Tip leakage aerodynamics over the cavity squealer tip equipped with full coverage winglets in a turbine cascade

The effect of winglet width-to-pitch ratio, w/p, on tip leakage aerodynamics over the cavity squealer tip equipped with full coverage (FC) winglets for a squealer rim height-to-span ratio of hst/s = 3.75% has been investigated in a turbine cascade for a tip gap-to-span ratio of h/s = 1.36%. Based on near-tip flow visualizations and flow measurements, various tip leakage flow changes by installing the FC winglet on the cavity squealer tip are discussed in detail. With the increment of w/p, the total pressure loss coefficient mass-averaged all over the measurement plane, C‾Pt, for the cavity squealer tip with the FC winglet increases for w/p ⩽ 2.64%, decreases for 2.64% < w/p < 10.55%, and then becomes nearly constant. The maximum reduction of C‾Pt by installing the FC winglet on the cavity squealer tip is 5.8% of C‾Pt for the cavity squealer tip without winglet. This is only almost half of the maximum loss reduction by installing the FC winglet on the plane tip with respect to C‾Pt for the plane tip without winglet. As w/p increases, the FC winglet works better in flow turning within the turbine blade passage.