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SPECIAL SECTION ON RANS/LES/DES/DNS: THE FUTURE PROSPECTS OF TURBULENCE MODELING

Comparative LES and Unsteady RANS Computations for a Periodically-Perturbed Separated Flow Over a Backward-Facing Step

[+] Author and Article Information
A. Dejoan

Department of Aeronautics, Imperial College London, London SW7 2AZ, UK.a.dejoan@imperial.ac.uk

Y.-J. Jang

Department of Aeronautics, Imperial College London, London SW7 2AZ, UK.

M. A. Leschziner

Department of Aeronautics, Imperial College London, London SW7 2AZ, UK.mike.leschziner@imperial.ac.uk

J. Fluids Eng 127(5), 872-878 (Mar 16, 2005) (7 pages) doi:10.1115/1.2033012 History: Received July 22, 2004; Revised March 16, 2005

Large eddy simulation and statistical turbulence closures are used to investigate and contrast the ability of both strategies to represent the effects arising from the unsteady perturbation of a separated backward-facing-step flow caused by a slot jet injected periodically at zero net mass-flow rate into the flow at the step edge, at an angle of 45 deg relative to the flow direction. Experimental data show the effects to depend nonlinearly on the perturbation frequency, the strongest response arising at a Strouhal number of 0.2, which is the condition investigated herein. The principal response is a shortening of the separation bubble by almost 30%, a result that is highly pertinent to active flow control. As the injection frequency lies within the low-frequency range of the large scales of the turbulence spectrum, an issue of particular interest that is addressed herein is the ability of the statistical models, operating within a phase-averaged URANS framework, to reproduce the experimental observations and the response derived from the simulation.

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Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

The flow configuration

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Figure 2

Autocorrelation coefficient of the streamwise velocity fluctuations in the spanwise direction at different locations x∕h, from the LES of the unperturbed flow

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Figure 3

Ratio of the Kolmogorov length scale to the grid length scale, from the LES of the unperturbed flow

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Figure 4

Energy spectra of the streamwise velocity fluctuation, from the LES of the unperturbed flow

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Figure 5

Velocity and streamwise normal-stress profiles, from the LES of the unperturbed flow performed with two grid resolutions

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Figure 6

Profiles of normal-stress components above the step corner, from the LES of the unperturbed flow performed with two grid resolutions. Comparison with Moser ’s DNS data (16) (Rτ=180, i.e., Re=3250).

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Figure 7

Time-averaged streamfunction contours; unperturbed and perturbed flows

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Figure 8

Skin-friction coefficient at the bottom wall downstream of the step; unperturbed and perturbed flows

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Figure 9

Time-averaged streamwise-velocity profiles; unperturbed and perturbed flows

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Figure 10

Time-averaged profiles of the Reynolds shear stress; unperturbed and perturbed flows

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Figure 11

Time-averaged modeled and resolved Reynolds shear stress at the location x∕h=0.36; perturbed flow, (AJL-ε) model

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Figure 12

Phase-averaged streamlines contours at the phase angles Φ=0,π∕2,π,3π∕2; perturbed flow

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Figure 13

Phase-averaged Reynolds shear stress along the streamwise direction at the locations y∕h=−0.2, perturbed flow

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