Effect of ejection angle and blowing ratio on heat transfer and film cooling effect on a winglet tip

Effects of ejection angle and blowing ratio on heat transfer and film cooling effect on a winglet tip were numerically investigated with the RANS (Reynolds Averaged Navier-Stokes) equations solutions. The total pressure loss in cascade, and heat transfer coefficient and film cooling effectiveness on the winglet tip with both tip and pressure side holes were computed at a range of pitchwise ejection angles and streamwise ejection angles. At three blowing ratios (M = 0.5, 1.0, 2.0), the sensitivity of heat transfer coefficient and film cooling effectiveness distributions on winglet tip to the variation of blowing ratio was also investigated. The results indicate that the heat transfer coefficient and film cooling effectiveness on the winglet tip are much sensitive to the pitchwise and streamwise ejection angles and blowing ratio. A better heat transfer and film cooling effect on the winglet tip can be achieved as the pitchwise ejection angle is less than 30° and streamwise ejection angle is around 120°. The heat transfer and film cooling effect on winglet tip is not sensitive to the pitchwise ejection angle if it is larger than 45°. If vertical ejection direction is chosen for the cooling flow, a small blowing ratio (M = 0.5 in this study) is beneficial for the reduction of disturbance to pass-over leakage. However, in the case of a small pitchwise ejection angle, a medium blowing ratio (M = 1.0 in this study) is profitable to gain a wider coolant coverage on the cavity floor in pitchwise direction.