR的常规公式在理论上并不精确，并且可能导致高达20％的误差。本文提供了修订的HFR方程。涡轮机翼型膜冷却中的主要能量通道始终来自热的燃烧气体流入翼型。因此，发现采用加热壁作为主流条件，并采用较热的主流和冷膜注入来模拟实际的膜冷却条件是根本有问题的。包括壁面传热和内部流动冷却的共轭模拟表明，由于从下游较热区域到近膜孔较冷区域的热传导，从叶片到气体的反向传热是可能的，从而产生负HFR。

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