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Research Papers: Flows in Complex Systems

Influence of the Slant Angle of 3D Bluff Bodies on Longitudinal Vortex Formation

[+] Author and Article Information
Patrick Gilliéron

Department of Research, “Fluid Dynamics and Aerodynamics” Team, Renault SA Service 68260, Code API: TCR AVA 058 1, Avenue du Golf, 78288 Guyancourt Cedex, Francepatrick.gillieron@renault.com

Annie Leroy1

Institut PRISME, University of Orleans, 8 rue Leonard de Vinci, F-45072 Orleans Cedex 2, Franceannie.leroy@univ-orleans.fr

Sandrine Aubrun, Pierre Audier

Institut PRISME, University of Orleans, 8 rue Leonard de Vinci, F-45072 Orleans Cedex 2, France

1

Corresponding author.

J. Fluids Eng 132(5), 051104 (May 06, 2010) (9 pages) doi:10.1115/1.4001450 History: Received June 10, 2009; Revised February 16, 2010; Published May 06, 2010; Online May 06, 2010

This paper presents the experimental results and analytical arguments concerning simplified geometries of the rear window and windscreen of automotive vehicles in order to contribute to a better understanding of the swirling structure formation and vortex bursting processes. Static pressure distributions and skin friction line visualizations on both sides of the edge where the swirling structure is generated on the rear window of an Ahmed body are presented for different slant angles. Results show the influence of the slant angle on the swirling structure formation and further show that the vortex bursting process can be promoted by small rear window angles. These results are then extrapolated with the help of analytical demonstrations to the windscreen configuration to demonstrate that large windscreen slopes would have the same disintegration effect.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic representation of windscreen with a slant angle θ

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Figure 2

Ahmed body geometry, from Ref. 7. Slant angle θ of rear window (x0,y0,z0) and (x,y,z): frames linked to the freestream velocity direction and to the left side line of the rear window, respectively

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Figure 3

Schematic representation of amount of the windscreen detachment, left back view; the secondary structure is linked to the existence of the principal longitudinal swirling structure

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Figure 4

Schematic representation of the left part of rear window detachment for slant angles θ ranging between 12 deg and 30 deg, according to Refs. 7,9, back view

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Figure 6

Axial velocity profiles: jet and wake profiles

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Figure 7

Composition of azimuthal and freestream velocities Vθ and V0 on the windscreen edge, resulting velocity vector W

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Figure 8

Location of the static pressure tabs on the left side of the rear window. The four lines intersect at P

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Figure 9

Location of the static pressure tabs on the rear window

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Figure 10

Streamline representation along roof and rear window

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Figure 20

Referential system linked to the swirling structure: precession and nutation angles. Azimuthal Vθ and longitudinal VX velocities in a X=Cte plane.

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Figure 17

Angular deviation λ̣ versus the reduced distance from P, x/l, for slant angles θ=15, 20, and 25 deg; V0=30 m s−1

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Figure 18

Ratio between the angular deviation and the slant angle versus the reduced distance from P, x/l, for slant angles θ=15, 20, and 25 deg; V0=30 m s−1

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Figure 19

(a) Slant angle and angular deviation of the lateral friction line λ; (b) friction line visualizations on the side of the rear window, θ=15 deg, V0=30 m s−1; (c) friction line visualizations on the side of the rear window, θ=20 deg, V0=30 m s−1; (d) friction line visualizations on the side of the rear window, θ=25 deg, V0=30 m s−1

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Figure 5

Composition of azimuthal and freestream velocities Vθ and V0 on the rear window, resulting velocity vector W; (X,Y,Z): coordinate system linked to the swirling structure axis

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Figure 11

Static pressure coefficient distribution on the side of the rear window (left) and on the rear window (right)

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Figure 12

Normal and tangential components of the flow velocity on the windscreen near the separation geometrical edge

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Figure 13

Static pressure coefficients Cp along the lines D1, D2, D3, and D4 on the side of the rear window, V0=30 m s−1

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Figure 14

Radial static pressure coefficient gradients along the lines D1, D2, D3, and D4; θ=25° and V0=30 m s−1

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Figure 15

Static pressure coefficients Cp along the lines DL and D4, V0=30 m s−1

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Figure 16

Difference in static pressure coefficients along the lines D4 and DL: ΔCp=Cp∣D4−Cp∣DL and V0=30 m s−1

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Figure 21

Evolution of the ratio of azimuthal Vθ and longitudinal VX velocities as a function of the deviation angle λ

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