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Aerodynamic resistance and noise development have a considerable effect on a vehicle’s comfort and economy. Audi’s aeroacoustic wind tunnel is one of the most modern in the world and offers a practically unlimited range of tests.
A top speed of 300 km/h: even the Audi R8’s top speed can be simulated here. With its low noise rotor measuring some five metres in diameter, the fan in the aeroacoustic wind tunnel has an output of 2.6 megawatts. The accelerated air travels along a tubular section with four corners which prevent turbulence and background noise. Before entering the test section, the air flow passes through three screens and a nozzle. Now, largely free of turbulence, constant and directionally uniform, the air flow accelerates up to 300 km/h. It now enters the test section.
The test section: flexible and realistic
The 9.5 metre long test section fulfils every requirement for aerodynamics and acoustics. Its central element is the scale. This measures the forces acting on the vehicle. The aerodynamics are improved, resulting in better economy, performance and safety. Acoustic measurements in the wind tunnel are used to optimise comfort while travelling. The measurement technology involved in this makes use of so-called dummy heads to gain a realistic impression of the sounds. Certain sounds can only be located and analysed at high wind speeds.
Realistic statements about the flow relationships
Unlike conventional wind tunnels, Audi’s aeroacoustic wind tunnel even has a floor that moves. As the track-wide belt moves, it simulates the movement of the road in relation to the vehicle. In addition, four small moving belts under the wheels provide an authentic representation of the rotation of the wheels. Undistorted measurements: the supports to hold the vehicle are located in the slipstream of the front wheels. The barrier layer caused by the friction of the air against the ground is drawn off immediately in front of the moving belt.
Active und passive noise suppression
The collector is positioned behind the test section: the funnel-shaped opening guides the air back in the direction of the fan. Before it gets there, it passes the anti-noise equipment patented by Audi. This consists of loudspeakers that neutralise the air flow noises by emitting counter-frequencies to eliminate them. Absorbent materials that line the aeroacoustic wind tunnel provide passive noise damping.