Effective design of film cooled engine components requires the ability to predict behavior at engine conditions. This is commonly accomplished through low temperature testing on scaled up geometries. The adiabatic effectiveness, η, is one indicator of the performance of a film cooling scheme. Performing an experiment to measure rj in a low temperature wind tunnel requires appropriate selection of the coolant flow rate. Perhaps the most common flow rate parameter that is used to characterize the coolant flow relative to the freestream is the mass flux ratio, or blowing ratio, M. This is usually used in lieu of the velocity ratio to account for the fact that the density of the coolant is typically much larger than that of the hot freestream gas. Numerous studies have taken place evaluating the ability of M to properly scale the effects of density ratio and its performance has produced mixed results. The momentum flux ratio, I, is an alternative that is also found to have mixed success, leading some to recommend matching the density ratio to allow simultaneous matching of M and I. Nevertheless, widely varying results in the literature regarding the efficacy of these coolant flow rate parameters to scale the density ratio suggests there may be other largely ignored effects playing a role in the thermal physics. In the present work, thermal experiments were performed to measure adiabatic effectiveness on a flat plate with a single 7-7-7 shaped hole. Various coolant gases were used to give a large range of thermodynamic property variations. It is shown that a relatively new coolant flow rate parameter that accounts for not only density variations but also specific heat variations, the advective capacity ratio (ACR), far exceeds the ability of either M or I to provide matched adiabatic effectiveness between the various coolant gases that exhibit extreme property differences. Particularly considering that the specific heat of the coolant in an engine is significantly lower than the specific heat of the freestream gas, ACR is shown to be appropriate for characterizing non-separating coolant flow situations.
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机译：薄膜冷却发动机部件的有效设计需要能够在发动机条件下预测行为。这通常是通过对缩放的几何形状的低温测试来实现的。绝热有效性η是薄膜冷却方案性能的一个指标。 Performing an experiment to measure rj in a low temperature wind tunnel requires appropriate selection of the coolant flow rate.也许这是用于将相对于自由流的冷却剂流表征最常见的流量参数是质量流量比或吹塑比，M.这通常是代替速度比的用于帐户的事实的密度冷却剂通常比热自由流气体的气体大得多。已经进行了许多研究评估了M以适当地缩放密度比的影响，并且其性能产生了混合结果。电量磁通比I，也是一种替代方案，也被发现具有混合成功，导致一些建议匹配密度比以允许M和I的同时匹配。然而，关于这些冷却剂的功效的文献中的显着变化导致的结果流量参数缩放密度比表明可能存在其他大量忽略在热物理中发挥作用的影响。在本作工作中，进行热实验以测量具有单个7-7-7个形状的孔的平板上的绝热效果。各种冷却气体用于提供大量的热力学性质变化。结果表明，一种相对较新的冷却剂流速参数，其不仅占密度变化，而且还具有特定的热变化，平均的容量比（ACR），远远超过M或I在各种冷却剂之间提供匹配的绝热效果的能力展示极端性质差异的气体。特别是考虑到在发动机的冷却水的比热是显著低于自由流气体的比热，ACR被示为适当的用于表征非分离的冷却剂流的情况。
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