Near Tip Loss Control With a Winglet Baffle Cavity Tip in a Turbine Cascade

The aerodynamic performance of a winglet baffle cavity tip is investigated at different inlet incidences from -12.5 to +12.5 deg. This blade tip shows a geometry feature with a pressure side winglet and a baffle within the tip cavity. The experimental studies were carried out in a large-scale linear cascade. Numerical methods were also used to obtain the detail flow physics. The baffle on the tip divides the cavity vortex into two main parts, and enhances flow mixing over the tip. As the tip leakage flow exits the tip near the baffle and the cavity corner, flow separation occurs over the suction side and its blockage effect reduces the local tip leakage mass flow rate. The additional pressure side winglet reduces the contraction coefficient on the pressure side squealer. Compared with the squealer tip, the winglet baffle cavity tip reduces the tip leakage mass flow by 12.1% and the near tip loss by 4.2%. Removing the baffle on the tip also results in an increase of the loss. As the incidence of the incoming flow decreases, the loss near the tip reduces mainly due to a reduction of the strength of the passage vortex, which develops from the casing endwall. At all incidences studied, the winglet baffle cavity tip shows better aerodynamic performance than the squealer tip.