NASCARNASCAR AerodynamicsAerodynamics

BY: Mark AngeloniBY: Mark Angeloni

Brendon KeinathBrendon Keinath

Todd SifleetTodd Sifleet

Why Does it Matter?Why Does it Matter?

At high speed At high speed aerodynamic effects play aerodynamic effects play an enormous role in car an enormous role in car performance.performance.

By taking advantage of By taking advantage of the effects of lift the effects of lift racecars have been able racecars have been able increase their corning increase their corning ability, which in turn ability, which in turn decreases lap time. decreases lap time.

Also by minimizing drag Also by minimizing drag they can maximize the they can maximize the top speed of the car. top speed of the car.

Source: Race Car Aerodynamics, J. Katz, 1995

Model Testing in a Wind Model Testing in a Wind TunnelTunnel

We used a 1/12 scale We used a 1/12 scale model of a NASCAR, model of a NASCAR, because full-scale because full-scale prototype testing is prototype testing is more expensive and more expensive and time consuming time consuming

By running the model By running the model in wind tunnel at in wind tunnel at different velocities we different velocities we are able to model are able to model different actual car different actual car velocities, gathering velocities, gathering relevant information relevant information concerning concerning aerodynamics. aerodynamics. Source: Union College

Model TestingModel Testing

Problems With Model TestingProblems With Model Testing Not possible to match Reynolds NumberNot possible to match Reynolds Number Wind Tunnel cannot reach necessary speedsWind Tunnel cannot reach necessary speeds If it could, Mach number would be too large and we’d If it could, Mach number would be too large and we’d

have to worry about compressibilityhave to worry about compressibility Some ways to fix this problem are:Some ways to fix this problem are:

A larger wind tunnel with larger modelsA larger wind tunnel with larger models A different testing fluid with a higher densityA different testing fluid with a higher density Pressurizing and/or adjusting the air temp in the wind Pressurizing and/or adjusting the air temp in the wind

tunneltunnel Or in our case running the wind tunnel at several Or in our case running the wind tunnel at several

velocities and extrapolating to determine useful velocities and extrapolating to determine useful information.information.

The ExperimentsThe Experiments

Week 1- Surface Pressure Week 1- Surface Pressure measurementsmeasurements

Week 2- Lift and Drag measurementsWeek 2- Lift and Drag measurements

Week 3- Particle Image Velocimetry, Week 3- Particle Image Velocimetry, CFD analysisCFD analysis

Surface Pressure Surface Pressure MeasurmentsMeasurments

We used a model outfitted We used a model outfitted with 17 pressure taps to with 17 pressure taps to take pressure take pressure measurements at different measurements at different point. point.

We measured the pressure We measured the pressure at 2 different velocities 31 at 2 different velocities 31 mph, and 51.5 mph.mph, and 51.5 mph.

Using these pressures we Using these pressures we calculated pressure calculated pressure coefficients at different coefficients at different points of the model. points of the model.

Using CUsing Cpp we can calculate we can calculate pressures at any given pressures at any given point on the actual point on the actual NASCAR.NASCAR.

)21(

)(

2V

ppC p

Results - PressureResults - Pressure

Coefficient of PressureCoefficient of Pressure

Lift and DragLift and Drag

The model, was connected The model, was connected to a dynamometer that to a dynamometer that measured force in both the measured force in both the x and y direction, x and y direction, essentially lift and drag.  essentially lift and drag. 

This data was collected This data was collected using a data acquisition using a data acquisition system as well, and system as well, and processed with a PC.   processed with a PC.  

Using these measurements Using these measurements it was possible to calculate it was possible to calculate lift and drag on the car, as lift and drag on the car, as well as lift and drag well as lift and drag coefficients. coefficients.

Source: Brad Bruno

)21(

)21(

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AV

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Results – LiftResults – Lift

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

Coefficient of Lift vs. Reynolds Number

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Reynolds Number

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Results - DragResults - Drag

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

Coefficient of Drag vs Reynolds Number

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Reynolds Number (width)

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Particle Image VelocimetryParticle Image Velocimetry

PIV uses the wind tunnel PIV uses the wind tunnel along with a double along with a double pulsed laser technique to pulsed laser technique to measure instantaneous measure instantaneous velocity and to map out velocity and to map out the flow field.the flow field.

