U-BEND SILENCERS FOR AN AEROACOUSTIC WIND -TUNNEL

The paper describes construction measures for the acoustic improvement of an aero-acoustic wind tunnel which mainly serves for the testing o f road vehicles. The solution introduced consists of membrane absorber baffles installed in the ducts on both sides of the fan thus providin g sufficient damping at low frequencies and of bending vanes profiled with porous Polyester foam covered by a thin coating which are placed in each of the four corners in order to attenuate medium and high freq uencies of the noise emitted into the measuring hall. Moreover, for ab sorption purposes, the measuring hall was lined with a novel type of b roadband absorbers consisting of Polyester foam plates mounted in fron t of membrane absorbers. The solution applied in the flow duct takes a dvantage of the specific virtues of membrane absorbers, i.e. their sle nder construction with a total thickness of only 212 mm as well as the ir smooth surfaces. In the wind tunnel both these advantages yield an only slight loss in the maximum flow velocity achievable. The paper de als with the aeroacoustic improvement of a wind tunnel which is not on ly of use in the automotive industry but just as well in aircraft rese arch. The aeroacoustic performance of wind tunnels plays an important role e.g. when the how noise of aircrafts is being tested. The methods and materials presented herein may therefore recommend themselves as retrofit measures applicable to many existing wind tunnels.