Experimental and numerical investigations on the heat transfer of film cooling with cylindrical holes fed with internal coolant cross flows

The heat transfer coefficient of cylindrical holes fed by varying internal cross-flow channels with different cross-flow Reynolds numbers Re_c is experimentally studied on a low-speed flat-plate facility. Three coolant cross flow cases, including a smooth case and two ribbed cases with 45/135-deg ribs, are studied at Re_c ¼ 50,000, and 100,000 with varying blowing ratios M of 0.5, 1.0, and 2.0. A transient liquid-crystal (LC) measurement technique is used to determine the heat transfer coefficient. At lower M, the heat transfer enhancement regions are asymmetrical for the smooth and 45-deg cases. The asymmetrical vortex is more pronounced with increasing cross-flow direction velocity, resulting in a more skewed distribution at Re_c ¼ 100,000. Conversely, the contours are laterally symmetric in the 135-deg case at varying Re_c. A fork-shaped trend with a relatively high heat transfer coefficient appears upstream, and the increases in the heat transfer in the 135-deg cases are lower than those in the 45-deg cases. As M increases to 2.0, the vortex intensity increases, resulting in a stronger scouring effect upstream, especially at large Re_c. The range and degree are affected by Re_c at M ¼ 2.0. The core of the heat transfer enhancement is skewed to the -Y side for both cases.