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Research Papers: Conduction

Transient Method for Convective Heat Transfer Measurement With Lateral Conduction—Part I: Application to a Deposit-Roughened Gas Turbine Surface

[+] Author and Article Information
J. Bons

 Ohio State University, 2300 West Case Road, Columbus, OH 43235

J. Heat Transfer 131(1), 011301 (Oct 15, 2008) (7 pages) doi:10.1115/1.2976784 History: Received October 10, 2007; Revised May 19, 2008; Published October 15, 2008

The effect of lateral conduction on convective heat transfer measurements using a transient infrared technique over a rough surface is evaluated. The rough surface is a scaled model of gas turbine surface deposits. Comparisons are made between a full 3D finite volume analysis and a simpler 1D transient conduction model. The surface temperature history was measured with a high resolution infrared camera during an impulsively started hot gas flow over the rough test plate at a flow Reynolds number of 750,000. The boundary layer was turbulent with the peak roughness elements protruding just above the boundary layer momentum thickness. The 1D model underestimates the peak to valley variations in surface heat flux by up to a factor of 5 compared with the 3D model with lateral conduction. For the area-averaged surface heat flux, the 1D model predicts higher values than a 3D model for the same surface temperature history. This is due to the larger surface area of the roughness peaks and valleys in the 3D model, which produces a larger initial input of energy at the beginning of the transient. For engineering purposes, where the net heat load into the solid is desired, this lower 3D model result must be multiplied by the wetted-to-planform surface area ratio of the roughness panel. For the roughness model in this study, applying this correction results in a 25% increase in the area-averaged roughness-induced Stanton number augmentation for the 3D rough surface model compared with a flat 1D surface model at the same Reynolds number. Other shortcomings of the transient method for rough surface convective heat transfer measurement are identified.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Rough surface topology showing slice of finite volume grid taken at z=38 mm

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Figure 2

Surface temperature maps for rough surface measured with IR camera: (a) Ts(y,z) at t=50 s and (b) Ts(y,t) at z=38 mm; temperatures in kelvins

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Figure 3

Time-averaged (80<t<100 s) surface heat flux maps, qs(y,z), from (a) 1D method and (b) 3D method for rough surface

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Figure 4

Time-averaged (80<t<100 s) surface heat flux, qs(y), from 1D method and 3D method for rough surface (z=38 mm)

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Figure 5

Area-averaged surface heat flux history from 1D method, 3D method for rough surface, and “area-adjusted” 3D method for rough surface

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Figure 6

Schematic showing section of 3D finite volume grid for smooth versus rough surface

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