| dc.description.abstract | In an axial flow turbine, the tip leakage flow leads to considerable tip leakage loss and causes a flow blockage accordingly in the rotor passage. Some passive and active flow control methods have already been carried out to manage the tip leakage flow. Winglet-cavity tip, as a passive flow control, has been used to control tip leakage flow and improve aerodynamic performances in turbine cascades. In the present study, large eddy simulation (LES) is used for the flat tip turbine blade, cavity tip turbine blade, and winglet-cavity tip turbine blade. The calculation results of the LES show that, compared with the flat tip blade, the cavity tip blade and the winglet-cavity tip blade change the interaction between the tip leakage and passage vortexes. In the present study, the vortex structure is identified by the Q-criterion. According to the isosurface of Q, the winglet-cavity tip weakens the radial range of interaction between the tip leakage flow and the passage vortex due to its unique tip shape. The winglet structure on the pressure side can effectively reduce the leakage flow rate, and the winglet structure on the suction side changes the position and intensity of the tip leakage flow. After parametric optimization, the winglet-cavity tip shows excellent aerodynamic performances. In the case with a flat tip, the time-averaged total pressure loss coefficient is 10.81%. However, for the cavity and winglet-cavity tips, the time-averaged total pressure loss coefficient decreased by 9.17% and 17.43%, respectively. | |
