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Research Papers

Experimental Study of Surface Roughness Effects on a Turbine Airfoil in a Linear Cascade— Part I: External Heat Transfer

[+] Author and Article Information
M. Lorenz

Institut für Thermische Strömungsmaschinen, Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germanymarco.lorenz@kit.edu

A. Schulz

Institut für Thermische Strömungsmaschinen, Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germanyachmed.schulz@kit.edu

H.-J. Bauer

Institut für Thermische Strömungsmaschinen, Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germanyhans-joerg.bauer@kit.edu

J. Turbomach 134(4), 041006 (Jul 20, 2011) (11 pages) doi:10.1115/1.4003234 History: Received September 07, 2010; Revised October 25, 2010; Published July 20, 2011; Online July 20, 2011

The present experimental study is part of a comprehensive heat transfer analysis on a highly loaded low pressure turbine blade and endwall with varying surface roughness. Whereas a former paper (Lorenz, 2009, “An Experimental Study of Airfoil and Endwall Heat Transfer in a Linear Turbine Blade Cascade—Secondary Flow and Surface Roughness Effects,” International Symposium on Heat Transfer in Gas Turbine Systems, Aug. 9–14, Antalya, Turkey) focused on full span heat transfer of a smooth airfoil and surface roughness effects on the endwall, in this work further measurements at the airfoil midspan with different deterministic surface roughness are considered. Part I investigates the external heat transfer enhancement due to rough surfaces, whereas part II focuses on surface roughness effects on aerodynamic losses. A set of different arrays of deterministic roughness is investigated in these experiments, varying the height and eccentricity of the roughness elements, showing the combined influence of roughness height and anisotropy of the rough surfaces on laminar to turbulent transition and the turbulent boundary layer as well as boundary layer separation on the pressure and suction side. It is shown that, besides the known effect of roughness height, eccentricity of roughness plays a major role in the onset of transition and the turbulent heat transfer. The experiments are conducted at several freestream turbulence levels (Tu1=1.410.1%) and different Reynolds numbers.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic view of test facility

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Figure 2

Test facility with linear cascade

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Figure 4

Schematic drawing of surface roughness

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Figure 5

Perthometer scan of elliptic surface roughness

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Figure 6

Water cooled airfoil for heat transfer measurements

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Figure 7

Finite element model

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Figure 8

Mach number distribution for Tu1=1.4%(33)

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Figure 9

Acceleration parameter for Tu1=1.4%(33)

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Figure 10

Influence of freestream turbulence on Nusselt number distribution for a smooth surface (33)

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Figure 11

Combined effect of roughness height and eccentricity on external heat transfer at different Re1,c and Tu1

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Figure 12

Effect of eccentricity on turbulent heat transfer

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Figure 13

Roughness induced augmentation of averaged Nusselt number on the suction side at different Re1,c and Tu1

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Figure 14

Roughness induced augmentation of averaged Nusselt number on the pressure side at different Re1,c and Tu1

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Figure 15

Influence of turbulence on suction side heat transfer

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