扇形和圆形气膜冷却直孔的流场和传热实验研究

Experimental Study of Film Cooling Effectiveness of a Single Fan-Shaped Hole with Streamwise Angle of 90°

对锥顶角（扇形角）γ分别为１５°和３０°的垂直扇形气膜冷却单孔射流下游的流场和传热进行了详细的实验研究，并与相同实验条件下圆孔射流的情形进行了比较。结果发现，扇形喷口下游的速度边界层等值线具有两种基本的分布形态，即使在高吹风比Ｍ＝２．０时，扇形孔的下游也没有明显大于主流速度的射流区域出现。吹风比Ｍ≥１．０时喷孔两侧边缘处沿流向形成了一对转向相反、强度较弱的纵向耦合涡。在相同的吹风比下，扇形喷孔出口面积的增大能够有效地降低耦合涡的强度和Ｖ、Ｗ速度分量，从而提高了气膜冷却效率，尤其是提高了喷孔两侧下游位置上的冷却效率。在喷孔中线下游位置上，当吹风比Ｍ＝０．３时，扇形角γ的变化对冷却效率几乎无影响，而当吹风比Ｍ≥１．０时，扇形喷孔较圆孔的冷却效率明显高得多。在喷孔中线两侧ｚ／Ｄ＝１．３的位置上，当扇形角相同时，吹风比低的射流冷却效率较高；当吹风比相同时，扇形角γ＝１５°和３０°的冷却效率非常接近。

Since 1994, we have been exploring the effect of hole shape on its film cooling effectiveness as a part of a project supported by Rolls-Royce plc, London, U.K. After studying mechanism of interaction between mainstream and jet in a previous paper , we now present our experimental data on the flow and heat transfer downstream of a single fan-shaped hole with streamwise angle of 90°. Fig.1 shows the difference of fan-shaped hole from conventional circular hole; as γ increases, the fan flare becomes larger. In our experiments, we took γ to be 15° and 30°. We knew from our mechanism study that a pair of counterrotating vortices exist. In Fig.3, only one half of the pair of counterrotating vortices is shown, as we could take advantage of symmetry. With increasing γ (flare angle), for blowing ratio M ≥1.0, the strength of the weak vortices decreases significantly as can be seen in Fig.5, and film cooling effectiveness increases significantly as can be seen in Fig.7. For M =0.3, fan flare has almost no effect on improving film cooling effectiveness.