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-degree inclined injection, (2) Shape B: same as Shape A but with a 10-degree forward diffusion, and (3) Shape C: same as Shape B with an additional 10-degree 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 30% to 50% 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.
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.
This study investigates the effects of pin shape of staggered arrays on heat transfer enhancement. Three different pins: circular, cubic, and diamond, are studied. The arrays consists of twelve rows of five columns with geometry configuration of ST/D = 2.5 and SL/D = 2.5, H/D = 1. Tests were conducted at Reynolds number between 12,000 and 19,000. The heat transfer measurement uses a liquid crystal imaging technique combined with a one-dimensional, transient conduction model and a lumped heat-capacitance model. The results reveal that the heat transfer from the cubic pin arrays and diamond pin arrays is higher than that from the circular pin arrays at the same Reynolds number. However, the circular pin arrays provide the lowest pressure loss among the three arrays. Considering the trade-offs between heat transfer and pumping power, the circular pin arrays may still be the better choice as a heat exchanger.
Described in this paper is an experimental investigation on the effects of flow pulsation on both the film effectiveness and heat transfer coefficient in the vicinity of a row of five injection holes with a 30° inclination relative to the mainstream direction. The experiment uses a transient liquid crystal technique designed for studies of three-temperature convection systems. Generation of pulsation in the mainstream uses a rotating shutter attached at the downstream end of the test channel, which produces a sinusoidal disturbance in both static pressure and mean velocity. The experiment conducted covers a range of Strouhal numbers from 0 to 0.6 and blowing ratios from 0.3 to 1.0, while the Reynolds number is maintained constant at approximately 2,770. The results show that the presence of flow pulsation significantly reduces the magnitudes of film effectiveness. On the other hand, the values of convective heat transfer coefficient appear to increase with the Strouhal number. However, the local heat transfer coefficient immediately downstream to the injection hole is somewhat insensitive to the level of pulsating disturbance.
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