吹风比和肋板对叶片尾缘开缝气膜冷却特性的影响

Effects of Blowing Ratio and Land Extension on Blade Trailing Edge Cutback Film Cooling Effectiveness

为了阐明吹风比和肋板对燃气透平叶片尾缘开缝区域气膜冷却性能的影响,采用延迟-分离涡模拟方法求解了尾缘开缝模型的流量系数、非定常流场结构和气膜冷却效率,采用实验数据考核了延迟-分离涡模拟方法对流量系数和气膜冷却效率预测的有效性,获得了使尾缘开缝壁面气膜冷却效率最佳吹风比。结果表明:流量系数随吹风比增加而增大,但吹风比大于0.65后,流量系数几乎不受吹风比影响;在吹风比0.20~0.65范围内,尾缘开缝壁面气膜冷却效率随吹风比增加而增加;在吹风比0.80~1.25范围内,冷热气掺混剧烈,冷却效率略微下降;肋板结构增加了冷气通道的阻塞效应,并限制了开缝区域冷气旋涡的发展,导致展向涡提前扭曲、变形和分解;相对于无肋板结构,带肋尾缘开缝结构的流量系数下降了约5%,气膜冷却性能提升了约10.8%。开缝下游的旋涡脱落和冷热气流间的掺混是影响开缝壁面冷却效率的主要原因,综合考虑冷气消耗和气膜冷却效率,无肋板时最佳吹风比为0.65,带肋板时最佳吹风比为0.5。

To investigate the effects of blowing ratio and land extensions on the film cooling performance of a gas turbine blade trailing edge cutback,the delayed-detached eddy simulation(DDES)is utilized to compute the discharge coefficient,transient flow structures,and film cooling effectiveness of a trailing edge cutback model,and the experimental data is adopted to validate the reliability of DDES for the discharge coefficient and film cooling effectiveness predictions.As a result,the study determined the optimum blowing ratio for ensuring the film cooling effect at the trailing edge cutback.The findings show that the discharge coefficient rises in correspondence with an increase in the blowing ratio.However,once the blowing ratio surpasses 0.65,its impact on the discharge coefficient diminishes significantly.For the blowing ratio ranging from 0.20 to 0.65,the film cooling effectiveness at the trailing edge cutback improves with an increase in the blowing ratio.As the blowing ratio increases from 0.80 to 1.25,interactions between the coolant and hot mainstream are intensified,resulting in a slight reduction in the cooling effect.The existence of land extensions amplifies the blockage of cooling slot and inhibits the development of coolant vortices in the trailing edge cutback region,leading to premature twisting,distortion,and fragmentation of the transverse vortex system.Compared to the trailing edge cutback without land extensions,the discharge coefficient for the configuration with land extensions decreases by about 5%while the film cooling effectiveness increases by about 10.8%.The vortex shedding downstream the cooling slot and interactions between coolant and hot mainstream are the main reasons affecting the cooling effect at the trailing edge cutback.Considering both coolant consumption and film cooling effectiveness,the optimal blowing ratio for the trailing edge cutback without land extensions is identified as 0.65.Contrastingly,for the trailing edge cutback with land extensions,the preferred blowing ratio stands at 0.5.