汽轮机末级动叶片出口边水蚀特性及疲劳裂纹扩展的研究

空冷汽轮机组、调峰汽轮机组及热电联产汽轮机低压缸在小容积流量工况下运行时，末级动叶片根部分离流区的回流会将排汽缸湿蒸汽中的水滴带回叶栅通道，使动叶片吸力面出口区侵蚀并引发疲劳裂纹。为了确定机组负荷工况对叶片水蚀特性及叶片安全性的影响，首先利用流线曲率法发展出一种计算回流气动特性及水滴撞击叶片速度的方法。并用以分析了一台200MW汽轮机末级动叶根部出口边水蚀的特性，分析结果与实际情况较一致。此后，采用断裂力学理论研究了出口边水蚀缺口处的裂纹萌生期与扩展的增长率，计算结果与实际裂纹发展情况较为符合。所发展的方法为研究预防叶片出口边水蚀方法和合理制定机组检修周期提供了有用手段。

Study of Water-erosion Characteristics and Fatigue Crack Propagation of Last Stage Moving Blade Trailing Edge of a Steam Turbine

In air-cooled steam turbine, peak regulating steam turbine and the low pressure part of cogeneration unit operating under low volume flow conditions, the reverse flow in hub region of last rotor blade will carry water drops of wet steam in exhaust hood back to moving cascade passage, and cause moving blade trailing edge erosion and in turn fatigue crack. In order to understand the effects of load conditions on blade erosion and blade life, an approach for analyzing reverse flow characteristics and the impact velocity of water drops impinging on the blade surface is developed by using streamline curvature method, and then the water-erosion characteristics of a 200MW steam turbine last stage blade are analyzed. The computed results are consistent with actual circumstances. Furthermore, the crack initiation period and crack-growth rate are computed according to the principles of fatigue fracture mechanics, and the obtained results accord with real instance. The developed approach can be used to investigate the method for preventing blade erosion and to determine the reasonable maintenance interval.