Experimental and computational assessment into the heat transfer for the blade multicavity tips

In the gas turbine, the tip region of the shroudless blade is under severe heat load, and thus is seriously ablated. Therefore, an in-depth understanding of the tip heat transfer distributions is of great significance for tip cooling design. In the present work, the heat transfer coefficient distributions of the multicavity tips were measured by a steady-state thermal-analysis method with Infrared camera. The measurements were conducted under two inlet Reynolds number conditions (1.10 x 105, 2.23 x 105) and two tip gaps (1.6 %, 3.5 % Chord length). In addition, the computational simulations verified by the experimental data were conducted to attain the detailed flow field near the tip, and to gain insight into the heat transfer characteristics. Measured results show that additional hot spots are detected behind the rib for the multicavity tips with three or four cavities owing to the leakage flow reattachment. The heat transfer at the suction-side corner is also enhanced by the multicavity tips, whereas a low heat transfer coefficient region is found in the corner in front of the rib. Increasing the inlet Reynolds number would not change the heat transfer patterns, but would evidently increase the heat transfer coefficient values. Adopting a larger tip gap also increases the heat transfer coefficient values, but the effect is not so obviously as the inlet Reynolds number. Compared with the conventional one-cavity tip, the multicavity tips can reduce the aerodynamic losses, and the loss values are reduced by about 2 %.