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Research Papers

Predicting Rough Wall Heat Transfer and Skin Friction in Transitional Boundary Layers—A New Correlation for Bypass Transition Onset

[+] Author and Article Information
M. Lorenz

e-mail: Marco.Lorenz@kit.edu

A. Schulz

e-mail: Achmed.Schulz@kit.edu

H.-J. Bauer

e-mail: Hans-Joerg.Bauer@kit.edu
Institut für Thermische Strömungsmaschinen,
Karlsruhe Institute of Technology (KIT),
Kaiserstr. 12,
76131 Karlsruhe, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 29, 2012; final manuscript received August 27, 2012; published online June 5, 2013. Assoc. Editor: David Wisler.

J. Turbomach 135(4), 041021 (Jun 05, 2013) (11 pages) Paper No: TURBO-12-1159; doi: 10.1115/1.4007611 History: Received July 29, 2012; Revised August 27, 2012

This paper summarizes the experimental results of a comprehensive study on the heat transfer and aerodynamic losses of a highly loaded turbine blade with surface roughness. A few hundred test cases conducted at several Reynolds numbers, freestream turbulence levels, and different deterministic roughness geometry have been examined. Some of these results have been published in two previous papers, showing a strong effect of roughness on laminar-turbulent bypass transition on the airfoil suction side. Beside roughness height, roughness anisotropy has turned out to be one of the major influencing factors. The airfoil heat transfer distribution of these measurements is used for detecting the transition onset. Additionally, further transition onset data from the literature is reevaluated. Thus, important roughness (geometry) parameters are identified and a new correlation for the transition onset is deduced, including roughness parameters along with freestream turbulence. Moreover, a method to extract the relevant roughness parameters from realistic surface roughness is presented. Additional heat transfer and aerodynamic measurements are conducted for two different real surface roughness types. Calculations with a 2D-boundary layer code on these surfaces are presented in order to validate the new model.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic drawing of surface roughness

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Fig. 3

Discrete element model for turbulent boundary layer modeling on rough surfaces [7]

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Fig. 4

Influence of the roughness density

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Fig. 5

Influence of the roughness eccentricity

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Fig. 6

Transition onset Reynolds number for rough surfaces (Eq. (14))

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Fig. 7

Comparison of correlation to the measured data

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Fig. 8

Roughness height effect on heat transfer [13]

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Fig. 9

Eccentricity effect on heat transfer [13]

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Fig. 10

Roughness data for surface 1

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Fig. 11

Roughness data for surface 2

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Fig. 12

Roughness parameters for the real surface roughness

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Fig. 17

Comparison of the measured and calculated momentum thickness at the trailing edge

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Fig. 16

Comparison of the measured and calculated average heat transfer

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Fig. 15

Comparison of the measured and calculated heat transfer for surface 2

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Fig. 14

Comparison of the measured and calculated heat transfer for surface 1

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Fig. 13

Roughness diameters for surface 1: (a) measured at y = 0, and (b) approximated by elliptical shapes

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