上游横向间断肋布置方式对气膜冷却性能的影响

Effect of Arrangement for Upstream Divided Ramps on Film Cooling Performance

为了采用气膜冷却来保护燃气轮机叶片免受高温侵蚀,针对进一步提高气膜冷却效率、减少冷却空气消耗量的需求,提出了带有上游间断肋的气膜冷却结构。采用k-ε湍流模型数值研究了带有上游横向肋结构的气膜冷却性能,分析了横向无间断肋、两侧间断肋、间断数段肋和中间间断肋这4种上游不同横向肋布置方式对气膜冷却流动的影响,比较了4种结构的气膜冷却效率和换热系数。结果表明:横向肋对下游冷气的卷吸能力与肋片长度有关,与肋片的布置方式无关;不同肋片布置方式会产生不同的涡结构,即中心间断肋会诱导主流产生一个与肾形涡旋转方向相反的涡对,从而增加冷却射流的展向扩散,有利于提高下游气膜冷却性能,而两端间断肋会诱导主流产生一个与肾形涡旋转方向相同的涡对,该涡对会进一步抬离冷却射流,降低下游气膜冷却性能;在气膜孔上游布置中心间断肋能提供最高的展向平均绝热气膜冷却效率和实际热降值。

To protect the gas turbine blades suffering from the hot gas by adapting the film cooling technology,a novel film cooling geometry with an upstream ramp is proposed in view of the requirement for further increasing adiabatic film cooling effectiveness and decreasing expense of coolant.The performance of film cooling with upstream ramps is numerically investigated with k-εturbulence model.The effects of arrangement for four different ramps,including the undivided ramp,the ramp divided in the lateral sides,the ramp divided in several positions and the ramp divided in the center,on flow structures are analyzed.The adiabatic film cooling effectiveness and heat transfer coefficient of these four film cooling geometries are compared.The results show that the intensity of entrainment is sensitive to the length of ramp and is independent on the ramp arrangements. Different vortex structures are induced due to the different arrangement for ramps.The ramp divided in the center region generates a pair of vortexes which rotates in the opposite direction with the kidney vortexes,and this pair of vortexes contributes to the lateral spreading of coolant,which increases the film cooling performance.The ramp divided on both sides generates a pair of vortexes which rotates in the same direction with the kidneyvortexes,and this pair of vortexes lifts off the coolant further,which increases the film cooling performance.The highest adiabatic film cooling effectiveness in the spanwise direction and the highest NHFR（net heat flux reduction）are observed in the case of the ramp divided in the center.