凹槽叶顶椭圆与圆形冷却孔轴向偏转角对气热特性的影响研究

Effects of Axial Inclination Angle of Oval and Round Cooling Holes on Aero-Thermal Performance of a Squealer Tip

关键词:  燃气轮机  气膜冷却  凹槽叶顶  吹风比  椭圆孔

Key words:  Gas turbine  Film cooling  Squealer tip  Blowing ratio  Oval hole

摘要:

改善叶顶气热特性对提升透平的气动效率和安全可靠性具有重要意义。本文引入了一种在冷却方面具有重大潜力但在叶顶研究中鲜有报道的冷却孔型——椭圆孔，并采用ANSYS CFX 19.2商业软件求解三维稳态RANS方程组，通过数值模拟方法分析了凹槽叶顶椭圆孔与圆形孔在气热特性方面的差异，以及轴向偏转角结构对叶顶流场、冷却与传热的影响。研究发现，正轴向偏转结构减小了气膜抬升与分离，有利于提高平均冷却效率并降低泄漏流量与总压损失，负偏转结构虽然提高了气膜覆盖面积但大大增大了射流涡尺度，导致了泄漏流量与总压损失的增加。椭圆孔相比圆形孔其出流边曲率更小，气膜覆盖范围更宽，在大偏转角结构减弱了出流收缩现象，能显著提升气膜冷却效率与减小射流涡尺度，但在小偏转角结构中易产生流动分离导致射流涡尺度的增长。本文还发现凹槽前缘负偏角冷却孔在吹风比M=2.0时能有效减弱凹槽前缘再附区换热恶化现象并显著提升气膜覆盖范围，其中OH-60结构的平均气膜冷却效率达到了0.1111，是吹风比M=1.0时参考结构的9.320倍。

Abstract:

It is of great significance to the aerodynamic and reliability development of gas turbine to improve the aero-thermal performance on the blade tip. The oval cooling hole is introduced in this paper， which is of sufficient potential in film cooling but rarely used in the study of blade tip. The ANSYS ICEM 19.2 commercial software is used to solve the three-dimensional steady RANS equations. The differences of aero-thermal performance between oval holes and round holes on a squealer tip are studied by the numerical simulation， and the effects of axial inclination angle on the flow field and cooling and heat transfer on the blade tip are also investigated. It is found that the positive axial inclination structure has limited the film lift-off， improving the average cooling effectiveness and reducing the leakage flow and total pressure loss. Although the negative inclination structure has improved the film coverage， it greatly develops the scale of jet vortex， resulting in the increase of leakage flow and total pressure loss. Compared with round holes， oval holes provide smaller outlet edge curvature and wider film coverage， weakening the outflow contraction， significantly improving the film cooling effectiveness and reducing the jet vortex scale in the structure with large inclination angle. However， it is easy to generate flow separation in the structure with small inclination angle， resulting in the increase of jet vortex scale. It is also found that the jets at the front of the cavity with negative inclination angle can effectively weaken the deterioration of heat transfer in the area of cavity vortex reattachment and significantly improve the film coverage at the blowing ratio of 2.0. The highest average film cooling effectiveness is obtained by OH-60 with 0.1111， which is 9.320 times that of the reference structure at blowing ratio 1.0.