Effect of Breakout Angle on Tripod Injection Hole Geometries on Flat Plate Film Cooling

In this study, effect of breakout angle of side holes from the main hole in a tripod hole design on film cooling performance is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique. The designs are compared a cylindrical hole design inclined at 30° from the surface with pitch-to-diameter ratio of 3.0 and a shaped hole design, which is identical to the cylindrical hole design with the addition of adding a 10° flare and laydown to the exit on the mainstream surface. The two tripod hole designs are one where the two side holes, also of the same diameter, branch from the root at a 15° angle while maintaining the same 30° inclination as the cylindrical and shaped designs witha pitch-to-diameter ratio between the main holes for this design is 6.0. The other tripod hole design is a modified tripod hole design that increases the branch angle to 30°, which has the added effect of increasing the pitch-to-diameter ratio between the main holes to 7.5. Two secondary fluids — air and carbon-dioxide — were used to study the effects of coolant-to-mainstream density ratio (DR = 0.95 and 1.45) on film cooling effectiveness. Several blowing ratios in the range 0.5–4.0 were investigated independently at the two density ratios. Results show that the tripod hole design provides similar film cooling effectiveness as the shaped hole case with overall reduced coolant usage. Increasing the breakout angle from 15° to 30° reduces overall cooling effectiveness but increases jet-to-jet interactions.