Real road test
Volvo invests in a wind-generating chamber that simulates on-road airflow
around and under a car’s body. Siobhan Wagner reports
A WIND tunnel that simulates airflow
around and under a car’s body is helping
the design of vehicles that use less fuel
and emit less carbon dioxide.
The new 27m 2 wind-generating
chamber was recently installed at
Volvo’s facility in Gothenburg, Sweden.
It has four steel belts to rotate car
wheels at motorway pace and a giant
5MW fan to generate the corresponding
air speed a vehicle would be driving
against.
These features, the company believes,
will help engineers better understand
aerodynamic forces in real-life driving
conditions.
Volvo invested €20m (£16m) in the
tunnel to direct more focus on the
aerodynamics of a vehicle’s underside
and wheels, which account for
more than 50 per cent of a car’s total
air drag.
This sort of information cannot be
studied in traditional wind tunnels where
vehicles stand still in a flow of air.
Tim Walker, an aerodynamics
expert at Volvo, explained that the old
methods are a little like measuring the
aerodynamic properties of a car that is
standing still in a car park during a
powerful storm.
He said the tunnel has been designed
to exactly replicate airflow around and
underneath the car when driving on a
real road with dragging wind speeds of up
to 96mph. The tunnel creates these with
8m carbon fibre blades.
It is also equipped with four flat steel
belts to spin all the wheels. One central
belt, 5.3m long and 1m wide, simulates
the road under the moving car. The
moving ground can reach speeds of up to
161mph.
The test car is connected to a highly
sensitive balance using four small
struts. These hold the car in position
while its weight is transferred from
the tyres to the balance through the flat
steel belts.
Walker explained that this makes it
possible to load up the wheels and tyres
exactly as they are when driving on the
road. The balance, he said, is so sensitive
Unlike traditional
wind tunnels, the
chamber is
designed to focus
more on the
aerodynamics of a
vehicle’s
underside and
wheels
that it would react even if ‘the world’s
smallest mobile phone’ was tossed on to
the front seat.
Volvo is already seeing promising
results from the chamber. Walker said
the company’s team of engineers has
succeeded in reducing air resistance in
the new Volvo C30 DRIVe by more than
10 per cent compared with the current
C30 1.6D. This in turn, he explained,
leads to about three grams lower CO 2
emissions/km.
The tests also show that this reduces
fuel consumption by just over
0.1l/100km. However, Volvo estimated
that in a real driving situation, with
higher speed and air resistance, the
actual saving in fuel could be twice
the EnGIneeR 13–26 OCTOBER 2008 41
that. According to the company’s
figures, a driver who covers 15,000km a
year will save about 45l of fuel —
almost a full tank in a Volvo C30.
These savings and emission
reductions are due to refinements made
to the C30 DRIVe’s roof spoiler, rear
bumper and under-floor panels. But
the improvements would not have been
made based on measurements from
the original wind tunnel, said
Walker, where the focus was on the
body of the car.
In the new chamber, he said, he and
his colleagues are able to obtain an
overall picture that takes the
car’s underside and the wheels
into account.
AERODYNAMICS
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