NASCAR Aerodynamics

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NASCAR Aerodynamics

• BY Mark Angeloni
• Brendon Keinath
• Todd Sifleet

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Why Does it Matter?

• At high speed aerodynamic effects play an
  enormous role in car performance.
• By taking advantage of the effects of lift
  racecars have been able increase their corning
  ability, which in turn decreases lap time.
• Also by minimizing drag they can maximize the top
  speed of the car.

Source Race Car Aerodynamics, J. Katz, 1995
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Model Testing in a Wind Tunnel

• We used a 1/12 scale model of a NASCAR, because
  full-scale prototype testing is more expensive
  and time consuming
• By running the model in wind tunnel at different
  velocities we are able to model different actual
  car velocities, gathering relevant information
  concerning aerodynamics.

Source Union College
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Model Testing

• Problems With Model Testing
• Not possible to match Reynolds Number
• Wind Tunnel cannot reach necessary speeds
• If it could, Mach number would be too large and
  wed have to worry about compressibility
• Some ways to fix this problem are
• A larger wind tunnel with larger models
• A different testing fluid with a higher density
• Pressurizing and/or adjusting the air temp in the
  wind tunnel
• Or in our case running the wind tunnel at several
  velocities and extrapolating to determine useful
  information.

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The Experiments

• Week 1- Surface Pressure measurements
• Week 2- Lift and Drag measurements
• Week 3- Particle Image Velocimetry, CFD analysis

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Surface Pressure Measurments

• We used a model outfitted with 17 pressure taps
  to take pressure measurements at different point.
  
• We measured the pressure at 2 different
  velocities 31 mph, and 51.5 mph.
• Using these pressures we calculated pressure
  coefficients at different points of the model.
• Using Cp we can calculate pressures at any given
  point on the actual NASCAR.

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Results - Pressure
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Coefficient of Pressure
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Lift and Drag

• The model, was connected to a dynamometer that
  measured force in both the x and y direction,
  essentially lift and drag. 
• This data was collected using a data acquisition
  system as well, and processed with a PC.  
• Using these measurements it was possible to
  calculate lift and drag on the car, as well as
  lift and drag coefficients.

Source Brad Bruno
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Results Lift
Shows the Coefficient of Lift compared to the
Reynolds Number of the experiment
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Results - Drag
Displays the coefficient of drag on the car
compared to the Reynolds Number of the
Experiment.
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Particle Image Velocimetry

• PIV uses the wind tunnel along with a double
  pulsed laser technique to measure instantaneous
  velocity and to map out the flow field.
• This provides a visual representation of the flow
  along the vehicle, streamlines and a qualitative
  representation of the velocities.

Source Brad Bruno
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Results - PIV
Flood Contour of Ford NASCAR
Streamline Contour of Ford NASCAR
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Results - PIV
Zoomed In view of back end of NASCAR
Zoomed in view of front end of NASCAR
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Computational Fluid Dynamics

• CFD is a mathematical approach to modeling the
  flow around a vehicle. It uses an advanced
  computer program to map the flow field.
• Like PIV, CFD gives qualitative representation of
  the velocity and pressure around the vehicle.

Source Google Images
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Results CFD, Velocity
CFD of velocity of flow over car
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Results CFD, Pressure
CFD of velocity of flow over car
CFD of pressure distribution as a result of flow
over car
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Results CFD, Cp
CFD of pressure coefficient as a result of flow
over the car
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Racecar Progression

• Reduction in aerodynamic drag by streamlining the
  shape of the vehicle
• Increase the down force, negative lift, to
  increase cornering speeds
• Raw hp vs. streamlining

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The Proof is in the PIV

• The General Lee has a box like shape which
  results in a larger Drag than a rounder shape
• Cd
• Cube 2.2
• Rounded Cube 1.2
• Sphere 0.3
• Triangle 1.5

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Charger vs NASCAR
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Drag on Charger vs. NASCAR
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Spoiler Effect

• The addition of a spoiler on the car results in
  greater downward force (or negative lift) which
  results in better cornering
• The addition of a spoiler also increases the
  amount of drag on the car

Source Images.google.com
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With or Without Spoiler
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Why Drivers Draft

• Behind the car is a low pressure/low velocity
  pocket which aids in the reduction of drag on the
  following car
• This increases efficiency and speed for both cars

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Drafting
Courtesy of trickelfan.com
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What we learned

• The strides made in streamlining designs of cars
  aided in decreasing the drag force along a
  vehicle
• Spoilers create a larger down force on the
  vehicle which helps in keeping the wheels in
  solid contact with the ground at high speeds and
  cornering
• These concepts together help increase speeds and
  lap times which is the overall goal

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Is the data gathered useful?

• At High Reynolds Numbers the Coefficient of Drag
  and the Coefficient of Lift level off
• We are in the transition area
• The trends of our data do not quite level off so
  we can approximate the actual coefficients but
  cant exactly place them