汽轮机动叶顶部间隙泄漏流动特性的数值模拟

以一个小展弦比轴流透平级为研究对象,采用数值方法对不同动叶顶部间隙情况下的间隙泄漏流动进行了分析,研究了间隙流和间隙涡的形成、发展及其对透平级性能的影响.以三维流线和极限流线为手段,分析了6种间隙尺寸下动叶顶部的泄漏流和泄漏涡造成的损失及其与主流掺混的过程.结果表明:动叶顶部间隙两侧压力面和吸力面之间的压力差使汽流从压力面被吸入间隙,跨过叶顶,进入相邻叶栅通道的吸力面,导致泄漏流动;与无间隙的情况相比,叶顶间隙的存在使上端壁处的流场发生明显变化,引起损失迅速增长;随着间隙的增大,泄漏涡的产生位置提前,强度增大,从而导致更大的流动损失.

Numerical Simulation of the Aerodynamic Characteristics of Blade Tip Leakage Flow in Steam Turbines

Leakage flows,at tips of blades with differently sized clearances,are being analyzed,for an axial flow turbine with stages of low aspect ratio.The formation and development of clearance flow and clearance vortices were studied, as well as their influence on the properties of turbine stages.Via 3-dimensional streamlines,as well as limit streamlines,the leakage through 6 differently sized tip clearance,the consequently caused losses,as well as the process of its mixing with the main flow,were analyzed.Study results indicate that it is the pressure difference,befween the pressure and the suction surface at blade tip,that causes steam to be sucked from the pressure surface into clearance and thereupon,after traversing blade tip,to cover the cascade's neighbouring flow passage's suction surface;thus initiating the leakage flow.In contrast with cases without clearances,blade tip clearance affects noticeable changes in the flow field,strvcture adjoining the upper wall,causing losses to increase rapidly. With increasing clearance,leakage vorties appear at an earlier location,and also with stronger intensity,causing consequently fluid losses to increase.