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Special Section Articles

Three-Dimensional Turbulent Vortex Shedding From a Surface-Mounted Square Cylinder: Predictions With Large-Eddy Simulations and URANS

[+] Author and Article Information
B. A. Younis

Department of Civil & Environmental Engineering,
University of California,
Davis, CA 95616
e-mail: bayounis@ucdavis.edu

A. Abrishamchi

Department of Civil & Environmental Engineering,
University of California,
Davis, CA 95616

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received December 11, 2012; final manuscript received August 9, 2013; published online April 28, 2014. Assoc. Editor: Ye Zhou.

J. Fluids Eng 136(6), 060907 (Apr 28, 2014) (10 pages) Paper No: FE-12-1628; doi: 10.1115/1.4025254 History: Received December 11, 2012; Revised August 09, 2013

The paper reports on the prediction of the turbulent flow field around a three-dimensional, surface mounted, square-sectioned cylinder at Reynolds numbers in the range 104–105. The effects of turbulence are accounted for in two different ways: by performing large-eddy simulations (LES) with a Smagorinsky model for the subgrid-scale motions and by solving the unsteady form of the Reynolds-averaged Navier–Stokes equations (URANS) together with a turbulence model to determine the resulting Reynolds stresses. The turbulence model used is a two-equation, eddy-viscosity closure that incorporates a term designed to account for the interactions between the organized mean-flow periodicity and the random turbulent motions. Comparisons with experimental data show that the two approaches yield results that are generally comparable and in good accord with the experimental data. The main conclusion of this work is that the URANS approach, which is considerably less demanding in terms of computer resources than LES, can reliably be used for the prediction of unsteady separated flows provided that the effects of organized mean-flow unsteadiness on the turbulence are properly accounted for in the turbulence model.

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References

Figures

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Fig. 1

Geometry, computational domain, and dimensions

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Fig. 2

Close-up of mesh in x-y plane

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Fig. 3

Predicted drag (a) and lift (b) coefficients with standard and modified k-ε models (Re = 105)

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Fig. 5

Predicted CD (left) and CL (right) at different Re: (a), (b) LES (5 × 104); (c), (d) modified k-ε (5 × 104); (e), (f) LES (105); and (g), (h) modified k-ε (105)

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Fig. 6

Energy spectrum for Re = 5 × 104 (left) and 105 (right). Standard and modified k-ε models (top and middle rows), LES (bottom row).

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Fig. 7

Vertical section of cylinder showing force monitoring locations A, B, and C

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Fig. 8

Drag (top) and lift (bottom) coefficients at monitoring locations. Predictions with modified k-ε model (Re = 105).

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Fig. 9

Drag (top) and lift (bottom) coefficients at monitoring locations. Predictions with LES (Re = 105).

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Fig. 10

Modified k-ε predictions of the pressure contours (Pa) at different phase angles (Re = 105)

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Fig. 11

Predicted velocity vectors (m/s) for Re = 104 (left column) and 105 (right column) with standard and modified k-ε models and LES

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Fig. 12

Dependence of eddy viscosity on phase angle as predicted with the modified k-ε model. Results shown are at z/D = 1.8 (Re = 105).

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Fig. 13

Modified k-ε model results for the vertical component of vorticity (Re = 105)

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Fig. 4

Predicted and measured variation with Re of the average and rms CL and CD and the Strouhal number

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