Volvo's new wind tunnel test

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 27m² 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 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 CO₂ 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 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.