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NASCAR Aerodynamics

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					NASCAR Aerodynamics

BY: Mark Angeloni Brendon Keinath Todd Sifleet

Why Does it Matter?
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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

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.
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Source: Union College

Model Testing
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Problems With Model Testing
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Some ways to fix this problem are:
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Not possible to match Reynolds Number  Wind Tunnel cannot reach necessary speeds  If it could, Mach number would be too large and we’d have to worry about compressibility 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.

The Experiments
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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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( p  p ) Cp  1 (   V 2 ) 2

Results - Pressure

Coefficient of Pressure

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.
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Source: Brad Bruno

CL 

FL

1 2 (    V  A) 2 FD CD  1 (    V 2  A) 2

Results – Lift
Coefficient of Lift vs. Reynolds Number
0.08 0.06

Coefficient of Lift

0.04 0.02 0.00
100000 120000 140000 160000 180000 200000 220000 240000 260000

-0.02 -0.04 -0.06

Reynolds Number
Shows the Coefficient of Lift compared to the Reynolds Number of the experiment

Results - Drag
Coefficient of Drag vs Reynolds Number
1.4 1.2

Coefficient of Drag

1.0 0.8 0.6 0.4 0.2 0.0

100000 120000 140000 160000 180000 200000 220000 240000 260000

Reynolds Number (width)

Displays the coefficient of drag on the car compared to the Reynolds Number of the Experiment.

Particle Image Velocimetry
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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

Results - PIV

Flood Contour of Ford NASCAR

Streamline Contour of Ford NASCAR

Results - PIV

Zoomed In view of back end of NASCAR

Zoomed in view of front end of NASCAR

Computational Fluid Dynamics
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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

Results – CFD, Velocity

CFD of velocity of flow over car

Results – CFD, Pressure

CFD of velocity of flow over car

CFD of pressure distribution as a result of flow over car

Results – CFD, Cp

CFD of pressure coefficient as a result of flow over the car

Racecar Progression
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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

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

Drag on Charger vs. NASCAR
Coefficient of Drag vs. Re
1.6 1.4

NASCAR w/o spoiler Charger

Coffiecient of Drag

1.2 1 0.8 0.6 0.4 0.2 0 80000

100000 120000 140000 160000 180000 200000 220000 240000 260000 280000

Re

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
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Source: Images.google.com

With or Without Spoiler
Coefficient of Downforce
0.12 0.1 0.08 0.06 NASCAR w/o spoiler NASCAR w/ Spoiler

CL

0.04 0.02 0 80000 -0.02 -0.04

100000 120000 140000 160000 180000 200000 220000 240000 260000 280000

Re

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

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 can’t exactly place them
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