Numerical investigation of area ratio on sister hole film cooling

A numerical study was performed to investigate the effect of the area ratio at sister hole applications on film cooling effectiveness and flow structure. Two secondary coolant holes are placed on both sides of the main hole at a lateral distance of one main hole diameter. Four different area ratios (AR = 2–5) on the flat plate and two area ratios (AR=2 and 5) on the turbine blade were studied. A single cylindrical hole was also studied for comparison and baseline. Four different blowing ratios (M=0.25,0.5,0.8,1 for the flat plate and M= 0.5,0.75,1,1.5 for the turbine blade) were studied. The results obtained were interpreted through cooling effectiveness and vortex structure. The interaction of vortex and anti-vortex on sister holes was investigated. Temperature contours and streamlines (or velocity vectors) were investigated at different streamwise locations to examine film structure. The area ratio on sister hole applications heavily affects the vortex intensity and size. Therefore, it has a significant effect on the film structure and cooling effectiveness. The positive effect of sister holes is more pronounced at low area ratios. At AR=2, the cooling effectiveness increases by an average of 57% depending on the blowing ratio, while at AR=5 effectiveness increases by 35%. AR has an important place on vortex position, size, and intensity. The results of this study showed area ratio, as well as the lateral distance between main hole and sister hole centers heavily affects the cooling effectiveness, the lower area ratios are more efficient for film cooling.