The Silent Low-speed wind tunnel (LNB) is an atmospheric wind tunnel of Eiffel-design with a modular testsection. The test section with its cross-section of 0,4 m x 0,6 m provides great optical access, the maximum velocity is 19 m/s. The surrounding of the tunnel is equipped with sound insulation, minimizing acoustic disturbance. Various PIV-systems, static and time-resolved are used, as well as a force balance and PSI pressure scanners.
The LNB is a continuous atmospheric Eiffel-type wind tunnel with a closed test section. The settling chamber with nozzle, the diffuser and the motor mounting are made from glass fibre reinforced epoxy and the test section is transparent for using optical measurement techniques. A 3 kW motor drives the tunnel in suction mode, which gives a maximum flow velocity of 19 m/s. The wind tunnel is installed in a 8,2 m long room, which allows circulation of the flow. The ceiling of the room is covered with open-celled acoustic foam to damp noise. To minimize vibrations, the wind tunnel is mounted on rubber absorbers that are fastened on a steel construction. Motor and fan are decoupled from the rest of the tunnel.
Continuous atmospheric Eiffel wind tunnel
Glass fibre reinforced epoxy construction
Closed test section ( 600 mm x 400 mm x 1500 mm )
Motor el. power P = 3 kW
Max. Velocity U = 19 m/s
Tu < 0,1% at 10 m/s
Velocity uniformity 1%
The wind tunnel nozzle has a rectangular cross section with a Burger-type axial area distribution. The contraction ratio is about 16 to achieve low-turbulence flow in the test section. The nozzle walls are reinforced with sandwich plates in order to suppress low-frequency vibrations. The exterior wall is covered with acoustic foam plates to suppress noises reflections. At the inlet of the nozzle, different devices are installed to reduce turbulence and to achieve a uniform flow. At first the air flows through a 30 mm thick fleece mat. It then passes through a honeycomb made of aluminium which straightens the flow. The honeycomb has a length of 133 mm in flow direction and an averaged diameter of 14 mm. Then the air passes through a fine woven screen to decrease the size of the turbulent structures. The following high contraction accelerates the flow to smooth the stream-wise velocity component.
The test section has a height of 600 mm, a width of 400 mm and a length of 1500 mm. The lower, the upper and one lateral side of the test section are made of glass to apply optical measurement techniques like Particle Image Velocimetry (PIV). A vane anemometer is used to control the speed of the flow in the test section. The flow uniformity in the test section is determined using a Prandtl probe, which is traversed in 3 cross sections. The measured velocity variations in the core flow are 1% at 10 m/s. The turbulence level measured along the vertical symmetry axis of the test section is less than 0,1% at 10 m/s.
The wind tunnel is intended for research in low-Reynolds- number and unsteady aerodynamics. Standard measurement techniques such as pressure measure-ments are available. Various PIV techniques can be installed. These are Stereo-scopic-PIV, Multiplane-PIV and Time-Resolved-PIV. These allow detailed flow investigations of laminar separation bubbles and the interaction of coherent flow structures in turbulent boundary layers. Experiments on flapping wings at low Reynolds numbers have been done using an in-house designed and built moving model-support.