Local heat transfer coefficient and film effectiveness distributions on a cylindrical leading edge model using a transient liquid crystal image method
The effect of free-stream turbulence on a film-cooled turbine blade leading edge model is studied using a transient liquid crystal technique. High free-stream turbulence was produced using two different grid sizes with the leading edge simulated by a cylinder in a cross flow. Mainstream Reynolds number based on the cylinder diameter was 100,000. Detailed distributions of the film effectiveness and heat transfer coefficient were obtained for five blowing ratios of 0.2, 0.4, 0.6, 0.8, and 1.2. Two rows of holes at 15 from stagnation with holes in each row spaced four-hole diameters apart and were angled at 30 and 90 to the surface in the spanwise and streamwise directions, respectively. The cylinder, coated with a thin layer of liquid crystals, is heated to a uniform temperature and suddenly exposed to a cooler mainstream, the time history of color change at each pixel is analyzed to obtain the local heat transfer coefficient and film effectiveness. Results show that the heat transfer coefficient increases with an increased blowing ratio but the film effectiveness reaches a peak value at a blowing ratio of 0.4. Results also show that higher free-stream turbulence reduces film effectiveness for lower blowing ratios but the effect diminishes at higher blowing ratios.