Investigations into heat transfer and film cooling effect on winglet-squealer tips in a turbine stage

Abstract

Heat transfer and film cooling effect on three kinds of winglet-squealer tips (i.e. conventional squealer tip, no P.S. rim tip and P.S. winglet tip) in a turbine stage are numerically investigated at two operation conditions (i.e. laboratory testing condition and sea-level take-off condition) and three cooling-hole arrangements (i.e. un-cooled, with tip holes, and with both tip and pressure side holes), and the numerical results are also compared with those in stationary cascades. To reduce the heat transfer while enhancing film cooling effect on the P.S. winglet tip, ejection angles for the tip and pressure side cooling holes are varied to reveal the superior performance of P.S. winglet tip in turbine stage. The results show that the heat transfer coefficient and film cooling effectiveness distributions on three kinds of tips exhibit different trends in the stationary and rotating cases. Tip rotating significantly affects the trajectories of cooling flow in the conventional squealer tip and no P.S. rim tip due to different vortex system induced in the cavity. However, the relative rotating has little influence on the flow structures in the P.S. winglet tip. In un-cooled condition, the area-averaged heat transfer coefficient on P.S. winglet tip is lower than the conventional squealer tip by 11.6%. For the vertical ejection case in turbine stage, the P.S. winglet tip has a slightly worse heat transfer and film cooling effect than the conventional squealer tip. However, with inclined ejections, the area-averaged heat transfer coefficient on winglet tip in turbine stage is lower than the conventional squealer tip by 15.3%, and the area-averaged film cooling effectiveness on winglet tip is higher than the conventional squealer tip by 12.1%.

Modifications of double-rim geometry to improve thermal performance of squealer tip in a turbine stage

“…Based on the authors’ previous research on turbulence model comparison with respect to the heat transfer coefficient and film cooling effectiveness predictions for the conventional squealer tip, 21 the k-ω turbulence model was adopted in the present numerical simulations. With the k-ω turbulence model, the heat transfer coefficients on the conventional squealer tip are computed at two blowing ratios M = 1 and M = 2 and compared to the experimental data, as shown in Figure 5.…”

“…Apart from the aerodynamic research, the studies for heat transfer and film cooling effect on winglet squealer tip were also under active research in the last two decades. Most of the researchers were aiming at showing the improved thermal performance of winglet tip compared to the flat tip or conventional squealer tip, such as Papa et al, 15 Silva and Tomita, 16 Zhou et al, 17 and Yan et al 18 The other researchers, such as Zhou et al 19 and Yan et al, 20,21 were mainly concentrating on revealing the effects of cooling arrangement, blowing ratio and winglet geometry on the heat transfer and film cooling effectiveness on the winglet tip.…”