Film-Cooling Performance of Antivortex Hole on a Flat Plate

Improved film cooling performance and coolant flow usage have a significant effect on overall engine performance. In the current study, film cooling performance of an improved antivortex or tripod hole geometry is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique and compared to traditional baseline geometry. The baseline geometry is a simple cylindrical hole design inclined at 30 deg from the surface with pitch-to-diameter ratio of 3.0. The proposed improvement is a tripod design where the two side holes, also of the same diameter, branch out from the root of the main hole at 15 deg angle with a larger pitch-to-diameter ratio of 6.0 between the main holes. The third geometry studied is the same tripod design embedded in a trench to enhance two-dimensional film performance. The mainstream Reynolds number is 3110 based on the coolant hole inlet diameter. 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 indicate significant improvement in effectiveness with the tripod holes compared to cylindrical holes at all the blowing ratios studied. The trenched design shows improved effectiveness in the trench region and reduced effectiveness in the downstream region. At any given blowing ratio, the tripod hole designs use 50% less coolant and provide at least 30%-40% overall averaged higher cooling effectiveness. The use of relatively dense secondary fluid improves effectiveness immediately downstream of the antivortex holes but leads to poor performance downstream.