Tip Leakage Flow and Loss in a Turbine Cascade Equipped with Overhang Squealer Tips

Abstract

Tip leakage flow and loss over an overhang squealer tip have been investigated in a turbine blade cascade for a tip gap-to-span ratio of h/s = 1.0%. For an overhang width-to-pitch ratio of 9.9%, squealer rim-height-to-span ratio is changed to be h(st)/s = 0.94%, 1.88%, 3.75%, and 5.63%. The present oil film surface flow visualization provides qualitative flow patterns over the tip surface of the overhang squealer tip. Three-dimensional flow measurements show that the mass-averaged total pressure loss coefficient increases in linear proportion to hst/s. The mass-averaged loss for the overhang squealer tip is lower than that for the plane tip by 7.8% in the case of the lowest squealer rim of h(st)/s = 0.94% but becomes larger than that for the plane tip in the case of h(st)/s = 5.63%. In the reduction of tip leakage loss, the overhang squealer tip with trailing edge opening performs better than the overhang squealer tip with trailing edge closure.