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

Flow Around a Simplified Car, Part 1: Large Eddy Simulation

[+] Author and Article Information
Siniša Krajnović

Division of Fluid Dynamics, Department of Applied Mechanics, Chalmers University of Technology, SE-412 96 Gothenburg, Swedensinisa@chalmers.se

Lars Davidson

Division of Fluid Dynamics, Department of Applied Mechanics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden

J. Fluids Eng 127(5), 907-918 (May 12, 2005) (12 pages) doi:10.1115/1.1989371 History: Received July 26, 2004; Revised May 12, 2005

Large eddy simulations (LES) were made of flows around a generic ground vehicle with sharp edges at the rear end (an Ahmed body with a 25° angle of the rear slanted surface). Separation of the flow at the rear results in large regions with recirculating flow. As the separation is determined by the geometry, the Reynolds number effects are minimized. Resolution requirements of this recirculating flow are smaller than those in LES of wall attached flows. These two consequences of the geometry of the body are used to predict the experimental flow at relatively high Reynolds number. Recommendations are presented for the preparation and realization of LES for vehicle flows. Comparison of the LES results with the experimental data shows good agreement.

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Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

Time-averaged trace lines on the surface of the front part of the body showing the extensions of the roof vortex, XR, and the lateral vortex, Xs

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Figure 1

Schematic representation of the computational domain with vehicle body. Left: view from the side; right: view from behind the body.

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Figure 2

The computational grid in symmetry plane y=0. D indicates the position of the dummy surface. View from the side of the front part of the body.

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Figure 7

Time-averaged ⟨U⟩t [(a) and (b)] and ⟨W⟩t [(c) and (d)] velocity profiles in the symmetry plane (y=0). Left: slanted surface; right: wake region. Fine grid (solid curve); medium grid (dashed curve); coarse grid (dashed-dotted curve); experiment (symbols).

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Figure 4

Time-averaged streamlines projected onto symmetry plane y=0 of the car body from LES using (a) coarse grid, (b) medium grid, and (c) fine grid. View is from the lateral side of the body.

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Figure 5

Schematic representation of the pressure drag breakdown. CK, CS, and CB are integrated pressure force coefficients from the front, the rear slanted, and the rear vertical surfaces, respectively.

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Figure 6

Distribution of the time-averaged surface pressure coefficients in three planes: y=0, y=0.35H, and y=0.63H. These are plotted along (a) the slanted surface and (b) the rear vertical surface. Fine grid (solid curve); medium grid (dashed curve); coarse grid (dashed-dotted curve); experiment (symbols).

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Figure 8

Time-averaged Reynolds stresses in the symmetry plane (y=0). ⟨uu⟩t [(a) and (b)]; ⟨ww⟩t [(c) and (d)]; ⟨uw⟩t [(e) and (f)]. Left: slanted surface; right: wake region. Fine grid (solid curve); medium grid (dashed curve); coarse grid (dashed-dotted curve); experiment (symbols).

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Figure 9

Time-averaged ⟨U⟩t [(a) and (b)], ⟨V⟩t [(c) and (d)], and ⟨W⟩t [(e) and (f)] velocity profiles in plane y=0.35H. Left: slanted surface; right: wake region. Fine grid (solid curve); medium grid (dashed curve); coarse grid (dashed-dotted curve); experiment (symbols).

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Figure 10

Time-averaged ⟨U⟩t [(a) and (b)], ⟨V⟩t [(c) and (d)], and ⟨W⟩t [(e) and (f)] velocity profiles in plane y=0.63H. Left: slanted surface; right: wake region. Fine grid (solid curve); medium grid (dashed curve); coarse grid (dashed-dotted curve); experiment (symbols).

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Figure 11

Time-averaged turbulent kinetic energy ⟨k¯⟩t in plane y=0.63H. Fine grid (solid curve); medium grid (dashed curve); coarse grid (dashed-dotted curve); experiment (symbols).

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