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Vehicle Design
Drag Force
Optimizing
aerodynamic drag not only reduces fuel consumption, but it can also
increase vehicle performance at high speeds and lower aerodynamic
noise. At high speeds, most fuel is utilized to overcome the
aerodynamic drag force, the resistance created by the air flow.
Aerodynamic resistance is created from pressure resistance due to
vehicle shape, air friction resistance over the vehicle surface, and
density resistance from extruding parts (ie. mirrors) and internal
vehicle ducts. The greatest effect (70%) is caused by pressure
resistance which depends on many vehicle design factors such as the
front spoiler, the shape of the vehicle front, the angle of
inclination of the rear window and the shape of the vehicle rear.
Wind
Tunnel Testing with Lamborghini to determine Aerodynamic Performance
The Drag force
value for a moving vehicle is given by the following expression:
·
D = ½ *CD*A*ρ*V2
Where
o
CD
is the drag coefficient
o
A
is the projected frontal area of the vehicle
o
ρ
is the density of air
o
V
is the speed of the vehicle relatively to the air
Lowering the
drag through vehicle design will reduce vehicle drag and optimize
fuel economy. Since frontal area is usually pre-determined for a
certain vehicle program, lowering the drag coefficient through an
aerodynamic design offers the
best opportunity to reduce vehicle drag and therefore optimize fuel
economy.
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EAST
Lab - University of Michigan
