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Research Papers: Flows in Complex Systems

Numerical Implementation of Detached-Eddy Simulation on a Passenger Vehicle and Some Experimental Correlation

[+] Author and Article Information
L. Sterken

Department of Applied Mechanics,
Chalmers University,
Hörsalsvägen 7a,
Göteborg 41258, Sweden;
Volvo Car Group,
Aerodynamics, 91760,
Göteborg 40531, Sweden
e-mail: Lennert.sterken@volvocars.com

S. Sebben

Department of Applied Mechanics,
Chalmers University,
Hörsalsvägen 7a,
Göteborg 41258, Sweden;
Volvo Car Group,
Aerodynamics, 91760,
Göteborg 40531, Sweden

L. Löfdahl

Department of Applied Mechanics,
Chalmers University,
Hörsalsvägen 7a,
Göteborg 41258, Sweden

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 9, 2015; final manuscript received March 18, 2016; published online June 3, 2016. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 138(9), 091105 (Jun 03, 2016) (14 pages) Paper No: FE-15-1253; doi: 10.1115/1.4033296 History: Received April 09, 2015; Revised March 18, 2016

This study presents an implementation of delayed detached-eddy simulation (DDES) on a full-scale passenger vehicle for three configurations with the use of commercial software harpoon (mesher) and ansys fluent (solver). The methodology aims to simulate the flow accurately around complex geometries at relevantly high Re numbers for use in industrial applications, within an acceptable computational time. Geometric differences between the three configurations ensure significant drag changes that have a strong effect on the wake formation behind the vehicle. Therefore, this paper focuses on the analysis of the base wake region. At first, the paper evaluates the performance of the DDES, where it verifies the different operating conditions of the flow around the vehicle with respect to the DDES definition. In a second step, the numerical results are correlated with force measurements and time-averaged flow field investigations, conducted in the Volvo Cars aerodynamic wind tunnel (WT). The comparison confirms a good agreement between the experiments and the simulations. The resolved flow scales obtained by DDES give a further insight into differences in the wake flow characteristics between the configurations related to their contribution to drag.

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Figures

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Fig. 1

Ring vortex behind squareback vehicle, created with an isosurface of cp = −0.22

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Fig. 2

Geometrical representation

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Fig. 3

Configurational changes: (a) improved underbody and (b) steplight cover and 0.25 m extensions

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Fig. 4

Vehicle positioning in the numerical WT

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Fig. 5

WT moving-ground system [27]

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Fig. 6

Overview of pressure measurements: (a) main base region, (b) lamp positions, and (c) traversing unit

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Fig. 7

Plane visualization

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Fig. 8

DDES-performance analysis: DES-limiter fd at symmetry plane near the rear-end of the vehicle

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Fig. 9

DDES-performance analysis: νt/ν at symmetry plane

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Fig. 10

DDES-performance analysis: (a) kmod symmetry plane, (b) kres symmetry plane, (c) kmodz plane through wheel centers, and (d) kresz plane through wheel centers

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Fig. 11

CFL number at symmetry plane: (a) Δt = 0.0002 and (b) Δt = 0.0001

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Fig. 12

Force coefficient CD, CLF, and CLR: (a) time history superimposed with runnning average and (b) running average

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Fig. 13

Statistical error

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Fig. 14

Running standard deviation: (a) force coefficients and (b) running average of force coefficients

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Fig. 15

Pressure distribution of base region for WT (left) and CFD (right): ((a) and (b)) configuration 1, ((c) and (d)) configuration 2, and ((e) and (f)) configuration 3

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Fig. 16

Pressure distribution over symmetry line: (a) cp and (bcp

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Fig. 17

Local drag superimposed with cptot-contour lines: (a) transverse plane WT, (b) symmetry plane WT, (c) transverse plane CFD, and (d) symmetry plane CFD

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Fig. 18

Velocity streamlines in the wake behind vehicle for the symmetry plane (left) and a plane at z = 0.747 m (right): ((a) and (b)) configuration 1, ((c) and (d)) configuration 2, and ((e) and (f)) configuration 3

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Fig. 19

Local drag superimposed with streamlines for configuration 1: (a) time-averaged and (b) instationary instant

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Fig. 20

kres at the symmetry plane (left) and z plane at z = 0.824 m (right): ((a) and (b)) reference, ((c) and (d)) improved underbody, and ((e) and (f)) rear-end extensions

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Fig. 21

Isosurface plots of kres = 0.06: (a) reference, (b) improved underbody, and (c) rear-end extensions

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Fig. 22

Normalized turbulent stresses at the symmetry plane for u′2¯/U∞2 (left), ν′2¯/U∞2 (middle), and w′2¯/U∞2 (right): ((a)–(c)) configuration 1, ((d)–(f)) configuration 2, and ((g)–(i)) configuration 3

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