Numerical investigation on the effects of the divided steps on film cooling performance

Described in this paper is a numerical investigation on the concept for enhancing the film cooling performance by placing divided steps upstream the film cooling hole. Five different divided steps are investigated, including the cases of steps with 2.5 mm, 5 mm, 10 mm, 15 mm divided spacing in the middle, and 2.5 mm divided spacing in both lateral sides. The effects of different divided spacing on film cooling performance are conducted. The film cooling performance on a flat plate and the film cooling with an undivided step are also presented as a contrast. The film cooling performance is evaluated at the density of 0.97 with the blowing ratios ranging from 1.0 to 2.0. Results obtained show that the film cooling performance with the steps divided in the middle is greatly improved when compared with the undivided step. Both the entrainment of coolant and the anti-kidney vortexes are observed in the case of film cooling with divided steps and the film cooling performance is improved by the combined effect of the entrainment and the anti-kidney vortexes. The total pressure loss for film cooling with divided steps is lower than that with undivided step. The film coverage effect and the adiabatic film cooling effectiveness for case with 5 mm divided in the middle of the step are all the best among all the cases.