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EXPERIMENTAL COEFFICIENT OF
DRAG DETERMINATION FOR A
SOLAR-POWERED VEHICLE
Lab Group 4
ASE 120K Fall 2009
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Introduction
University of Texas entry in North
American Solar Challenge
Determine the coefficient of drag Test at various Reynolds numbers
ranging from 6x104 and 4.9x105
Will compare results to MIT car from
December 2005 (5)
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Background
1/16th scale
Dynamic similarity off by a factor of 16
MIT Tests (5)
y How were they done?
y What was gained?
y How this affects our study?
Additional studies drawn from AIAAJournal and Journal of WindEngineering
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Background (contd)
Car testing in wind tunnels
y Have to be aware of boundary layer growth
on driving surface
Placing model on raised surface starting very
close to front of model
Other solutions unfeasible
y Formation of wake
Have pitot static tube set up 1 ft behind car
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Apparatus
Closed-circuit subsonic wind tunnel
Model
y
1/16th
scaley 3D printer
y Plate-mounted
Pitot-static tube array
Flow visualization
y Smoke wire (ideally)
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Procedure
Build Modely 3D Printer
y Coat model
Test flat plate alone Mount model on flat plate in wind tunnel
Visualize flow at 10 ft/s increments
Obtain pitot-static tube array datay
2,000 samples per site at 500 Hzy Test Area 4.75 in x 3.5 in
y Test at 1/8 in (~3mm) intervals between sites Forms grid of 1008 points per wind tunnel setting
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Data Evaluation
Use Pitot Static data to create wake
profile at each Reynolds number
y Momentum deficit method
Use flat plate wake height to determine
boundary layer interference on bottom of
the car
Generate a total drag coefficient at eachReynolds number
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Table of contents
Background
Comparison to other works
Apparatus Procedures
Testing
Results Conclusions
Further Research
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Background
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Other relevant tests
Wind tunnel testing of full size vehicles
(Ford, GM, and European wind tunnels)
MIT tests
y How they were done?
y What they found
Reynolds #s
CD calculated
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Apparatus
y Model car
y Flat plate
y Wind tunnel
y Tuftsy Smoke wire
y Pitot rake
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Procedure
Plate testsy Done to insure no turbulent interference from
plate in the test area
Car testsy Finding true test area
y Use of pitot rake
y 10 pitot tubes pressures taken at 53 differentpoints then moved up and done again making20*53 or 1060 points
Flow visualizationy Why done after
y Smoke wire and tufts tests
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Findings
Picture of flow
visualization
y Can either do one
slide for each, smokeand tufts,
y Or do one slide of
both, smoke and tufts
y Bluff bodies of the
wheel wells and thecanopy causes
separation bubbles
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Findings continued
Show final surface graph(s)
y Could show just one and explain how this is
the basic shape
y Or could show all and point out differences
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Results
Reynolds #s Coefficient of Drag
1.587e5 0.00611
2.0489e5 .00396
2.4889e5 .0125
2.9801e5 .0183
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Conclusions
Redesign the solar car if decrease in
drag is desired
Find a way to divert flow from around
the canopy, or keep the flow attached
longer
Drive slower
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Advice for later experiments
Larger model can be used, more
accurate
Keep a close eye on the plate boundary
layer
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Questions?
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References
(1) A. Albers, J. Brys, S. Illg, J. Roop, and J. Ashworth. June 2003. EXPERIMENTALWAKEINVESTIGATION OF IDENTICALCARS IN CLOSE PROXIMITY.American Institute of Aeronauticsand Astronautics.
.
(2) P.W. Bearman. July 1997. Near wake flows behind two- and three dimensional bluff bodies.Journal of Wind Engineering and Industrial Aerodynamics.
.
(3) R. Born. Wind Tunnel Experiment: Mercedes-Benz CLK vs. Duesenberg.All Car Models..
(4) Y. Sakuma and A. Ido. Wind Tunnel Experiments on Reducing Separated Flow Region AroundFront Ends of Vehicles on Meter-Gauge Railway Lines. Japan Science and Technology InformationAggregator.
.
(5) P. Augenbergs. Aerodynamic Optimization of a Solar Powered Race Vehicle. Massachusetts
Institute of Technology. .
(6) Anderson, J.D. (2005) Fundamentals of Aerodynamics. Fourth Edition McGraw Hill, Inc.
(7) Tinney, C.E. (2009) ASE120k Laboratory Handbook. Dept of Aerospace Engineering andEngineering Mechanics at The University of Texas at Austin.
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