Presented in this paper is an experimental study focusing on the effects of diffusion hole-geometry on overall film cooling performance. The study consists of three different but closely related hole shapes: (1) Shape A: straight circular hole with a 30 deg inclined injection, (2) Shape B: same as Shape A but with a 10 deg forward diffusion, and (3) Shape C: same as Shape B with an additional 10 deg lateral diffusion. The blowing ratios tested are 0.5 and 1.0. The density ratio is nominally equal to one. Measurements of the experiment use a transient liquid crystal technique that reveals local distributions of both film effectiveness (η) and heat transfer coefficient (h). The data obtained indicate that Shape C with a combined forward and lateral diffusion produces a significant increase in η and decrease in h as compared to Shape A, the baseline case. These improvements combined yield an about 20 percent to 30 percent reduction in heat transfer or thermal load on the film protected surface. Shape B, with forward diffusion only, shows a much less significant change in both film effectiveness and overall heat transfer reduction than Shape C. However, it has the lowest heat transfer coefficient in the vicinity of the injection hole among all the three hole-shapes studied. A flow visualization study using pulsed laser sheet-light reveals that Shape A and Shape B inherit quite similar flow structures. The coolant injected out of Shape C flows much closer to the protected wall than that of Shape A and Shape B.

Issue Section:
Gas Turbine Heat Transfer
Keywords:
Convection, Cooling, Film Cooling, Heat Transfer, Turbines, heat transfer, flow visualisation, cooling
Topics:
Diffusion (Physics), Film cooling, Flow (Dynamics), Heat transfer, Heat transfer coefficients, Shapes, Transients (Dynamics), Liquid crystals, Flow visualization, Temperature, Coolants, Cooling
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