Trailing-Edge Cooling for Gas Turbines
Trailing-Edge Cooling for Gas Turbines
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DOI：
10.2514/1.20898
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发表时间：
2006-03
影响因子：
1.9
通讯作者：
F. J. Cunha;M. Chyu
中科院分区：
文献类型：
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作者：
F. J. Cunha;M. Chyu
现代高压涡轮机翼型的后缘部分是从涡轮机性能和耐久性观点来看需要高度关注的区域。后缘附近的气动损失包括膨胀波、正激波和尾流脱落。与后缘相关的热问题也非常复杂和具有挑战性。为了保持有效的冷却，确保金属温度低于设计极限是特别困难的，因为它需要在翼型件的相对小的区域中实施。迄今为止，很少有人致力于推进翼型后缘区域热特性的基本理解。本文介绍了四种最具代表性的后缘构型的温度分布的封闭形式的解析解。所研究的结构形式有：1）无泄放的实心楔形，2）带狭缝泄放的楔形，3）带离散孔泄放的楔形，4）带压力侧削减狭缝泄放的楔形。这四种情况之间的比较主要是在翼型金属温度和由此产生的冷却效果的背景下。本文进一步讨论了优选后缘冷却配置的总体和详细设计参数，因为它们影响涡轮机翼型性能和耐久性。本文还介绍了当前对后缘构型传热的实验研究。后缘前有一个基座阵列的内部冷却通道。基座阵列由圆形针翅和椭圆形特征或出口泪滴组成。在基座阵列的下游，后缘在由椭圆形泪滴分隔的压力侧缩减中退出。在整个湿表面的内部冷却室的局部传热系数已被确定使用“混合”测量技术的基础上瞬态液晶成像。混合技术采用瞬态导热模型在一个半无限的固体解决端壁表面上的传热系数由绝热层。在假设低毕奥数的情况下，用集总电容法求解了基座上的传热系数。与热发展光滑通道的情况相比，组合的壁和端壁的总传热显示出显着的增强。在吸入侧的最下游区段附近，由压力侧削减引起的平台暴露于与热气体和排出的冷却剂混合的流。利用这种混合液晶技术，对陆面段的绝热效率和传热系数进行了表征。库尼亚博士是普惠公司的首席工程师，负责商用和军用发动机项目的先进涡轮机设计。库尼亚博士还负责为一个大学联盟制定技术方向，并负责在最先进的冷却技术领域的内部研究项目，该技术适用于极端苛刻的燃气涡轮机转子入口温度。库尼亚博士的职业生涯跨越了27年的涡轮机原始设备制造商，包括通用电气和西门子。库尼亚博士撰写了许多技术论文和燃气涡轮机设计标准。库尼亚博士拥有21项美国专利，目前是IGTI-ASME传热委员会的成员。
The trailing-edge section of modern high-pressure turbine airfoils is an area that requires a high degree of attention from turbine performance and durability standpoints. Aerodynamic loss near the trailing edge includes expansion waves, normal shocks, and wake shedding. Thermal issues associated with trailing edge are also very complex and challenging. To maintain effective cooling ensuring metal temperature below design limit is particularly difficult, as it needs to be implemented in a relatively small area of the airfoil. To date, little effort has been devoted to advancing the fundamental understanding of the thermal characteristics in airfoil trailing-edge regions. Described in this paper are the procedures leading to closed-form, analytical solutions for temperature profile for four most representative trailing-edge configurations. The configurations studied are 1) solid wedge shape without discharge, 2) wedge with slot discharge, 3) wedge with discrete-hole discharge, and 4) wedge with pressure-side cutback slot discharge. Comparison among these four cases is made primarily in the context of airfoil metal temperature and resulting cooling effectiveness. Further discussed in the paper are the overall and detail design parameters for preferred trailing-edge cooling configurations as they affect turbine airfoil performance and durability. Also described in this treatment is a current experimental investigation of heat transfer over a trailing-edge configuration. The trailing edge is preceded with an internal cooling channel of pedestal array. The pedestal array consists of both circular pin fins and oblong shaped features or exit teardrops. Downstream to the pedestal array, the trailing edge exits in a pressure side cutback partitioned by the oblong-shaped teardrops. The local heat-transfer coefficient over the entire wetted surface in the internal cooling chamber has been determined using a “hybrid” measurement technique based on transient liquid crystal imaging. The hybrid technique employs the transient conduction model in a semi-infinite solid for resolving the heat-transfer coefficient on the end-wall surface uncovered by the pedestals. The heat-transfer coefficient over a pedestal can be resolved by the lumped capacitance method with an assumption of low Biot number. The overall heat transfer for both the pedestals and end-walls combined shows a significant enhancement compared to the case with thermally developed smooth channel. Near the most downstream section of the suction side, the land, caused by pressure side cutback, is exposed to the stream mixed with hot gas and discharged coolant. Both the adiabatic effectiveness and heat-transfer coefficient on the land section are characterized by using this hybrid liquid-crystal technique. Dr. Cunha is a Principal Engineer at Pratt & Whitney responsible for advanced turbine designs of commercial and military engine programs. Dr. Cunha is also responsible for establishing technical direction for a consortium of Universities as well as in-house research programs in the area of state-of-the-art cooling technologies suitable for use with extremely aggressive gas turbine rotor inlet temperatures. Dr. Cunha’s professional career spans a period of 27 years with turbine original equipment manufacturers including General Electric and Siemens. Dr. Cunha has authored numerous technical papers and gas turbine design standards. Dr. Cunha holds 21 U.S. patents in turbomachinery and is presently a member of the IGTI-ASME heat transfer committee.