Numerical Study of the Secondary Flow in Steam Turbine Static Cascade under Varying Conditions

Based on finite element volume method and fully implicit multi-grid coupling algorithm, with a certain distortion degree of the static cascade flow field is solved in three-dimensional steady-state under subcritical, critical and supercritical flow state. The paper analyses and calculates the developmental characteristics of the secondary flow in the lower wall of the cascade channels and the aerodynamic characteristic of the cascade. The calculated results under different critical state show that the secondary flow loss of cascade end wall is bound up with cascade profile and the upper and lower endwall. Especially in the supercritical flow state, there are strong disturbances of steam flow in the cascade ends and cascade shape surface. Meanwhile, the calculated results reveal the characteristic of vortices evolution in cascade channels and also shows that the strength of secondary flow develops rapidly. Two obvious vortex areas form at the nearby of the cascade back-arc of the upper and lower endwall. The development of vortices under subcritical flow state is similar to the development of vortices under critical flow state. The passage vortex moves backward under supercritical flow state. Vortex phenomenon caused by steam flow is separated from side wall near outlet of cascade back-arc. And steam flow deflects at the same time.