The water is cooled in large vats at the far end of the tunnel. The air produced by the turbine flows in a circle, being moved around either end of the structure by deflector flaps. The car rests on a treadmill, which when activated moves at 90 mph. Single pieces or multiple parts can be tested as data flows into a computer in the control room. The control room, which is soundproof, has a large window facing the vehicle model being tested.
Technicians sit at various computers.
One large computer accepts rows of numbers under various categories from car-attached sensors and displays them every few seconds to fill a lengthy chart. After a test is complete, the crew makes adjustments or adds different parts to learn what is compatible. There are a couple safety nets in case a part should come loose. We measure the wheel drag separately. Watching from the control room, it appears the treadmill is not moving during the operation.