Numerical study on the effect of different internal angled ribs on the external film cooling performance

For the blades of gas turbine, the traditional internal ribs have a great impact on the film cooling heat transfer of blade external surface. In this study, SST k-ω turbulence coupled with transition model is adopted to study the effects of angled ribbed passages on external flow and heat transfer characteristics. The detailed flow characteristics were analyzed for two vertically placed flat-plate channels with the blowing ratios of 0.5∼2. The computational model includes a single film hole (D = 20 mm) with a jet angle of 35°. Four different rib orientations in the secondary flow channels are designed. They are no rib, oblique rib 1 (30° angle from the horizontal line), oblique rib 2 (symmetrical to oblique rib 1), and straight rib. Compared with ribless channel, the average adiabatic film cooling effectiveness of straight rib, Oblique rib 1, Oblique rib 2 are 2.3, 2.2, and 1.9 times higher at different Reynolds numbers, respectively. Taking the film hole as the origin, Oblique rib 2 can greatly improve the overall cooling effectiveness. Oblique rib 1 can improve the cooling effectiveness of the farther downstream wall surface. The comparison of film cooling efficiency, coolant coverage area, flow behavior inside the film hole and that in the downstream, heat transfer and transition behavior for different channels are also analyzed separately. Through the investigations, it helps to understand the effects of internal rib angle on the flow, friction factor and heat transfer outside the film holes.