Motorsport Aerodynamics

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Motorsport Aerodynamics
Brian Feldman

• Jamie
• Arner

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Importance of Aerodynamics
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Aerodynamic Design Methodology

• CFD
• Develop parts and visualize flow over car and
  devices before models are built
• Wind Tunnel
• Scale model testing of devices
• Full size testing of vehicle (rolling road)
• Track
• Devices are assessed and approved for racing

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Motorsports

• Highly Developed
• Highly Secretive

• Heavily Regulated
• Extremely Competitive

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Front Air Dam
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• Limits the Amount of Air Passing Underneath the
  Car
• Contributes to High Pressure In Front of the Car
• Causes Low Pressure Underneath the Car

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Front Splitter
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Captures Some of the High Pressure Created In
Front of the Air Dam, Causing Downforce
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Side Skirts
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• Side Skirts Prevent High Pressure Air Around the
  Car from
• Disturbing the Low Pressure Underneath the Car

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Canards (French for Duck)

• Captures a Small Amount
• of Downforce by Redirecting
• Airflow Upward.
• Main Purpose is the
• Creation of Large Vortices
• That Run the Length of
• the Vehicle

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Canard Vortices
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• Vortices Spin Inwards, Towards the Vehicle on
  Each Side
• Canard Vortices Work In Conjunction With Side
  Skirts to Limit the High Pressure Air From Mixing
  With the Low Pressure Air Found Underneath the Car

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Venturi Tunnels / Rear Diffusers
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Ground Effects

• Ride Height
• Downforce Increases
• with Reduced Clearance h
• Diffuser Stall
• Individual to Each Design

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Underbody Pressure
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• Suction Peak Occurs Near the Diffuser Entrance
• Can be used to Control the Vehicle Center of
  Pressure

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Rear Diffuser

• Expands Air Back Down
• to Road Velocity
• Slows the Flow and Raises
• the Air Pressure
• Acts as a Pump Drawing
• More Air from the Undertray
• Rear Wing Drives the
• Diffuser Because of its Proximity to the
  Wing's Low Pressure Side
• Reduce the Overall Pressure Drag on the Vehicle
  by Introducing High Pressure Air into the Low
  Pressure Wake Region

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Diffuser Vortices

• Two Vortices form at the Side Edges
• of the Diffuser
• Flow Separates at the Sharp Leading Edge
• Reattached by the Side Vortices
• Separation Line is Dictated by the Leading Edge
• Reynolds Number Effect Insignificant
• Reasons for Loss of Downforce at Low Ground
  Clearance
• Vortex Breakdown

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Venturi Tunnels

• Venturi effect
• constricts the flow
• creates low pressure
• high velocity flow
• Less pitch sensitive than flat bottom
• Highly regulated to limit cornering speeds

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Underbody Vortices

• Induced vortex speeds up
• flow over F-16 wing
• Vortex Lift
• Vortex Generators speed
• up flow at the front
• Strong stable vortex creates
• suction loads along its trail
• Bernoulli says air
• pressure decreases

Strakes
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Vortex Generators
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• Trips the Boundary Layer, Causing the Laminar Air
  Traveling
• Over the Roof to Become Turbulent
• Typically the size of the boundary layer,
• 15mm - 30mm at the rear end of a vehicle roof

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Effect of VGs on Flow Separation
VG
Separation Region
Separation Region
3
Without VG
With VG
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Effect on Bluff Bodies
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With VG
Without VG

• VGs Cause Drag, but Reduce Pressure Drag by
• Delaying Flow Separation from Occurring
• Reducing the Magnitude of the Separation Region
• Increases the Static Pressure of Separation
  Region

• Higher Velocities Closer to Car,
• Resulting in a Smaller Wake Behind Vehicle

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Wing Endplates

• A Wing with Endplates is Equivalent to
• a Longer Wing Without Endplates
• Effective Aspect Ratio
• Aspect Ratio (AR) Span/Chord
• AR_effective
• AR(11.9(Endplate Depth/Span)

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Gurney Flaps
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Typically 1 to 4 of the Wing Chord Length
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Effect of a Gurney Flap on Flow

• At High Angles of Attack,
• Flow Separates
• Addition of Gurney Flap
• Reattaches Flow
• Can Increase the Downforce
• of the Wing up to 30
• Can Provide the Same
• Amount of Downforce with
• 3O less Angle of Attack

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How a Gurney Flap Works
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• Vortices Reattach Flow and Redirect it Slightly
  Upwards
• Relative to the Flow Over a Clean Wing,
  Implying An
• Increase in Circulation as the cause of
  increased
• Downforce

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Gurney Flap Size Vs. Lift
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Current Research on Gurney Flaps

• Von Karman Vortex Street
• Forms Downstream of
• Gurney Flap
• Fluid of Negative Vorticity
• Becomes Trapped
• Upstream of Gurney Flap
• Trapped Fluid Escapes,
• Interfering Either
• Constructively or
• Destructively with
• Downstream Vortices
• Increases Circulation and
• Downforce

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Additional Aerodynamic Considerations
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Questions ?
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References

• Jang et al, Numerical investigation of an
  airfoil with a Gurney flap 1998
• Katz, Joseph. Aerodynamics of Race Cars 2006
• Koike et al, Research on Aerodynamic Drag
  Reduction by Vortex Generators 2004
• Nikolic, Additional Aerodynamic Features of
  Wing-Gurney Flap Flows 2006
• Sport Compact Car Magazine Automotive
  Aerodynamic Part 2
• Troolin et al, Time Resolved PIV Analysis of
  Flow Over a NACA 0015 Airfoil with Gurney Flap
  2006
• Troolin et al, Time Resolved PIV Analysis of a
  Gurney flap on a NACA 0015 Airfoil 2005
• Troolin et al, The Effect of Gurney Flap Height
  on Vortex Shedding Modes Behind Symmetric
  Airfoils 2006
• Zhang, Xin et al. Ground Effect Aerodynamics of
  Race Cars 2006
• www.army.mil/armyimages/armyimage.php?photo6806
• www.autocult.com.au/img/gallery/997gt3773.jpg
• www.mulsannescorner.com
• www.seriouswheels.com
• www.topgear.com
• www.insideracingtechnology.com/tech107bndrylayer.h
  tm
• http//zedomax.com/blog/2007/04/19/rolling-wind-tu
  nnel-that-goes-at-180mph/