Trapped-Vortex in Ground Effect

Garcia, Darwin; Katz, Joseph

doi:10.2514/6.2002-3307

Cited by 8 publications

(8 citation statements)

References 8 publications

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“…Garcia [2] reported similar findings stating that the reduced ground clearance caused the vortices to "untwist" and breakdown for the higher vortex generator angles.…”

Section: Figure 4 -Effect Of Vg Angle On -Cl (Ar=1)supporting

confidence: 56%

“…Comparison to fixed ground data from Garcia [2] shows generally trends are well reproduced but absolute values are not. The exact cause is not clear although Reynold number is slightly mismatched and the Garcia plate has sharp corners and edges so may be producing vortices that are enhancing the lift.…”

Section: Discussionmentioning

confidence: 73%

“…The original tests by Garcia [2] were carried out over a fixed ground plane. Runs were also carried out in this test programme for vortex generator angle of 10 degrees and AR=1 with the moving belt held stationary.…”

Section: Figure 5 -Effect Of Changes In Vg Angle On C D (Ar=1)mentioning

confidence: 99%

“…This type of application has raised challenges in terms of the accuracy of computational simulations when used to aid prediction of vortex trajectory and strength. In order to support fundamental understanding an experimental study by Garcia et al [2] and a numerical simulation by Knight [2] have investigated the characteristics of vortex generated forces on simple flat plates in ground effect fitted with conventional vane vortex generators. This work demonstrated the effectiveness of such configurations in terms of aerodynamic lift (downforce) generation, but the experimental study was carried out over a fixed ground plane which may have a considerable impact on the flow characteristics at small ground clearances.…”

Section: Introductionmentioning

confidence: 99%

“…In the flat plate case the vortex generators act to create reduction in the pressure between the plate and the ground plane. Based on the work of Kuya [1] and Rae [6] counter rotating vortex generators were used by Garcia [2] with two vortex generators either side of a symmetry line at angles of 10, 20 and 30 degrees to the freestream direction. Garcia found the larger vortex generator angles produced stronger vortices and so increased lift coefficient at lower ground clearances.…”

Section: Introductionmentioning

confidence: 99%

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Vortex Induced Aerodynamic Forces on a Flat Plate in Ground Proximity

Holt

Garry

2016

34th AIAA Applied Aerodynamics Conference

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Vehicle underbody longitudinal vortices can have a significant effect on the aerodynamic loads experienced by a body in close ground proximity. A series of wind tunnel tests at a nominal Reynolds number of 2.26 x 10 6 ,were carried out to investigate both (i) the influence of a moving ground plane simulation compared to fixed ground and (ii) the effect of relative location and strength of underbody longitudinal vortices on a simple flat plate, at zero incidence, fitted with vane vortex generators. The presence of vortices between the plate and the ground plane serve to reduce the local pressure and generate a negative lift on the plate. The data indicate that an increase in vortex strength (proportional to an increase in vane vortex generator angle, β) increases plate negative-lift coefficient (C L . The lift coefficient becomes more negative with decreasing ground clearance (h/c) for all cases except those for which there is evidence of vortex breakdown (high vane angles and low ground clearance). The variation of negative-lift-to-drag coefficient ratio shows that the overall aerodynamic efficiency is greater for smaller vortex generator angles atthe lowest ground clearances. The pitching moment coefficient was found to change from nose down to nose up as ground proximity reduced indicating a movement in the centre of pressure position towards the plate trailing edge. AR = Aspect ratio (d/H) β = Vortex generator angle (deg) C L = Lift coefficient C D = Drag coefficient C m = Pitching moment coefficient (+ve nose down, reference 30% chord) c = Chord (plate length 1m) d = Vortex generator spacing (mm) D = Drag (N) L = Lift (N) H = Height of vortex generator (25mm) h = vertical distance between plate and ground (m) I = Turbulence Intensity L/D = Lift to Drag Ratio μ = Viscosity (kg/ms) μ t = Turbulent viscosity (kg/ms) y = Lateral distance from plate centre line (m)

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“…Garcia [2] reported similar findings stating that the reduced ground clearance caused the vortices to "untwist" and breakdown for the higher vortex generator angles.…”

Section: Figure 4 -Effect Of Vg Angle On -Cl (Ar=1)supporting

confidence: 56%

Section: Discussionmentioning

confidence: 73%

Section: Figure 5 -Effect Of Changes In Vg Angle On C D (Ar=1)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Vortex Induced Aerodynamic Forces on a Flat Plate in Ground Proximity

Holt

Garry

2016

34th AIAA Applied Aerodynamics Conference

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Automotive Application of Vortex Generators in Ground Effect

Wijdeven

Katz

2013

Journal of Fluids Engineering

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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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Aerodynamics of a Convex Bump on a Ground-Effect Diffuser

Ehirim

Knowles

Saddington

et al. 2018

Journal of Fluids Engineering

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A ground-effect diffuser is an upward-sloping section of the underbody of a racing car that enhances aerodynamic performance by increasing the downforce, thus improving tire grip. The downforce generated by a diffuser can be increased by geometric modifications that facilitate passive flow control. Here, we modified a bluff body equipped with a 17deg diffuser ramp surface (the baseline/plane diffuser) to introduce a convex bump near the end of the ramp surface. The flow features, force, and surface pressure measurements determined in wind-tunnel experiments agreed with previous studies but the bump favorably altered the overall diffuser pressure recovery curve by increasing the flow velocity near the diffuser exit. This resulted in a static pressure drop near the diffuser exit followed by an increase to freestream static pressure, thus increasing the downforce across most of the ride heights we tested. We observed a maximum 4.9% increase in downforce when the modified diffuser was compared to the plane diffuser. The downforce increment declined as the ride height was gradually reduced to the low-downforce diffuser flow regime.

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Trapped-Vortex in Ground Effect

Cited by 8 publications

References 8 publications

Vortex Induced Aerodynamic Forces on a Flat Plate in Ground Proximity

Vortex Induced Aerodynamic Forces on a Flat Plate in Ground Proximity

Automotive Application of Vortex Generators in Ground Effect

Aerodynamics of a Convex Bump on a Ground-Effect Diffuser

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