Study of utilizing double lateral sub holes at different spanwise angles on blade film cooling effectiveness

A numerical study of the effect of using double lateral sub-holes at different span-wise angles on flow structure and film-cooling performance is performed. The lateral angles for each sub-hole change from 10° to 20° at the same film-hole diameter (12.7 mm) and jet angle (35°). The flow-field analysis and the performance of film-cooling for the double lateral sub-hole models are investigated comparing with the basic single-hole model. There are high augmentations in the overall effectiveness of film-cooling by 14.2%, 26.5%, and 37.2% for the first, the second, and the third double lateral sub-hole models, respectively when the blowing ratio increases from 0.5 to 1.0. By evaluating the film-cooling performance for the third double lateral sub-hole model compared to the basic model, there is an increasing ratio in the overall effectiveness by 54.2% and 149.5% for the low and high ratio of blowing, respectively. Consequently, the third double lateral sub-hole model can be selected as the best model among the other models and by further operating at a broad range of blowing ratios from 0.25 to 3.5, the model achieves a maximum value of overall film-cooling effectiveness of 44% at an optimum value of blowing ratio 2.5.