Influence of axially-convergent contouring on cascade endwall film cooling characteristics in gas turbine
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摘要: 为有效评估轴向收敛造型对端壁气膜冷却性能的影响，数值研究了不同吹风比下，轴向收敛造型对跨声速燃气涡轮叶栅端壁上游双排离散孔绝热气膜冷却效率的影响。模拟某工业燃气涡轮真实运行工况（进口湍流度为16%、出口马赫数为0.85、出口雷诺数为1.5×106），采用基于“两类热边界条件”模型的壁面传热系数和绝热冷却效率数值预测方法，比较分析了3种吹风比（1.0、2.5、3.5）下，简化平板端壁结构和轴向收敛造型端壁结构的端壁热负荷分布、绝热气膜冷却效率分布和近端壁二次流场结构，以及端壁上游气膜孔射流对叶片表面的二次冷却作用（幻影冷却）。结果表明：轴向收敛造型可以削弱马蹄涡强度，降低端壁热负荷，尤其是叶片肩部区域；轴向收敛造型可以显著增加端壁气膜覆盖范围和绝热气膜冷却效率，尤其在叶片前缘和压力面等难以冷却区域；随吹风比增加，轴向收敛造型对端壁气膜冷却特性的影响效果先增加后减小，在设计吹风比为2.5时，轴向收敛造型对端壁绝热气膜冷却效率的增强效果最显著（增加约35%）；轴向收敛造型显著增加叶片前缘和压力面幻影冷却面积，尤其是叶片前缘附近面积增加约100%（设计吹风比下，冷却区域达0.1倍叶高），可有效减小叶片冷却的冷气需求流量。轴对称收敛端壁造型是进一步提高燃气涡轮叶栅端壁绝热气膜冷却效率、减小冷气流量，实现端壁高效冷却布局的有效技术途径。Abstract: In order to evaluate the influences of the axially-convergent contouring on the endwall film cooling performance of the upstream double-row film holes，the cascade endwall adiabatic film cooling effectiveness was predicted through numerical simulation.The endwall thermal load distribution，adiabatic film cooling effectiveness distribution and secondary flow field were calculated and analyzed for two endwall configurations （flat endwall and axially convergent contoured endwall） at three different blowing ratios （1.0，2.5，3.5） under the simulated realistic operation condition of an industrial gas turbine，inlet turbulence of 16%，exit Mach number of 0.85，exit Reynolds number of 1.5×106，based on “two types of thermal boundaries” numerical method.Simultaneously，the secondary cooling （phantom cooling） phenomenon of the upstream purge flow on the vane surface was noticed.Results showed that compared with the flat end-wall configuration，the axially-convergent contoured endwall reduced the strength of the horse-shoe vortex and endwall thermal load，especially at the region of vane suction surface shoulder.For the axially-convergent contoured endwall，the upstream coolant jets were more efficiently targeted at the endwall，yielding higher endwall adiabatic film cooling effectiveness，especially at the regions of the vane leading edge and vane pressure side where cooling was harder due to the stronger secondary flow.At the increasing blowing ratio，the effects of axially-convergent contouring on endwall film cooling first increased and then decreased.The axially-convergent contouring resulted in a significant increase （up to 35%） in end-wall adiabatic film cooling effectiveness at design blowing ratio of 2.5.The axially-convergent contouring obviously increased the phantom cooling size around the vane leading edge and pressure surface，especially at the region around the vane leading edge （up to 100%，0.1 span at design blowing ratio）.This led to an obvious reduction in the demand of coolant.Therefore，the axially-convergent contoured endwall is an effective approach to increase the endwall adiabatic film cooling effectiveness，reduce the demand of coolant and realize the efficient endwall cooling scheme.
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Key words:
- axially-convergent contouring /
- cascade endwall /
- blowing ratio /
- film cooling /
- phantom cooling
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