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By Mauricio Blanco, Technical Officer, National Research Council–Institute for Fuel Cell Innovation, Vancouver, Canada
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The 2004 UBCST entry on the Start Line, ready to go
The Supermileage® competition provides engineering and technology
students with a challenging design project that involves the
development and construction of a single-person, fuel-efficient
vehicle. Vehicles are powered by a small four-cycle engine. Students
have the opportunity to set a world fuel economy record and increase
public awareness of fuel economy. The engines are donated by Briggs
& Stratton.
In 2003 and 2004, the University of British Columbia Supermileage
Team (UBCST) won the Supermileage competition with mileages of
927 and 1747 miles per gallon (US), respectively. Their current goal is
to continue to improve their designs and manufacturing methods
through innovative and effective ideas.
Besides the engine, an efficient drive train, a well-designed yet light
frame, and an aerodynamic car body are vital components for low
mileage consumption. Because the cars at the Supermileage competition
run at low speeds (with a minimum average of 15 mph), the
aerodynamic shapes are extremely important. For this reason, the
UBCST spent a great deal of time on the design and development of
the 2004 body using wind tunnel testing (with 1/4 and 1/2 scale
models) and CFD analysis using FLUENT.
Total pressure on the surface of the 2003 model
 
Surface pressure distribution (top) and streamlines (bottom) for the revised body,
which was not used in the competition
First, the aerodynamic behavior of the 2003 body was tested and
improved from both an aerodynamic and manufacturing standpoint.
A CFD analysis was performed, and followed by a wind tunnel test of
the male mold used to manufacture the body, and a 1/4 scale model.
The numerical simulation used the Spalart-Allmaras turbulence model
with an inlet velocity of 60 km/s, which resulted in a drag coefficient
of 0.16. Although this coefficient is acceptable, the body had two
additional problems. It was difficult to manufacture (as experienced
by the team a year earlier), and the driver’s space was very limited.
Thus, three different concept models were designed following the
geometrical characteristics of the existing frame and engine housing.
Once the models were created using 3D modeling software, each was
analyzed using FLUENT for two different conditions: laminar and turbulent
flow. The turbulent conditions gave the closest results to the
ones observed in the wind tunnel tests. After the numerical simulations
were completed, a 1/2 scale model of the best new design was
built and tested in the wind tunnel. While the numerically predicted
drag coefficient of 0.11 was confirmed by the wind tunnel results, the
lateral area of the model was greater than that for the 2003 version,
so its performance in cross-winds would not be as good. As a result of
these analyses and tests, the team decided to re-use the 2003 body
with certain modifications (better windows and surface finish) while
further designs were considered.
Currently, the UBCST Aero team is finishing the design of the new
2005 body, which, based on preliminary CFD analysis and wind tunnel
testing, has a drag coefficient of 0.12 and should have a better
aerodynamic shape for cross winds.
More information
www.mech.ubc.ca/~supermileage/2003/main.html
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