Flight Dynamics Wind Tunnel
The Flight Dynamics Group operates the 2-by-2 meter low-speed wind tunnel L2000 using modern digital measurement equipment for both research and graduate education. Experiments usually involve moving and deforming wind tunnel models or unsteady flow phenomena.
L2000 is a closed-circuit low-speed wind tunnel build in the 1960's in connection with the design of the Saab Viggen fighter aircraft. When the flight dynamics division took over the tunnel in 1996, hardware and instrumentation were substantially upgraded and modernized. Equipment currently in use include, for example, two six-component internal model balances, a networked unsteady pressure measurement system, a wake-rake, high frame-rate video cameras and an ethernet-based embedded servo controller used to actuate control surfaces inside wind tunnel models. All measurements can be timestamped with GPS time in order to allow accurate correlation of unsteady force, pressure and motion measurements.
Many research projects of the division concern aeroelasticity and flight mechanics, and as a result, experiments perfomed in the L2000 often require accurate tracking of unsteady model movements and deformation along with more traditional measurements of forces and moments. For this purpose, the wind tunnel is equipped with an optical motion tracking system which allows to measure the position of small reflecting markers mounted on wind tunnel models with very high frame rates.
Use in Education
L2000 is also used in the courses "Experimental aerodynamics" and "Aeroelasticity" of the Aerospace Master program. In the former, students use pressure and force measurements to determine the aerodynamic properties of wind tunnel models such as the one shown below. Furthermore, flourescent oil flow visualization is used in order to investigate the development of the surface friction, from which conclusions about the location of laminar-turbulent transition, or the presence of laminar separation bubbles can be drawn.
In the course on aeroelasticity, a simple, flexible (and fairly tough...) wing model is used to determine the critical flight speed for the onset of flutter and static divergence. Students develop computational models for the wind tunnel configuration and perform mass balancing of the model to achieve desired aeroelastic properties.