Research Papers

An Investigation of Treating Adiabatic Wall Temperature as the Driving Temperature in Film Cooling Studies

[+] Author and Article Information
Lei Zhao

 Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148-2220

Ting Wang1

 Energy Conversion and Conservation Center, University of New Orleans, New Orleans, LA 70148-2220twang@uno.edu


Corresponding author.

J. Turbomach 134(6), 061032 (Sep 17, 2012) (9 pages) doi:10.1115/1.4006311 History: Received July 19, 2011; Revised July 29, 2011; Published September 17, 2012

In film cooling heat transfer analysis, one of the core concepts is to deem film cooled adiabatic wall temperature (Taw ) as the driving potential for the actual heat flux over the film-cooled surface. Theoretically, the concept of treating Taw as the driving temperature potential is drawn from compressible flow theory when viscous dissipation becomes the heat source near the wall and creates higher wall temperature than in the flowing gas. But in conditions where viscous dissipation is negligible, which is common in experiments under laboratory conditions, the heat source is not from near the wall but from the main hot gas stream; therefore, the concept of treating the adiabatic wall temperature as the driving potential is subjected to examination. To help investigate the role that Taw plays, a series of computational simulations are conducted under typical film cooling conditions over a conjugate wall with internal flow cooling. The result and analysis support the validity of this concept to be used in the film cooling by showing that Taw is indeed the driving temperature potential on the hypothetical zero wall thickness condition, i.e., Taw is always higher than Tw with underneath (or internal) cooling and the adiabatic film heat transfer coefficient (haf ) is always positive. However, in the conjugate wall cases, Taw is not always higher than wall temperature (Tw ), and therefore, Taw does not always play the role as the driving potential. Reversed heat transfer through the airfoil wall from downstream to upstream is possible, and this reversed heat flow will make Tw  > Taw in the near injection hole region. Yet evidence supports that Taw can be used to correctly predict the heat flux direction and always result in a positive adiabatic heat transfer coefficient (haf ). The results further suggest that two different test walls are recommended for conducting film cooling experiments: a low thermal conductivity material should be used for obtaining accurate Taw and a relative high thermal conductivity material be used for conjugate cooling experiment. Insulating a high-conductivity wall will result in Taw distribution that will not provide correct heat flux or haf values near the injection hole.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Qualitatively temperature profiles of a typical internally and film cooled blade at two locations: one near the injection hole region with potentially reversed heat transfer and the other located further downstream. The axial heat conduction transfer is small and the size of reversed heat flux arrowhead is enlarged for illustration purpose.

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Figure 2

Computational domains for 2D and 3D, respectively

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Figure 3

(a) Computational Meshes for 2D and 3D, respectively (b) Comparison of CFD result with the experiment result of Goldstein [15]

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Figure 4

Illustration of approach two

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Figure 5

Illustrations of boundary condition and wall thickness treatment for different cases

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Figure 6

(a) Adiabatic wall temperatures, conjugate wall temperature and heat flux in two y-axes (b) Zoom-in view of (a) in near injection hole region (c) Film cooling effectiveness (ϕ) and adiabatic film cooling effectiveness (η)

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Figure 7

Heat flux, wall temperatures from Cases 4.1, 4.2 and 4.3 with Taw from the baseline case (Case1)

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Figure 8

Comparison between the actual driving temperature and Taw in the 2D Study

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Figure 9

Heat flux, wall temperatures from 3D Cases (a) Cases 6.1, 6.2 and 6.3 (b) Cases 7a and 7b. Taw along the centerline through the center of the hole from the 3D baseline case (Case5) and 2D baseline case (Case1) are also included for comparison. Heat flux plotted on secondary axis on the right.

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Figure 10

Test surface temperature contours of Case 3 (2D) and Case 5 (3D)

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Figure 11

Comparison between the actual driving temperature and Taw in 3D Study




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