Study on the film cooling effectiveness of shaped holes in the suction surface gill region of the turbine blade

In the suction surface gill region of the turbine blade, three representative regions with a favorable pressure gradient (FPG), adverse pressure gradient (APG), and pressure gradient transition (from FPG to APG) were chosen to explore the film cooling characteristics. A row of 11-11-11 holes (a modified hole of 7-7-7 holes with a spanwise expansion angle and a streamwise expansion angle of 11 degrees) was set up in these three regions. The distribution of film cooling effectiveness (eta) in three different regions was explored using the pressure sensitive paint (PSP) technique. On this basis, a row of cylindrical holes was set in both regions with pressure gradient transition and APG on the suction surface of the turbine blade. The difference in film cooling characteristics between the 11-11-11 hole and the cylindrical hole was analyzed. Meanwhile, numerical calculations of the experimental model were carried out to analyze the flow and mixing characteristics of the cooling jet in the three regions. The laterally averaged eta of the 11-11-11 hole in the region with FPG is higher than that in the region with pressure gradient transition and APG under each blowing ratio. It was found that the film coverage was promoted along the flow direction in the region with FPG on the turbine blade. In the region with APG, film coverage was suppressed along the flow direction. However, APG slightly enhances film coverage in the spanwise direction and significantly enhances film coverage in the wall-normal direction. In the region with APG, 11-11-11 holes have an advantage over cylindrical holes only in the near-hole limiting area.