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Research Papers: Flows in Complex Systems

The Influence of Compressibility on the Aerodynamics of an Inverted Wing in Ground Effect

[+] Author and Article Information
Graham Doig

Tracie J. Barber

 School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW 2031, Australiat.barber@unsw.edu.au

Andrew J. Neely

 School of Engineering and Information Technology, The University of New South Wales at the Australian Defence Force Academy, Canberra, ACT 2600, Australiaa.neely@adfa.edu.au

J. Fluids Eng 133(6), 061102 (Jun 15, 2011) (12 pages) doi:10.1115/1.4004084 History: Received July 03, 2010; Revised April 25, 2011; Published June 15, 2011; Online June 15, 2011

For inverted wings in close ground proximity, such as race car configurations, the aerodynamic ground effect can produce local velocities significantly greater than the freestream and the effects of compressibility may occur sooner than would be expected for a wing that is not close to a ground plane. A three-dimensional computational fluid dynamics study was conducted, involving a modified NASA GA(W)-2 LS [1]-0413 MOD inverted wing with an endplate, to investigate the onset and significance of compressibility for low subsonic Mach numbers. With the wing angle of incidence fixed, Mach numbers from 0.088 to 0.4 were investigated, at ground clearances ranging from infinite (free flight) to a height-to-chord clearance of 0.067. The freestream Mach number at which flow compressibility significantly affects the predicted aerodynamic coefficients was identified to be as low as 0.15. Beyond this point, as the compressible flow conditions around the wing result in changed pressure distribution and separation behavior, treating the flow as incompressible becomes inappropriate and leads to consistent underprediction of lift and drag. The influence on primary vortex behavior of density changes around the wing was found to be relatively inconsequential even at the higher end of the Mach scale investigated. By a freestream Mach number of 0.4 and at low clearances, local supersonic flow regions were established close to the suction peak of the lower wing surface in compressible simulations; the formation of a normal shock wave between the wing and the ground was shown to result in significant increases in separation and therefore overall drag, as well as a distinct loss of downforce.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 8

Turbulence model comparisons to experimental wake profiles at x/c = 1.2, h/c = 0.067

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Figure 9

Incompressible and compressible drag coefficients for decreasing ground clearance and increasing Mach number

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Figure 10

Incompressible and compressible lift coefficients for decreasing ground clearance and increasing Mach number

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Figure 11

Incompressible and compressible moment coefficients for decreasing ground clearance and increasing Mach number

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Figure 12

Incompressible and compressible pressure distributions around the wing at z = 0, h/c = 0.313, ρ/ρ∞ contour plots, and wake profiles at 1.5c, 2c, and 3c from the leading edge for (a) M∞  = 0.15, and (b) M∞  = 0.25

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Figure 13

Incompressible and compressible pressure distributions around the wing at z = 0, h/c = 0.179, ρ/ρ∞ contour plots, and wake profiles at 1.5c, 2c, and 3c from the leading edge for (a) M∞  = 0.15, and (b) M∞  = 0.25

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Figure 14

Incompressible and compressible pressure distributions around the wing at z = 0, h/c = 0.067, ρ/ρ∞ contour plots, and wake profiles at 1.5c, 2c, and 3c from the leading edge for (a) M∞  = 0.15, and (b) M∞  = 0.25

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Figure 15

Incompressible and compressible streamlines around the wing at z = 0, h/c = 0.067

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Figure 16

Lower vortex core paths in the x–y orientation, h/c = 0.179

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Figure 17

Lower vortex core paths in the x–z orientation, h/c = 0.179

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Figure 18

M∞  = 0.4, h/c = 0.179; compressible and incompressible pressure distributions at the semispan, and (inset) region of supersonic flow (dark) under the wing for (a) h/c = 0.313, (b) h/c = 0.179, and (c) h/c = 0.067

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Figure 1

Notation for an inverted wing (section) in ground effect

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Figure 2

(a) An example of the standard mesh for on the wing and symmetry plane (for semispan model), and (b) with the mesh on the endplate and ground (inset: boundary extents on the symmetry plane)

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Figure 3

h/c = 0.179 wing surface pressure distributions at z = 0 for coarse, standard, and fine meshes

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Figure 4

Turbulence model comparisons to experimental pressure distributions, h/c = 0.313

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Figure 5

Turbulence model comparisons to experimental pressure distributions, h/c = 0.179

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Figure 6

Turbulence model comparisons to experimental pressure distributions, h/c = 0.067

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Figure 7

Turbulence model comparisons to experimental lift and drag data (fixed transition cases)

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