不同激励形式对脉动气膜冷却特性影响的数值研究

Numerical Study on Effects of Different Excitation Forms on Forced Film Cooling Characteristics

关键词:  非定常数值模拟  脉动气膜冷却  方波  正弦波  冷却效率  主流入侵  连续性

Key words:  Unsteady numerical simulation  Forced film cooling  Square wave  Sinusoidal wave  Cooling effectiveness  Ingestion of crossflow  Continuity

摘要:

为了探究不同激励形式对脉动气膜冷却特性的影响，在35°倾角平板射流模型中，采用非定常数值模拟方法进行相关研究。挑选常用的方波和正弦波作为冷气激励，无量纲激励频率斯特劳哈尔数St=0.019,0.047,0.093,0.263,0.441，重点对冷气附着和高温主流入侵现象进行了对比研究。结果表明：正弦激励下的冷气对壁面有更强的附着和更高的冷却效率；方波激励下的冷气穿透能力较强但对壁面附着相对较弱。此外，方波激励下存在主流入侵，会烧蚀气膜孔及局部壁面；而正弦激励使得冷气连续变化，能明显抑制主流入侵。更进一步，提高脉动周期内的最低吹风比不是抑制主流入侵的最佳方式，因为主流入侵主要是因为冷气量变化过于剧烈。针对正弦激励，冷气的无量纲激励频率St>0.263后也会导致主流入侵。考虑冷却效果和避免主流入侵，建议在实际应用中选用较低频连续波形作为激励。

Abstract:

In order to study the effects of different excitation forms on forced film cooling characteristics, relevant investigation was performed in a 35° inclined jet-in-crossflow model by unsteady numerical simulation method. The commonly used waves, square wave and sinusoidal wave were selected as excitations to the coolant and the nondimensional forcing frequencies of Strouhal numbers are 0.019, 0.047, 0.093, 0.263 and 0.441. This paper mainly compared the attachment of the coolant as well as the ingestion of the hot mainstream. The results show that coolant with sinusoidal excitation has stronger attachment to the wall and higher cooling effectiveness, whereas coolant with square excitations has stronger penetration but relatively weaker attachment. Besides, ingestion of hot mainstream exists under square excitation, which can cause ablation to the holes and parts of the wall. However, sinusoidal excitation makes the coolant change gradually, which significantly restrains the ingestion. Further, improving the lowest blowing ratio is not the best way to restrain the ingestion, since the ingestion is mainly caused by the excessively changed amount of coolant. As for sinusoidal excitation, the coolant with Strouhal numbers higher than 0.263 also results in the ingestion of mainstream. Considering cooling effectiveness and restraining ingestion, continuous wave with relatively low frequency is recommended for practical use.