Research Papers

Establishing a Methodology for Resolving Convective Heat Transfer From Complex Geometries

[+] Author and Article Information
Jason K. Ostanek, Karen A. Thole

Department of Mechanical and Nuclear Engineering, Pennsylvania State University, State College, PA 16803

J. Prausa, A. Van Suetendael

 Pratt & Whitney, P.O. Box 109600 M/S 724-25, West Palm Beach, FL 33410-9600

J. Turbomach 132(3), 031014 (Apr 02, 2010) (10 pages) doi:10.1115/1.3144989 History: Received August 19, 2008; Revised February 27, 2009; Published April 02, 2010; Online April 02, 2010

Current turbine airfoils must operate at extreme temperatures, which are continuously driven higher by the demand for high output engines. Internal cooling plays a key role in the longevity of gas turbine airfoils. Ribbed channels are commonly used to increase heat transfer by generating turbulence and to provide a greater convective surface area. Because of the increasing complexity in airfoil design and manufacturing, a methodology is needed to accurately measure the convection coefficient of a rib with a complex shape. Previous studies that have measured the contribution to convective heat transfer from the rib itself have used simple rib geometries. This paper presents a new methodology to measure convective heat transfer coefficients on complex ribbed surfaces. The new method was applied to a relatively simple shape so that comparisons could be made with a commonly accepted method for heat transfer measurements. A numerical analysis was performed to reduce experimental uncertainty and to verify the lumped model approximation used in the new methodology. Experimental measurements were taken in a closed-loop channel using fully rounded discontinuous skewed ribs oriented 45 deg to the flow. The channel aspect ratio was 1.7:1 and the ratio of rib height to hydraulic diameter was 0.075. Heat transfer augmentation levels relative to a smooth channel were measured to be between 4.7 and 3 for Reynolds numbers ranging from 10,000 to 100,000.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Schematic of new methodology

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Figure 2

(a) Nondimensional temperature along the rib centerline at Re=1.0×104 and (b) nondimensional temperature along the rib centerline at Re=1.0×105

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Figure 3

Two successive design iterations showing a reduced contact length for the new methodology

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Figure 4

Percent heat loss versus the Reynolds number for the two-dimensional ANSYS model

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Figure 5

Nondimensional contour plots for various design iterations at Re=1.0×104

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Figure 6

Three-dimensional ribbed model

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Figure 7

Comparison of percent heat loss between the two- and three-dimensional models

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Figure 8

Variation in augmentation factor for various circumferential and spanwise locations for Re=1.0×105

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Figure 9

Percent heat loss versus Reynolds number for different convection coefficient distributions

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Figure 10

Nondimensional temperature along the span of the rib (three-dimensional model, y/e=0.5)

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Nondimensional temperature contours (three-dimensional model, s′/L=0.5)

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Figure 12

Thermocouple locations within 3D ANSYS model for checking location sensitivity

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Figure 13

Thermocouple locations used experimentally to determine the rib-averaged convection coefficient

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Figure 14

Measurement error for different thermocouple locations

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Figure 15

Schematic of validation methodology

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Figure 16

Schematic of experimental facility (18)

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Figure 17

(a) Large scale ribbed model with four Indalloy ribs placed in a foam endwall and (b) large scale ribbed model with four foam ribs encased in Inconel foil

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Figure 18

Nondimensional temperature at center of rib (y/e=0.5) captured at various spanwise locations for Re=1.0×104 and 1.0×105

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Figure 19

Augmentation factor of four ribs using the new and validation methods (Re=2.5×104)

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Figure 20

Augmentation factor for the new and validation methodologies



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