Blade Tip Leakage Flow and Heat Transfer With Pressure-Side Winglet

Abstract

A numerical study has been conducted to explore the effect of a pressure-side winglet on the flow and heat transfer over a blade tip. Calculations are performed for both a flat tip and a squealer tip. The winglet is in the form of a flat extension, and is shaped in the axial chord direction to have the maximum thickness at the chord location where the pressure difference is the largest between the pressure and suction sides. For the flat tip, the pressure side winglet exhibits a significant reduction in the leakage flow strength and an associated reduction in the aerodynamic loss. The low heat transfer coefficient “sweet-spot” region is larger with the pressure-side winglet, and lower heat transfer coefficients are also observed along the pressure side of the blade. The winglet reduces the average heat transfer coefficient by about 7%. In the presence of a squealer, the role of the winglet decreases significantly, and only a 0.5% reduction in the pressure ratio is achieved with the winglet with virtually no reduction in the average heat transfer coefficient.

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

“…Papa et al (2003) measured heat/mass transfer data on the tip surface having both a suction-side squealer and a pressure-side winglet. Saha et al (2006) explored the effect of a pressure-side winglet on the flow and heat transfer over a plane, cavity squealer, and suction-side squealer tips. Harvey et al (2006aHarvey et al ( , 2006b) tested a winglet with gutter numerically and experimentally in a high-speed rotating environment, and they found that the winglet is as good as a shroud with two fins in the reduction of over-tip leakage loss.…”

Experimental investigation of effects of suction-side squealer tip geometry on the flow field in a large-scale axial compressor using SPIV

“…The results show that the latter tip configuration exerted positive effects on the local aerodynamic field by means of weakening the tip leakage vortex. Such tip treatments could also be a promising measure to improve the heat transfer of the turbine blade tip [8][9][10]. The existing literature towards the application of this passive flow control technology in compressors is relatively less.…”

Numerical investigation of active tip-clearance control through tip cooling injection in an axial turbine cascade

“…The most familiar method is to modify blade tip geometry, including winglet [4] , squealer tips [5] , blade tip chamfering [6] . Results indicated that all these modifications could reduce the strength of tip clearance flow and local heat transfer coefficient on the blade tip surface.…”