Title: Daimler Aeroacoustic Wind Tunnel: 5 Years of Operational Experience and Recent Improvements
text: Since 2013 the new Daimler Aeroacoustic Wind Tunnel (AAWT) is in operation at the Mercedes-Benz Technology Center in Sindelfingen, Germany. This construction was the second stage of a wind tunnel center project, which was launched in 2007 and started with the climatic wind tunnels including workshop and office areas. The AAWT features a test facility for full-scale cars and vans with a nozzle exit area of 28 m2, a five-belt system, and underfloor balance to measure forces with best possible road simulation. With a remarkable low background noise level of the wind tunnel, vehicle acoustics can be investigated under excellent conditions using high-performance measurement systems. An overview is given about the building and the design features of the wind tunnel layout. The aerodynamic and aeroacoustic properties are summarized. During the first years of operation, further improvements regarding the wind tunnel background noise and vehicle handling were made. Changes in the surface of the contraction and the reduction of rough surfaces in the test section reduced the self-noise of the wind tunnel. For the standard test section configuration (used for daily operation) with smooth center belt, an overall sound pressure level of 57.2 dB(A) could be achieved, for a further optimized configuration with taped gaps and covered shutters and belts even 55.2 dB(A) were measured. Since the manual ride height adjustment of a vehicle in the test section showed to be very time-consuming, a new automatic ride height measuring system was developed. It significantly reduces the setup time before the first measurement. For the rising demands to document surface changes after a test campaign, a separate room for 3D surface scanning was already provided in the workshop area. The technical layout could only be finished with delay. Now the room houses a frontal area measurement system, vehicle lifts, and a robot for 3D surface scanning. This paper describes these new features and reports about the experiences of the first years of operation.