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Research Papers

Large Eddy Simulation of Flow and Heat Transfer in the Developing Flow Region of a Rotating Gas Turbine Blade Internal Cooling Duct With Coriolis and Buoyancy Forces

[+] Author and Article Information
Evan A. Sewall, Danesh K. Tafti

Mechanical Engineering Department, Virginia Tech, Blacksburg, VA 24061

J. Turbomach 130(1), 011005 (Dec 19, 2007) (7 pages) doi:10.1115/1.2437779 History: Received March 17, 2006; Revised June 08, 2006; Published December 19, 2007

The problem of accurately predicting the flow and heat transfer in the ribbed internal cooling duct of a rotating gas turbine blade is addressed with the use of large eddy simulations (LES). Four calculations of the developing flow region of a rotating duct with ribs on opposite walls are used to study changes in the buoyancy parameter at a constant rotation rate. The Reynolds number is 20,000, the rotation number is 0.3, and the buoyancy parameter is varied between 0.00, 0.25, 0.45, and 0.65. Previous experimental studies have noted that leading wall heat transfer augmentation decreases as the buoyancy parameter increases with low buoyancy, but heat transfer then increases with high buoyancy. However, no consistent physical explanation has been given in the literature. The LES results from this study show that the initial decrease in augmentation with buoyancy is a result of larger separated regions at the leading wall. However, as the separated region spans the full pitch between ribs with an increase in buoyancy parameter, it leads to increased turbulence and increased entrainment of mainstream fluid, which is redirected toward the leading wall by the presence of a rib. The impinging mainstream fluid results in heat transfer augmentation in the region immediately upstream of a rib. The results obtained from this study are in very good agreement with previous experimental results.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Developing flow domain consisting of nine ribs followed by a downstream extension region

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Figure 2

Mean velocity profiles along a vertical line between ribs 8 and 9 in the symmetry plane (Ro=0.30 in the rotating cases)

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Figure 3

Streamlines in the symmetry plane of the ducts for buoyancy parameters of 0.00, 0.25, 0.45, and 0.65

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Figure 4

Close-up views of the leading wall recirculating zones

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Figure 5

Vertical profile of turbulent kinetic energy in the symmetry plane (z=0.5) directly between ribs 7 and 8

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Figure 6

Streamlines injected upstream of rib 8 in the four buoyancy cases of (a) Bo=0.00, (b) Bo=0.25, (c) Bo=0.45, and (d) Bo=0.65 (Ro=0.30 in all cases)

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Figure 7

Heat transfer augmentation contours on the leading wall

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Figure 8

Rib-averaged heat transfer augmentation on the leading and trailing walls and a close-up of the leading wall

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Figure 9

Fully developed heat transfer augmentation as compared to previous LES calculations (17,14) and the experiments of Wagner (1)

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Figure 10

The friction factor augmentation for the stationary ribbed case and the four buoyancy cases

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