High resolution measurements of film cooling performance of simple and compound angle cylindrical holes with varying hole length-to-diameter ratio-Part I: Adiabatic film effectiveness

Adiabatic film cooling effectiveness on a flat plate surface downstream a row of simple and compound angle holes was investigated using high-resolution pressure sensitive paint (PSP) technique. A variation of flow parameters including density ratio and blowing ratio, and geometry parameters including compound angle and length-to-diameter ratio were examined. Blowing ratios (M) ranging from 0.3 to 2, density ratio (DR) are 1.0 and 1.5, length to diameter ratios (L/D) from 0.5 to 5 and two compound angle (beta: 0 degrees, 45 degrees) were employed composing a test matrix of 140 test cases. Discharge coefficient was measured with varied blowing ratio and L/D values for simple and compound angle hole, Detailed local, laterally averaged, and area averaged film effectiveness are presented to illustrate the effect of length-to-diameter ratio and compound angle. It was found that the effect of density ratio on the film cooling effectiveness was associated with the blowing ratio. Increasing density ratio provides a negative effect when the M <= 0.5 for simple and compound angle hole, Which a positive effect when the M > 0.5. Also found was that the film effectiveness was highest when L/D = 0.5 and 1, regardless of blowing ratio and compound angle. The film cooling effectiveness of simple angle hole increased as L/D increased from 2 to 5 when M <= 1, while showed a minimum value at L/D = 3.5 when M >= 1. The film cooling effectiveness of compound angle hole showed a minimum value at L/D = 3,5 regardless of blowing ratio. The scaling methods of film effectiveness with velocity ratio, blowing ratio, and momentum flux ratio were also discussed for simple angle and compound angle holes with varying L/D.