To increase cooling effectiveness, film-hole designs with serrated trenches have been widely reported in the gas turbine industry. However, the unsteadiness level of the film coverage and the inevitable environmental pulsation are always neglected, which may lead to an unexpected failure of hot components by the instantaneous exposure to a high-temperature environment. In this work, a series of large eddy simulations are conducted to comprehensively evaluate the transient film cooling performance with serrated trench designs, and the effect of pulsed cooling air injection is discussed. Time-averaged results reveal that: 1) under steady condition, serrated trench design exhibits a higher film effectiveness in most regions compared to the traditional transverse trench, which supports the previously reported advantage. 2) Pulsed cooling air injection would cause a significant reduction of film effectiveness for the serrated trenches. Under the pulsed condition, film effectiveness with a serrated angle of 100° can be over 20% lower than that with a traditional transverse trench. Moreover, transient results indicate that under both steady and pulsed conditions, the serrated trenches always exhibit a lower steadiness level of film cooling, relative to the traditional transverse trench. Therefore, it should be prudent to suggest film cooling with serrated trenches in practical designs.

中文翻译：

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脉冲冷却剂喷射对锯齿状沟槽设计非稳态气膜冷却特性的影响

为了提高冷却效率，燃气轮机行业广泛报道了带有锯齿状沟槽的膜孔设计。然而，薄膜覆盖的不稳定程度和不可避免的环境脉动总是被忽视，这可能会导致热部件因瞬时暴露于高温环境而发生意外故障。在这项工作中，进行了一系列大涡模拟，以综合评估锯齿状沟槽设计的瞬态气膜冷却性能，并讨论了脉冲冷却空气喷射的效果。时间平均结果表明：1）在稳定条件下，与传统横向沟槽相比，锯齿状沟槽设计在大多数区域表现出更高的薄膜有效性，这支持了之前报道的优势。 2) 脉冲冷却空气喷射会导致锯齿状沟槽的薄膜有效性显着降低。在脉冲条件下，锯齿角为100°的薄膜效率可比传统横向沟槽的薄膜效率降低20%以上。此外，瞬态结果表明，在稳定和脉冲条件下，相对于传统的横向沟槽，锯齿状沟槽始终表现出较低的薄膜冷却稳定性水平。因此，在实际设计中应谨慎建议采用锯齿状沟槽进行薄膜冷却。