Optimization of the Coanda bump to improve the film cooling effectiveness of an inclined slot

The present study attempted to improve film cooling effectiveness by installing a Coanda effect-inducing protrusion, called a Coanda bump, at the exit of the 45-degree inclined slot. The inclined slot used in this study was rectangular in shape with dimensions of 4 mm by 50 mm. For optimization, three geometric Coanda bump parameters - the width, height, and streamwise position of the peak point - were selected. The Box-Behnken design (BBD) method was employed to calculate the cases, and the response surface method (RSM) was applied to optimize the Coanda bump. The objective function (i.e., the area averaged film cooling effectiveness) was numerically investigated via a Reynolds-averaged Navier-Stokes (RANS) analysis. The results showed that when the optimized Coanda bump was applied to the slot exit, secondary flows such as the kidney vortex decreased and the coolant lift-off diminished compared to the reference design point without the Coanda bump. The area averaged film cooling effectiveness of the optimized design points improved by about 1.3, 2.4, and 7.6% at blowing ratios of 1.0, 1.5, and 2.0, respectively, compared to that of the reference design point.