Aeroacoustic wind tunnel
Aeroacoustic wind tunnels are wind tunnels for aeroacoustic investigations mainly in the field of vehicle and aerospace engineering. In these special wind tunnels, the very loud electrical noises of the drive and the aerodynamic noises on the fan and in the air duct of the wind tunnel are subsequently reduced so that they do not interfere with the noises of the (aircraft) vehicle that are actually being examined.
construction
First of all, the blower noise must be kept away from the measuring section . In addition, built-in parts (e.g. safety nets) are to be arranged in such a way that the noises generated by them cannot be heard in the measuring section as far as possible. Further measures concern the measuring section itself: it is generally designed to be low-reflection , with the walls of the measuring hall being clad with absorbers . This is much easier to implement for open than for closed or slotted measuring sections.
In the first aeroacoustic wind tunnels, noise reduction was achieved using sound absorbers and coatings made from fiber materials . The fiber materials flowed around had the disadvantage that particles could be carried away by the air, which affected both the acoustic effectiveness and the air quality.
In newer wind tunnels, therefore, alternative fiber-free sound absorbers are mostly used, which consist of a combination of foams and plate or membrane absorbers . The foams are tuned to the higher frequency range , while the absorbers absorb the lower-frequency noise components.
Membrane absorbers consist of flat backdrops that are usually approx. 10 cm thick and consist of a combination of plate transducers with Helmholtz resonators . This is achieved by an arrangement of hollow chambers that have a volume of approx. 0.5 to 5 liters. They are covered with a perforated or slotted metal membrane . A second oscillating metal membrane is applied over all the chambers of a backdrop. The membrane absorber backdrop is thus a closed body made of just one material (mostly stainless steel or aluminum ). The adjustment of the absorber to the desired frequency range takes place via the parameters chamber volume, thickness of the metal membrane, slot width and distance between cover and slot membrane.
Locations
In Germany there are special aeroacoustic wind tunnels and the like. a. in
- Weissach ( Porsche ),
- Sindelfingen ( Mercedes ),
- Munich ( BMW ),
- Ingolstadt ( Audi ),
- Braunschweig ( German Aerospace Center ) and
- Stuttgart ( Research Institute for Automotive Engineering and Vehicle Engines , the only vehicle wind tunnel that is independent of industry).
Renowned foreign wind tunnels are u. a. in
- Emmeloord (NL) ( German-Dutch wind tunnel , DNW) and
- Montigny le Bretonneux near Versailles (F) ( PSA - Renault - S2A wind tunnel ).
literature
- ME Goldstein: Aeroacoustics . McGraw-Hill Books, New York 1976, ISBN 0-07-023685-2 .
- T. Schütz (Hrsg.): Hucho - aerodynamics of the automobile . Springer Vieweg, Wiesbaden 2013, ISBN 978-3-8348-2316-8 .
- M. Helfer, J. Wiedemann : Design of Wind Tunnels for Aeroacoustics . Lecture Series Experimental Aeroacoustics ; November 13 to November 17, 2006. From Karman Institute , Rhode-St.-Genèse, Belgium 2006, ISBN 2-930389-70-2 .
Web links
- Aeroacoustic wind tunnel at the Research Institute for Automotive Engineering and Vehicle Engines Stuttgart - FKFS