FLOWFIELD MEASUREMENTS FOR FILM-COOLING HOLES WITH EXPANDED EXITS

One viable option to improve cooling methods used for gas turbine blad es is to optimize the geometry of the film-cooling hole. To optimize t hat geometry, effects of the hole geometry on the complex jet-in-cross flow interaction need to be understood. This paper presents a comparis on of detailed flowfield measurements for three different single, scal ed-up hole geometries, all at a blowing ratio and density ratio of uni ty. The hole geometries include a round hole, a hole with a laterally expanded exit, and a hole with a forward-laterally expanded exit. In a ddition to the flowfield measurements for expanded cooling hole geomet ries being unique to the literature, the testing facility used for the se measurements was also unique in that both the external mainstream M ach number (Ma(infinity) = 0.25) and internal coolant supply Mach numb er (Ma(c) = 0.3) were nearly matched. Results show that by expanding t he exit of the cooling holes, both the penetration of the cooling jet and the intense shear regions are significantly reduced relative to a round hole. Although the peak turbulence level for all three hole geom etries was nominally the same, the source of that turbulence was diffe rent. The peak turbulence level for both expanded holes was located at the exit of the cooling hole resulting from the expansion angle being too large. The peak turbulence level for the round hole was located d ownstream of the hole exit where the velocity gradients were very larg e.