Numerical Analysis of Tip Leakage Flow in Steam Turbine Rotor Cascades

In order to investigate the effects of shroud on the tip leakage flow in turbine rotor cascades, numerical simulations on different tip clearance leakage flow of unshrouded and shrouded blade in the stage of a steam turbine are performed, the κ-ω sst turbulence model and the structure grid are adopted. The formation and development of tip clearance leakage flow and leakage vortex, as well as their influences on turbine performance are analyzed.The results show that, for the unshrouded rotor cascades, the clockwise leakage vortex is formed near the suction side and trailing edge because of the blade tip leakage flow exiting, and the incidence of the leakage vortex becomes larger from upstream to downstream of the blade. While for the shrouded rotor cascades, the counterclockwise leakage vortex is formed on the top of blade trailing edge. However, the rotation directions of their corresponding passage vortex are both opposite from that of leakage vortex. The intensity of leakage vortex and the total pressure loss coefficients increase with increasing the tip clearances. When the tip clearance is the same, the total pressure loss coefficients of the shrouded blade is always less than that of the unshrouded blade in an appropriate position at the blade tip above 80 percent blade height.