Design of sister hole arrangements to reduce kidney vortex for film cooling enhancement

In this study, we investigated whether vortex control of forward and backward injection jets with different vortex strengths contributed to enhanced film cooling effectiveness. Various hole arrangements, composed of primary and sister holes, were used to control vortex strengths and vortex interactions between film cooling jets. Numerical simulations were conducted to obtain and analyze the flow characteristics and film cooling effectiveness of six sister hole arrangements, composed of forward and backward injection holes, for blowing ratios of 1 and 2. Hole arrangements with backward injection holes showed improved film cooling effectiveness and laterally wide coverage of film cooling jets. Hole arrangements with forward injection primary holes and backward injection sister holes showed coverage of the entire surface by the film cooling jets, due to the backward injection jets from sister holes and the formation of outward vortexes. Additionally, the other hole arrangement, consisting of forward injection sister holes in the first row and backward injection primary holes in the second row, produced an anti-kidney vortex and improved film cooling effectiveness at high blowing ratios.