Numerical investigation of sweeping jet film cooling on a flat plate

A sweeping jet generated by a unique class of fluidic device commonly known as a fluidic oscillator is applied to the film cooling in this study. Unsteady Reynolds-averaged Navier-Stokes numerical simulations are conducted to reveal the film cooling mechanism of the sweeping jet. A comparative study of the sweeping jet and fan-shaped holes film is performed. The innovation and application of sweeping jets can improve the film attachment along flow and span-wise direction. Compared with the fan-shaped hole, the spatially-averaged film cooling effectiveness of the SJ hole increases 34% when the blow ratio is 0.5. Significantly, it is found that the rotating direction of the vortex pair induced by the sweeping jet is contrary to the conventional counter-rotating vortex pair. The anti-counter-rotating vortex pair prevents the wall intrusion of high-temperature flow. The effects of coolant incident angle (alpha = 10 degrees similar to 30 degrees), exit fan angle (beta = 30 degrees similar to 70 degrees) and coolant gas outlet width (L = 0.5D similar to 2D) on the sweeping jet film cooling characteristics are investigated. When the sweeping jet incident angle a is changed from 10 degrees to 30 degrees, the position of higher cooling effectiveness changes from the centerline to both sides of the film hole, and the effectiveness at the centerline is reduced. The sweeping jet spreading angle (beta(jet)) does not follow the exit fan angle beta after beta > 60 degrees, which implies that the jet would not spread any further. Reducing the sweeping jet outlet width can increase the lateral cooling effectiveness. However, the cooling effectiveness of the flow direction shows a decreasing trend when the sweeping jet outlet width is reduced to 0.5D.