This provides a visual This provides a visual representation of the flow representation of the flow along the vehicle, along the vehicle, streamlines and a streamlines and a qualitative representation qualitative representation of the velocities. of the velocities.

Source: Brad Bruno

Results - PIVResults - PIV

Flood Contour of Ford NASCAR

Streamline Contour of Ford NASCAR

Results - PIVResults - PIV

Zoomed In view of back end of NASCAR

Zoomed in view of front end of NASCAR

Computational Fluid Computational Fluid DynamicsDynamics

CFD is a mathematical CFD is a mathematical approach to modeling approach to modeling the flow around a the flow around a vehicle. It uses an vehicle. It uses an advanced computer advanced computer program to map the flow program to map the flow field. field.

Like PIV, CFD gives Like PIV, CFD gives qualitative qualitative representation of the representation of the velocity and pressure velocity and pressure around the vehicle. around the vehicle.

Source: Google Images

Results – CFD, VelocityResults – CFD, Velocity

CFD of velocity of flow over car

Results – CFD, PressureResults – CFD, Pressure

CFD of velocity of flow over car

CFD of pressure distribution as a result of flow over car

Results – CFD, CResults – CFD, Cpp

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

Racecar ProgressionRacecar Progression

Reduction in Reduction in aerodynamic drag by aerodynamic drag by streamlining the shape streamlining the shape of the vehicleof the vehicle

Increase the down force, Increase the down force, negative lift, to increase negative lift, to increase cornering speedscornering speeds

Raw hp vs. streamliningRaw hp vs. streamlining

The Proof is in the PIVThe Proof is in the PIV The General The General

Lee has a box Lee has a box like shape like shape which results which results in a larger in a larger Drag than a Drag than a rounder shaperounder shape

Cd:Cd:Cube = 2.2Cube = 2.2Rounded Cube Rounded Cube

= 1.2= 1.2Sphere = 0.3Sphere = 0.3Triangle = 1.5Triangle = 1.5

Charger vs NASCARCharger vs NASCAR

Drag on Charger vs. NASCARDrag on Charger vs. NASCARCoefficient of Drag vs. Re

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NASCAR w/o spoilerCharger

Spoiler EffectSpoiler Effect

The addition of a The addition of a spoiler on the car spoiler on the car results in greater results in greater downward force (or downward force (or negative lift) which negative lift) which results in better results in better corneringcornering

The addition of a The addition of a spoiler also increases spoiler also increases the amount of drag the amount of drag on the caron the car

Source: Images.google.com

With or Without SpoilerWith or Without SpoilerCoefficient of Downforce

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NASCAR w/o spoilerNASCAR w/ Spoiler

Why Drivers DraftWhy Drivers Draft

Behind the car is a Behind the car is a low pressure/low low pressure/low velocity pocket velocity pocket which aids in the which aids in the reduction of drag reduction of drag on the following on the following carcar

This increases This increases efficiency and efficiency and speed for both carsspeed for both cars

DraftingDrafting

Courtesy of trickelfan.com

What we learnedWhat we learned

The strides made in streamlining designs The strides made in streamlining designs of cars aided in decreasing the drag force of cars aided in decreasing the drag force along a vehiclealong a vehicle

Spoilers create a larger down force on the Spoilers create a larger down force on the vehicle which helps in keeping the wheels vehicle which helps in keeping the wheels in solid contact with the ground at high in solid contact with the ground at high speeds and corneringspeeds and cornering

These concepts together help increase These concepts together help increase speeds and lap times which is the overall speeds and lap times which is the overall goalgoal

Is the data gathered useful?Is the data gathered useful?

At High Reynolds Numbers the At High Reynolds Numbers the Coefficient of Drag and the Coefficient of Drag and the Coefficient of Lift level offCoefficient of Lift level off

We are in the transition areaWe are in the transition areaThe trends of our data do not quite The trends of our data do not quite

level off so we can approximate the level off so we can approximate the actual coefficients but can’t exactly actual coefficients but can’t exactly place themplace them