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TECHNICAL PAPERS

Experimental Measurements and Modeling of the Effects of Large-Scale Freestream Turbulence on Heat Transfer

[+] Author and Article Information
A. C. Nix1

Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506-6106andrew.nix@mail.wvu.edu

T. E. Diller, W. F. Ng

Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

1

Corresponding author.

J. Turbomach 129(3), 542-550 (Oct 05, 2006) (9 pages) doi:10.1115/1.2515555 History: Received March 03, 2006; Revised October 05, 2006

The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. High-intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after passing through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10–12% and an integral length scale of 2cm(Λxc=0.15) near the entrance of the cascade passages. Mean heat transfer results with high turbulence showed an increase in heat transfer coefficient over the baseline low turbulence case of approximately 8% on the suction surface of the blade, with increases on the pressure surface of approximately 17%. Time-resolved surface heat transfer and passage velocity measurements demonstrate strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations and length scale. The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane, and turbine blade) and boundary layer conditions.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cascade test section and turbulence grid

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Figure 2

Instrumented turbine blade

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Figure 3

Blade surface gauges and passage hot-wire probe

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Figure 4

Comparison of velocity and heat flux time signals. Velocity (top line); heat flux (bottom line).

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Figure 5

Comparison of velocity and heat flux spectra. Velocity (top line); heat flux (bottom line).

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Figure 6

Coherence between velocity and heat flux signals

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Figure 7

Comparison of model predicted and measured Stanton numbers (St) from Radomsky and Thole (2)

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