Large Eddy Simulation of Transitional Boundary Layers at High Free-Stream Turbulence Intensity and Implications for RANS Modeling

[+] Author and Article Information
Sylvain Lardeau, Michael A. Leschziner

Department of Aeronautics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, UK

Ning Li

Department of Aeronautics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, UKn.li@imperial.ac.uk

J. Turbomach 129(2), 311-317 (Jul 14, 2006) (7 pages) doi:10.1115/1.2436896 History: Received November 15, 2005; Revised July 14, 2006

Large-eddy simulations of transitional flows over a flat plate have been performed for different sets of free-stream-turbulence conditions. Interest focuses, in particular, on the unsteady processes in the boundary layer before transition occurs and as it evolves, the practical context being the flow over low-pressure turbine blades. These considerations are motivated by the wish to study the realism of a RANS-type model designed to return the laminar fluctuation energy observed well upstream of the location at which transition sets in. The assumptions underlying the model are discussed in the light of turbulence-energy budgets deduced from the simulations. It is shown that the pretransitional field is characterized by elongated streaky structures which, notwithstanding their very different structural properties relative to fully established turbulence, lead to the amplification of fluctuations by conventional shear-stress/shear-strain interaction, rather than by pressure diffusion, the latter being the process underpinning the RANS-type transitional model being investigated.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Turbulence energy in blade passage, wake created by a moving rod, T106A blade profile

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Figure 2

Streamwise evolution of the freestream turbulence intensity: (a) comparison between all three cases; and (b) turbulence intensity and intensity of each normal stress for simulation Suu. Symbols represents the theoretical decay of grid turbulence (Eq. 2).

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Figure 3

Contours of the streamwise component of the velocity in the (x,z) plane at y=0.39δ1*, simulation Siso

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Figure 4

Streamwise evolution of the skin-friction coefficient

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Figure 5

(a) Streamwise evolution of the streamwise velocity fluctuations close to the wall (y∕δ1*=0.34); and (b) streamwise evolution of the shear stress

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Figure 6

Streamwise evolution of the ratio −⟨uv⟩∕k at different distance from the wall, (a) simulation Siso and (b) simulation Sfs

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Figure 7

Turbulence-energy budgets (Eq. 3) for the Siso test case

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Figure 8

Turbulence-energy budgets (Eq. 3) for the Sfs test case

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Figure 9

Turbulence-energy budgets (Eq. 3) for the Suu simulation at three streamwise locations

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Figure 10

Anisotropy-invariants map for (a) Siso, (b) Suu, and (c) Sfs simulations




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