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Research Papers: Fundamental Issues and Canonical Flows

Large-Scale Vortex Generation Modeling

[+] Author and Article Information
Christopher D. Booker, Xin Zhang

 School of Engineering Sciences, University of Southampton, Southampton, SO17 1BJ, UK

Sergei I. Chernyshenko

Department of Aeronautics,  Imperial College London, South Kensington Campus, London SW7 2AZ, UK

J. Fluids Eng 133(12), 121201 (Dec 19, 2011) (16 pages) doi:10.1115/1.4005314 History: Revised October 13, 2011; Received November 25, 2011; Published December 19, 2011; Online December 19, 2011

Methods of modeling vortex generation in computational fluid dynamics calculations without meshing the vortex generating device are investigated. In this way, the effect of adding vortices to existing flows can be assessed without the need to modify the computational grid; this can represent a significant saving. Previous work in this area has focused on boundary layer control. This study looks at larger scale applications, such as using vortices for force augmentation or directing flow. Two different approaches are used: modeling the vortex generator and modeling just the vortex alone. For the former, an existing method, which acts to align the flow with the vortex generator by adding a forcing term to the governing equations, is tested, but found to be unsuitable for use on this scale. The other approach is to add specified vortex velocity profiles, allowing the introduction of arbitrary vortices. A new version is developed to add continuous 3D velocity distributions in regions where desired vortices are to be created. It is implemented using several different forms of forcing. After basic testing, all methods are applied in a practical engineering case using a commercial solver.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Examples of “large-scale” VGs on racing cars. (A): VGs on the underside of a 2000 Lola Champ Car. These create vortices under the car which increase the downforce on it due to their low pressure, and are the kind investigated by Katz [2-3,12-14]. (B): The lower edge of a Formula One bargeboard generates a similar vortex. Here the top edge is serrated to produce several vortices (Honda RA108). (C): VGs just ahead of the top of the sidepod (Force India VJM03). (D): VGs on the inboard side of front-wing end-plates (Honda RA108).

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Figure 2

Illustration of cylindrical polar coordinate notation

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Figure 3

Notation used in the BAY modeling approach. The VG to be modeled is shaded.

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Figure 4

Previous approaches to cell selection for VG modeling methods. After Iannelli [21].

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Figure 5

Sections of the grids with VG and the “equivalent grid” used for the modeling method, with selected cells shaded

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Figure 6

Comparison of meshed and modeled VGs at 10 ° and 25 °. An isosurface of Q=100,000 is shown, shaded by ux/u∞ (the legend applies to all contours). The black line represents the vortex cores as identified using eigenmode analysis.

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Figure 7

Comparison of vortex tangential and axial velocity profiles one chord-length downstream of the VG given by meshed VGs and BAY modeling

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Figure 8

Pressure on the surface (y = 0) and close to the height of the vortex (y=0.8b, where b is the VG span) around meshed and modeled VGs. The black line shows vortex cores identified using eigenmode analysis.

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Figure 9

Sketch of the velocity profile modeling approach, illustrating some of the notation

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Figure 10

Convergence of error in setting the velocity using different forcing approaches for a simple test case over the first 100 iterations

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Figure 11

Example velocity, pressure and force fields calculated from the Navier-Stokes equations for the simple case of adding an axisymmetric q-vortex to a uniform flow. The bottom right plot shows the effect of varying uχ|axis on the axial force distribution.

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Figure 12

The engineering case used to test the methods

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Figure 13

Details of the engineering case. The strake that is not included in the modeling grids is shaded. The black lines indicate the extents of the cylindrical region and the plane used to display results in Figs.  1415.

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Figure 14

Changes in velocity from the case without the strake on a plane 1rc downstream of the end of the strake

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Figure 15

Changes in pressure from the case without the strake on a plane 1rc downstream of the end of the strake

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Figure 16

Convergence of error in setting the velocity using different forcing approaches for an engineering case over the first 100 iterations

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Figure 17

Changes in tangential velocity using profile-based modeling approaches, on a plane at the downstream end of the source term region, relative to the desired peak tangential velocity

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Figure 18

Changes in axial velocity using profile-based modeling approaches, on a plane at the downstream end of the source term region, relative to the magnitude of the desired axial velocity at the axis

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