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TECHNICAL PAPERS

Unsteady Numerical Simulations of Turbulence and Coherent Structures in Axial Flow Near a Narrow Gap

[+] Author and Article Information
D. Chang

Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

S. Tavoularis1

Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario K1N 6N5, Canadatav@eng.uottawa.ca

1

Corresponding author.

J. Fluids Eng 127(3), 458-466 (Feb 03, 2005) (9 pages) doi:10.1115/1.1900140 History: Received November 11, 2004; Revised February 03, 2005

Axial flow in a rectangular channel containing a cylindrical rod has been simulated numerically by solving the unsteady Reynolds-averaged Navier–Stokes equations with a Reynolds stress model. The time- and phase-averaged mean velocity and turbulent stresses are in fair agreement with previous experimental results in a similar configuration. The study further documents the formation of quasi-periodic coherent structures in the form of vortex pairs and the important role that they play in transporting fluid across the gap region.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketches of (a) the computational geometry and (b) the computational mesh on the y-z plane, also showing details in the gap region and near the bottom wall

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Figure 2

Variation of the time-averaged streamwise velocity at z∕D=1, x∕D=10, near the bottom wall (∎: case 1; –: case 2, ◆: case 3, ▴: case 4)

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Figure 3

(a) Isocontours of the time-averaged dimensionless axial velocity U¯∕Ub in the GT experiments (12) (left) and the present simulations (right) (b) vector plots of the time-averaged velocity component (left) and projected streamlines (right) on a cross-sectional plane in the present simulations

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Figure 4

Isocontours of time-averaged, nondimensionalized GT measurements (12) (left) and present simulations (right): (a) axial rms velocity fluctuation u′∕Ub; (b) transverse rms velocity fluctuation v′∕Ub; (c) spanwise rms velocity fluctuation w′∕Ub; and (d) turbulent kinetic energy k¯∕Ub2

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Figure 5

Isocontours of time-averaged, nondimensionalized GT measurements (12) (left) and present simulations (right): (a) Transverse turbulent shear stress uv¯∕Ub2; and (b) dimensionless spanwise turbulent shear stress uw¯∕Ub2; (c) dimensionless axial turbulent shear stress vw¯∕Ub2; (d) dimensionless transverse turbulent shear stress coefficient uv¯∕u′v′; (e) dimensionless spanwise turbulent shear stress coefficient uw¯∕u′w′; (f) dimensionless axial turbulent shear stress coefficient vw¯∕v′w′

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Figure 6

Predicted isocontours of the percent ratio of the coherent components to the totals: (a) Streamwise rms velocity ratio ucoh′¯∕u′¯; (b) transverse rms velocity ratio vcoh′¯∕v′¯; (c) spanwise rms velocity ratio wcoh′¯∕w′¯; and (d) turbulent kinetic energy ratio k¯coh∕k¯

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Figure 7

Comparison of present simulations (open symbols) with experimental results (12) (solid symbols) for total averages (◻, ∎) and coherent (▵, ▴) parts on the equidistant plane: (a) Streamwise normal stress; (b) transverse normal stress; (c) spanwise normal stress; the simulation results have been connected by solid lines as an aid to the eye.

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Figure 8

Coherent structures identified by the Q criterion; the section shown is 20 D long

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Figure 9

Predicted isocontours on the equidistant plane of: (a) The dimensionless instantaneous static pressure P∕(1∕2ρUb2); (b) the dimensionless instantaneous spanwise velocity W∕Ub; and (c) instantaneous streamlines; coherent structures identified by the Q criterion are also shown in all plots; all plots are 7.2 D long and 3 D high

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Figure 10

Experimental (left) and simulated (right) surface streamlines of velocity fields as seen by an observer moving with the average convective speed of the coherent structures

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Figure 11

(a) Representative time histories of the spanwise velocity in the centre of the gap: present simulations (—) and experimental results (----); (b) the power spectrum, in arbitrary logarithmic scale, of the time history of the simulated spanwise velocity in the center of the gap

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