Film cooling effectiveness from trenched shaped and compound holes

This paper presents a comparative-numerical investigation on film cooling from a row of simple and compound-angle holes injected at 35 degrees on a flat plate with four film cooling configurations: (1) cylindrical film hole; (2) 15 degrees forward diffused film hole; (3) trenched cylindrical film hole; (4) trenched 15 degrees forward-diffused film hole. All simulations are at fixed density ratio of 1.6, blowing ratio of 1.25, length-to-diameter LID = 4 and pitch-to-diameter ratio of 3.0. The effect of length-to-diameter ratio on film cooling has been also investigated using LID in the range of 1-8. Computational solutions of the steady, Reynolds-averaged Navier-Stokes equations have been obtained using a finite volume method. It has been found that the shape of the hole and the trenched holes can significantly affect the film cooling flow over the protected surface. Further, it has been shown that the film cooling effectiveness by trenched shaped holes is higher than all other configurations both in spanwise and streamwise specially downstream of the injection. Also, a trenched compound angle injection shaped hole produces much higher film cooling protection than the other configurations investigated in the present paper. The length-to-diameter ratio of trenched holes was found to have a significant effect on film cooling effectiveness and the spread of the coolant jets.