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Research Papers: Flows in Complex Systems

Automotive Application of Vortex Generators in Ground Effect

[+] Author and Article Information
Trebsijg van de Wijdeven

Visiting SDSU
Mechanical, Maritime and Materials Engineering,
Delft University of Technology,
Delft, The Netherlands

Joseph Katz

Professor of Aerospace Engineering,
San Diego State University,
San Diego, CA 92182

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 13, 2013; final manuscript received October 30, 2013; published online December 2, 2013. Assoc. Editor: Zvi Rusak.

J. Fluids Eng 136(2), 021102 (Dec 02, 2013) (8 pages) Paper No: FE-13-1373; doi: 10.1115/1.4025917 History: Received June 13, 2013; Revised October 30, 2013

Vortex generators (VG) are widely used in the aerospace industry, mainly to control boundary layer transition and to delay flow separations. A different type of VG is used on race cars for manipulating the flow over and under the vehicle, mainly to generate downforce (which is needed for better performance). Contrary to the VGs used on airplanes' wings, the VGs discussed here are much taller than the local boundary layer thickness and are not intended to control laminar to turbulent flow transition. Although, the effect of such VGs was studied in the past, not all features of the flow fields were documented. For example, the shape of the vortex wake behind a VG, the wake rollup and the resulting pressure signature is still not well understood. Consequently, this study investigates the above questions by using experimental methods. A generic model with several VGs was tested in a low speed wind tunnel and in addition to the lift and drag the surface pressure distribution and the trailing vortex signature behind the VGs were studied. In order to demonstrate the incremental effect of the vortex wake, airfoil shaped VGs were also tested, mainly to quantify the “blockage effect” between the plate and the ground plane. The effect of rake (vehicle's angle of attack), which was not documented in previous work, was also investigated here. The results of this study provide quantitative information on the expected loads and pressure distribution behind such large-scale VGs; data needed for the successful application of such devices to actual vehicles.

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References

Figures

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Fig. 1

Typical positioning of VGs on a race car (a) and on a road vehicle (b) behind the front axle

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Fig. 2

Geometry and dimensions of the model tested. Note the four rectangular VGs on this model. Dimensions are in inches, and metric units are in parentheses.

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Fig. 3

Schematic description of the experimental apparatus (which was also described in Ref. 4). The rear strut's length could be changed remotely to vary the model (lower plate) angle of attack.

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Fig. 4

Computational model used to estimate wind tunnel corrections

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Fig. 5

Comparison of lift and drag coefficients with previous results of Ref. [4] (h is ground clearance and c is the plate's chord). Uncertainty in CL is ±0.015 and in CD is ±0.010.

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Fig. 6

The NACA 0012 shape VGs, which were used instead of the flat-plate shaped VGs

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Fig. 7

Lift and drag coefficient versus ground clearance for the airfoil shaped VGs. Uncertainty in CL is ±0.015 and in CD is ±0.010.

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Fig. 8

Comparison of the forces, between one and two VGs per side. Uncertainty in CL is ±0.015 and in CD is ±0.010.

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Fig. 9

Schematic description of trailing vortices core positions behind the VGs at h/c = 0.0533

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Fig. 10

Typical pressure coefficient distribution (Cp) behind the VGs for three ground clearance values

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Fig. 11

Pressure distribution at station x/c = 0.30 for three ground clearance values. Uncertainty in CP is ±0.001.

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Fig. 12

Pressure distribution at station x/c = 0.63 for three ground clearance values. Uncertainty in CP is ±0.001.

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Fig. 13

Pressure distribution at station x/c = 0.90 for three ground clearance values. Uncertainty in CP is ±0.001.

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Fig. 14

Effect of pitch angle on the lift coefficient. Definition of pitch angle is on top of this figure. Uncertainty in CL is ±0.015 and in CD is ±0.010. Note that the data here represents the net effect of the VGs (the effect of the plate at an angle of attack was subtracted with the tares).

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Fig. 15

Effect of pitch angle on the lift and drag coefficients. Uncertainty in CL is ±0.015 and in CD is ±0.010. Note that the data here represents the net effect of the VGs (the effect of the plate at an angle of attack was subtracted with the tares). Also, negative pitch is nose down for an actual vehicle!

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Fig. 16

Typical pressure coefficient (Cp) distribution behind the VGs for three angles of attack

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Fig. 17

Spanwise pressure distribution at station x/c = 0.30 for three pitch angles. Uncertainty in CP is ±0.001.

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Fig. 18

Spanwise pressure distribution at station x/c = 0.63 for three pitch angles. Uncertainty in CP is ±0.001.

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Fig. 19

Spanwise pressure distribution at station x/c = 0.90 for three pitch angles. Uncertainty in CP is ±0.001.

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Fig. 20

Lift coefficient versus angle of attack for the present model (including the forces on the plate) and for several types of race cars. Note that the frontal area is used for the definition of the lift coefficient (only for this figure).

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