Experimental Investigation of Longitudinal Tabs Effects on Film-Cooling Effectiveness of Pea Shaped Holes in Gas Turbine Blades

In this research, the film cooling effectiveness resulting from Pea-shaped holes equipped with the longitudinal tabs at the jet exit region are investigated experimentally applying the infrared thermography method. The measurements are performed at Re = 10000 (based on the free stream characteristics and the jet hole equivalent diameter) and the injection angle of 30˚ over the test plate applying the Pea-shaped jet holes. Several cases are investigated including three different tab heights (0.345 D, 0.522 D, 0.696 D), three different distances between adjacent tabs (0.8D, 1D, 1.2D), and three different tab lengths (8D, 16D, 24D), in which, D is the equivalent diameter of the Pea-shaped hole. Blowing ratio effects are studied in four different cases of 0.4, 0.5, 0.7 and 0.8. The obtained results showed that the applied tabs, by controlling the injected jet flow, highly increase the film cooling effectiveness. At the best blowing ratio of each configuration, the cooling effectiveness averaged over the downstream region of the jet exit increases 44.4 percent for the holes equipped with the tabs, in comparison to the conventional holes. In fact, these tabs prevent the mixing of the hot gases with the cooling jets by controlling the counter rotating vortices and restricting the cooling jet diffusion.