Effects of dislocations on film cooling effectiveness of a laidback fan-shaped hole

The present study numerically investigated the effect of dislocations on the film cooling characteristics under various blowing ratios. The dislocation was between the cylindrical segment and the diffuser segment of the laidback fan-shaped hole. The studied dislocations included that single dislocations in relative X, Y and -Y direction, and combined dislocations in relative Z and X, Z and Y, Z and -Y direction. And three dislocation distances were also studied (5%D, 15%D, 25%D in relative X and Y direction, and 0, 5%D, 10%D in relative Z direction). Results showed that the film cooling effectiveness increased slightly when the dislocation distance was less than 5%D in relative X direction. Otherwise, if the dislocation distance was greater than 5%D, coolant would raise up and mainstream would flow back into the hole channel from the bottom end of the hole. As a result, the film cooling effectiveness decreased sharply and the risk of ablative hole structure also generated. Moreover, the influence of dislocation in relative Y or -Y direction on the film cooling effectiveness was within the range of +/- 10%. 5Y0 showed the best film cooling effectiveness, which was higher than that of the reference case by 1.7%. And the hole with dislocations in relative Y direction could work safely. Whereas, if the dislocation distance was greater than 5%D in relative -Y direction, mainstream would flow black at the upper end of the hole. In addition, the combined dislocations in relative Z direction mainly increased the hole outlet area and could increase the influence on film cooling effectiveness compared to single dislocations. Finally, the film cooling effectiveness of reference case, 5X0, 25Y0 and 5-Y0 all increased with the blowing ratio firstly and then decreased. 5X0 performed the worst film cooling effectiveness, which was decreased by 32.8% compared to reference case when the blowing ratio was 1.5. And the film cooling effectiveness of 5-Y0 almost performed higher than that of the reference case within the range of blowing ratios studied in current paper, which was improved by 9.2% when the blowing ratio was 1.5.