叶型表面曲率对离散孔气膜冷却性能的影响

由于型面曲率的影响,涡轮叶片前缘和吸力面的冷却气膜易于脱离型面,气膜冷却效果下降。本研究将叶片型线分段拟合,建立了多个单一曲率的曲面模型(R/D=-30、-75、120、∞),研究涡轮叶片表面曲率对于气膜冷却的影响。流动与传热的数值模拟采用Fluent软件,湍流模型选择RNGk-ε模型,模拟方法经平板流动进行的结果验证是可靠的。在不同吹风比(M=0.5、1.2、2.0)条件下,计算比较了不同曲率曲面上气膜单孔下游的壁面传热系数以及局部平均气膜冷却效率。结果表明:涡轮叶片型面曲率对气膜冷却效果的影响与吹风比有关。不同曲率的型线部分,应该设计采用不同的吹风比,气膜冷却效果可能取得最佳。低吹风比M<1时,凹面曲率对气膜换热系数是强化,凸面基本没有作用。高吹风比M>1时,曲率不影响换热能力,冷却效果则取决与气膜相对于型面的流动状态和与主流的掺混能力。

Influence of the Surface Curvature of a Blade Profile on Its Discrete Hole Air-film Cooling Performance

Due to the influence of the profile surface curvature of a turbine blade,the cooling air film at its leading edge and on its suction surface is liable to be separated from its profile surface and the air film cooling effectiveness decreases.A fitting of the blade profile was made in several sections and several curved surface models(R/D=-30,-75,120,∞) for a single curvature were established.The influence of the blade surface curvatures on the air-film cooling performance was studied.The commercial software Fluent was used to numerically simulate the flow and heat transfer.The RNG k-ε turbulent model was chosen.It has been verified by the results of a flat-plate flow that the simulation method is reliable.At various blow ratios(M=0.5,1.2,2.0),the wall surface heat transfer coefficients and local average air film cooling efficiencies of different curved surfaces at the downreaches of a single air film hole were calculated and compared.The research results show that the influence of the turbine blade profile curvatures on the air film cooling effectiveness is dependent on the blow ratios.For any blade profile section with a different curvature,a different blow ratio should be adopted in design and in such a case,the optimum air film cooling effectiveness can be possibly achieved.When M<1,a concaved surface curvature can enhance the air film heat transfer coefficient while a convexed surface curvature basically plays no role.When M>1,the curvature will not influence the heat exchange capacity while the cooling effectiveness will depend on the flow status of the air film relative to the blade profile and the mixing and dilution capacity with the main stream.