Research Papers: Flows in Complex Systems

Numerical Investigation of Crossflow Separation on the A-Pillar of a Passenger Car

[+] Author and Article Information
Sabine Bonitz

Vehicle Engineering and Autonomous Systems,
Department of Mechanics and
Maritime Sciences,
Chalmers University of Technology,
Gothenburg 41296, Sweden
e-mail: sabine.bonitz@chalmers.se

Lars Larsson

Marine Technology,
Department of Mechanics and
Maritime Sciences,
Chalmers University of Technology,
Gothenburg 41296, Sweden
e-mail: lars.larsson@chalmers.se

Lennart Löfdahl

Vehicle Engineering and Autonomous Systems,
Department of Mechanics and
Maritime Sciences,
Chalmers University of Technology,
Gothenburg 41296, Sweden

Simone Sebben

Vehicle Engineering and Autonomous Systems,
Department of Mechanics and
Maritime Sciences,
Chalmers University of Technology,
Gothenburg 41296, Sweden

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 24, 2017; final manuscript received April 18, 2018; published online June 4, 2018. Assoc. Editor: Ning Zhang.

J. Fluids Eng 140(11), 111105 (Jun 04, 2018) (9 pages) Paper No: FE-17-1684; doi: 10.1115/1.4040107 History: Received October 24, 2017; Revised April 18, 2018

The flow around passenger cars is characterized by many different separation structures, typically leading to vortices and areas of reversed flow. The flow phenomena in these patches show a strong interaction and the evolution of flow structures is difficult to understand from a physical point of view. Analyzing surface properties, such as pressure, vorticity, or shear stress, helps to identify different phenomena, but still it is not well understood how these are created. This paper investigates the crossflow separation (CFS) on the A-pillar of a passenger car using numerical simulations. It is discussed how the CFS and the resulting A-pillar vortex can be identified as well as how it is created. Additionally, the vortex strength is determined by its circulation to understand and discuss how the vortex preserves until it merges with the rear wake of the vehicle.

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Fig. 1

Types of singular points—node, focus, and saddle point

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Fig. 2

Defined coordinate system and locations of crossplanes used in the discussion

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Fig. 3

Refinement boxes around the car

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Fig. 4

X-vorticity distribution with limiting streamlines for three different mesh configurations: (a) y > 30, (b) y < 5, and (c) y < 1

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Fig. 5

Schematic 2D sketch of the vorticity and wall shear stress lines along a crossflow separation

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Fig. 6

Limiting streamlines along the A-pillar; surface colored by vorticity magnitude

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Fig. 7

Perspective view on four different crossplanes (A, B, C, and H) along and downstream the A-pillar; colored by vorticity magnitude and showing 2D streamlines in the crossplanes

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Fig. 8

A-pillar vortex visualized by the Q criterion isosurface Q = 0 and colored by the x-vorticity

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Fig. 9

Perspective view on four different crossplanes (D, E, F, and G); colored by vorticity magnitude and showing 2D streamlines in the crossplanes

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Fig. 10

x-Vorticity along the A-pillar

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Fig. 11

Vorticity components along a CFS

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Fig. 12

Schematic 2D sketch of two surface vorticity scenarios: (a) schematic 2D sketch of surface vorticity of equal magnitude and (b) schematic 2D sketch of surface vorticity of unequal magnitude

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Fig. 13

Three-dimensional streamlines going through the A-pillar vortex in plane G and their upstream and downstream

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Fig. 14

Circulation and area along the A-pillar vortex; position based on normalized vehicle length development

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Fig. 15

Normalized crossflow velocity at the A-pillar in plane C (looking in the downstream direction)



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