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Research Papers

Film Cooling Effectiveness and Heat Transfer Near Deposit-Laden Film Holes

[+] Author and Article Information
Scott Lewis, Brett Barker, Jeffrey P. Bons

Department of Aerospace Engineering, Ohio State University, Columbus, OH 43235

Weiguo Ai, Thomas H. Fletcher

Department of Chemical Engineering, Brigham Young University, Provo, UT 84602

J. Turbomach 133(3), 031003 (Nov 11, 2010) (9 pages) doi:10.1115/1.4001190 History: Received July 27, 2009; Revised August 21, 2009; Published November 11, 2010; Online November 11, 2010

Experiments were conducted to determine the impact of synfuel deposits on film cooling effectiveness and heat transfer. Scaled up models were made of synfuel deposits formed on film-cooled turbine blade coupons exposed to accelerated deposition. Three distinct deposition patterns were modeled: a large deposition pattern (maximum deposit peak2 hole diameters) located exclusively upstream of the holes, a large deposition pattern (maximum deposit peak1.25 hole diameters) extending downstream between the cooling holes, and a small deposition pattern (maximum deposit peak0.75 hole diameter) also extending downstream between the cooling holes. The models featured cylindrical holes inclined at 30 deg to the surface and aligned with the primary flow direction. The spacing of the holes were 3, 3.35, and 4.5 hole diameters, respectively. Flat models with the same film cooling hole geometry and spacing were used for comparison. The models were tested using blowing ratios of 0.5–2 with a turbulent approach boundary layer and 0.5% freestream turbulence. The density ratio was approximately 1.1 and the primary flow Reynolds number at the film cooling row location was 300,000. An infrared camera was used to obtain the film cooling effectiveness from steady state tests and surface convective heat transfer coefficients using transient tests. The model with upstream deposition caused the primary flow to lift off the surface over the roughness peaks and allowed the coolant to stay attached to the model. Increasing the blowing ratio from 0.5 to 2 only expanded the region that the coolant could reach and improved the cooling effectiveness. Though the heat transfer coefficient also increased at high blowing ratios, the net heat flux ratio was still less than unity, indicating film cooling benefit. For the two models with deposition between the cooling holes, the freestream air was forced into the valleys in line with the coolant holes and degraded area-averaged coolant performance at lower blowing ratios. It is concluded that the film cooling effectiveness is highest when deposition is limited to upstream of the cooling holes. When accounting for the insulating effect of the deposits between the film holes, even the panels with deposits downstream of the film holes can yield a net decrease in heat flux for some cases.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 8

Area-averaged convective heat transfer ratio versus M (0.5<x/d<7). Both smooth and deposit panels.

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Figure 9

Area-averaged rough-to-smooth convective heat transfer ratio versus M (0.5<x/d<7). Comparison at constant blowing ratio.

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Figure 10

Area-averaged heat flux ratio versus M (0.5<x/d<7). Both smooth and deposit panels.

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Figure 11

Area-averaged rough-to-smooth heat flux ratio versus M (0.5<x/d<7). Comparison at constant blowing ratio.

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Figure 12

Contour plot of hR/hRo for s/d=4.5, M=1 (0.5<x/d<7, −4.5<y/d<4.5). Flow is left to right.

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Figure 3

Film cooling wind tunnel test section diagram

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Figure 2

Digital images of the stereolithography models corresponding to the deposit patterns in Fig. 1: (a) s/d=3.0, (b) s/d=3.35, and (c) s/d=4.5

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Figure 1

After deposition photographs of the three turbine blade coupons: (a) s/d=4.5, (b) s/d=3.35, and (c) s/d=4.5

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Figure 7

Area-averaged film effectiveness versus M (0.5<x/d<7). Both smooth and deposit panels.

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Figure 6

Film effectiveness contour maps for smooth and deposit panels at M=1 (flow is left to right): (a) s/d=3.0, (b) s/d=3.35, and (c) s/d=4.5

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Figure 5

Area-averaged film effectiveness, heat transfer coefficient ratio, and heat flux ratio versus M (0.5<x/d<7). Smooth panels only.

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Figure 4

Spanwise-averaged film effectiveness at x/d=5 for present study versus Brown and Saluja (23). Smooth panels only.

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