A NUMERICAL STUDY ON INCREASING FILM COOLING EFFECTIVENESS THROUGH THE USE OF SISTER HOLES

Film cooling has been the primary focus of turbine blade cooling research for the past half century. However, as engines become more powerful, more effective non-traditional means of cooling become necessary. The current study branches out into a new scheme for film cooling; sister holes. The geometry of the current work makes use of three cylindrical holes inclined at 35 to the horizontal: one primary injectant hole bound by two sister holes. Numerical simulations were run with blowing ratios varying from M = 0.2 to M = 1.5, using the realizable k-epsilon turbulence model with near-wall modeling. The results were analyzed for both adiabatic thermal effectiveness as well as vortex production due to flow mixing. In general, sister holes offer significant advantages in thermal protection over their single hole counterparts both laterally and along the centre-line, particularly in regions close to the hole. Simulations showed that the laterally averaged adiabatic thermal effectiveness increased by a factor of 1.35 for M = 0.2 up to a factor of 1.62 for M = 1.5. Similarly, the centre-line effectiveness increased by a factor of 1.22 at M = 0.2 up to a factor of 1.68 at M = 1.5. These benefits are heavily weighted by the near-hole region; however, increases are evident throughout the computational domain. This sister hole technique offers significant advantages with minimal penalties, making it a valuable candidate for future blade cooling applications.