Wind Tunnel Aerodynamics 2016

Erika Clifford, Evan Lerner, Garrett Cook, Katie Megerian, Max Kang, Rebecca Martin, and William Aherne

Overview● Introduction● Models● Preparation● Experiment 1:

Pressure Measurements ● Modifications● Experiment 2: Wake Measurements● Experiment 3: Flow Visualization● Conclusion

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IntroductionPurpose

To carry out experiments on scaled down automobile models in order to determine and analyze aerodynamic characteristics

Tasks

● Model Preparation● Wind Tunnel Set-up● Different Measuring Techniques

○ Pressure○ Force○ Flow Visualization

● Improvement of Aerodynamic Behavior3

Recurring Terms● Static Pressure: experienced by a fluid particle as it moves near a surface.

● Stagnation Pressure: experienced when a flowing fluid decelerates to zero velocity without friction.

● Dynamic Pressure: difference in the stagnation and static pressure.

● Freestream: uninterrupted air flow towards the model

● Drag Coefficient: dimensionless value demonstrating strength of drag force

● Wake: area of turbulent flow behind the car

● Boundary Layer: attaches air-flow to car. When this separates off the car, drag is created

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Models 1:18 Scale (Pictures)

Porsche Panamera Turbo Ford Mustang Lamborghini Gallardo

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Model Preparation ● Determine x- and y-positions of pressure taps● Drill pressure taps on top and bottom of model● Connect metal tubes using superglue and epoxy● Smooth hole surface using filler● Connect small plastic tubes to metal pipes for pressure measurement

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Air flow

Y

X

P∞

Prandtl tube

Capacitance Manometer

Difference in static pressures

Experiment 1: Pressure Measuring

Resistance Thermometer(pt-100)

Temperature measurement

P∞Pi

* Please refer to each car’s poster for individual graphs and data

Modifications to Reduce Drag Porsche:● Tape windows closed● Cover windshield and

hood grooves with clay

Mustang:● Taped windows closed● Hood edges rounded● Grooves filled in● Back end rounded

Gallardo:● Rear extension● Addition of clay● Wheels and windows

covered

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Experiment 2: Wake Measuring

* Please refer to each car’s poster for individual graphs and data9

Air flow

YX

Capacitance Manometer

PtP∞

Prandtl tube

Capacitance Manometer

P(y)

0 (cm) 48 70 81.5

Difference in static pressures

Dynamic pressure in wake

Comparing Velocity Profiles

10Velocities Scaled

Experiment 3: Flow VisualizationThree videos were taken of smoke streaklines along the axis of models at airspeeds of 1 m/s, 1.4 m/s and 2.5 m/s for both the modified and unmodified cars. ● Modifications delayed boundary layer separation● Wake size was reduced and as a result so was drag

Original Model Modified Model 11

Reduction in size of wake

Unmodified Modified12

Conclusions● Experiment 1 provided an accurate estimation for points of flow separation

● Experiment 2 verified that changing geometry affects drag

● Experiment 3 created a visual representation of the difference in flow

separation between the modified model and the original model

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Questions?

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