Wind tunnel for Aerodynamic and Acoustic studies WAABLIEF
The WAABLIEF (Wind tunnel for Aerodynamic and Acoustic studies of Boundary Layers Including pressure gradient EFfects) facility design is a revamped version of the VKI L-2A low-speed, suction-type open circuit wind tunnel. It incorporates an air inlet, a circular cross-section settling chamber fitted with honeycomb and meshes, and an axisymmetric 8:1 contraction leading to a (0.25 x 0.25) m2 test section with a length of 2 meters. The axial fan, located at the end of a 1:4 diffuser, is driven by a 9.9 kW variable-speed DC motor, providing a maximum flow velocity of 45 m/s, with a turbulence level of 0.25 %. This facility is especially suited for research projects and laboratory training in turbulent boundary layers, three-dimensional velocity measurements and, with the addition of a smoke generator and of an air exhaust to outside, laser sheet flow visualizations and quantitative optical techniques. A six-component strain gauge platform balance, of pyramidal type, with virtual center located on the tunnel axis, is also available.
The facility has been upgraded by adjoining an acoustic muffler between the fan and the test section, and designing a new test section equipped with a motorized rotatable disk equipped with 64 microphones on its lower wall. This wall-mounted microphone antenna permits the measurements of the boundary layer wavenumber-frequency spectrum, streamwise/spanwise coherence lengths and convection velocities, and to correlate those quantities with flow measurements performed by means of hot wire anemometry, Laser Doppler Velocimetry and Stereoscopic Particle Image Velocimetry. Favorable or adverse pressure gradients are prescribed by replacing the upper wall of the test section with converging or diverging ramps.