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Research Papers: Flows in Complex Systems

# Large Eddy Simulation Investigation of the Hysteresis Effects in the Flow Around an Oscillating Ground Vehicle

[+] Author and Article Information
Siniša Krajnović1

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

Anders Bengtsson

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

Branislav Basara

AVL List GmbH, Advanced Simulation Technologies, A-8010 Graz, Austria

1

Corresponding author.

J. Fluids Eng 133(12), 121103 (Dec 20, 2011) (9 pages) doi:10.1115/1.4005260 History: Received March 24, 2011; Revised October 06, 2011; Published December 20, 2011; Online December 20, 2011

## Abstract

This paper presents large eddy simulations (LES) of flow around a simplified vehicle model oscillating around its vertical axis. The frequency of the Strouhal number St = $0.068$ and a relatively small amplitude of the oscillation are chosen to be representative for the crosswind conditions of vehicles on the road. The results were found to agree well with data from previous experimental investigations. Furthermore, the differences in LES flows between quasi-steady and dynamic flow conditions are presented and underlying flow mechanisms are explored. The cause of the phenomena of hysteresis and phase shift was found in the inertia of the flow to adjust to sudden changes in the direction of the oscillation of the body.

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## Figures

Figure 1

(a)–(c) Geometry of the body. (d) Sketch of the models’ setup in the computational domain.

Figure 2

(a) Sketch of the extreme positions of the oscillating model. The body at position +Δβ and -Δβ is colored with light gray and dark gray, respectively. The computational grid is shown for position β=0 deg. Computational grid for yaw angles (b) β=0 deg and (c) β=10 deg.

Figure 3

Comparison between different computational grids ((a)-(c)) and between the present LES and experimental data ((d)-(f)) of the Cp values at points (a) and (d) P1, (b) and (e) P2, and (c) and (f) P3

Figure 4

Comparison of the (a) drag coefficient Cx, (b) drag coefficient calculated in the Eiffel axis linked to the upstream velocity U∞, Cxo, (c) side force coefficient Cy, and (d) side force coefficient linked to the Eiffel axis Cyo

Figure 5

Second invariant of velocity gradient Q=20000 for yaw angles (a) β=0 deg, (b) β=6 deg, (c) β=10 deg, (d) β=10 deg, (e) β=6 deg, (f) β=0 deg, (g) β=-6 deg, (h) β=-10 deg, (i) β=-10 deg, and (j) β=-6 deg

Figure 6

Iso-surface of the second invariant of the velocity gradient tensor Q=2×104 for position β=10 deg. LES of (a)–(b) quasi-steady flow, (c)–(d) dynamic flow for increasing β, and (e)–(f) dynamic flow for decreasing β.

Figure 7

Iso-surface of the second invariant of the velocity gradient tensor Q=2×104 for position β=0 deg. LES of (a)–(b) quasi-steady flow, (c)–(d) dynamic flow for increasing β, and (e)–(f) dynamic flow for decreasing β.

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