Extensive preliminary investigations to design experiments in the Transonic Wind Tunnel Göttingen were conducted as part of the DLR research project FaUSST. The purpose of the experiments is to investigate the influence of vortex-dominated flow occurring particularly in a high angle of attack range on the aeroelastic stability of a lambda wing configuration. The wind tunnel model featured a configuration based on the F17/SACCON assembly. It was given the name IWEX (unsteady vortex experiment).
The upper image shows the typical vortex system precipitated in the IWEX configuration at a 15-degree angle of attack. The leading edge vortices and the tip vortex are of vital importance to lift distribution across the wingspan. The image in the centre shows the FE model used in the configuration. It shows an exaggerated, steady deformation of the wingtip. Coupled, unsteady calculations applying the DLR TAU code in combination with the PyCSM coupling software were conducted to determine the aeroelastic behaviour. The coupled, unsteady calculations were carried out using a variety of mean angles of attack, angle of attack amplitudes and frequencies in the work described above.
The pressure distributions were measured over two campaigns using unsteady pressure sensors, while piezoelectric sensors recorded global forces and moments. Model deformation was recorded using a marker-based, optical system. iPSP and PIV measurements were also conducted (applied through derivation of experimental techniques used at the Institute of Aerodynamics and Flow Technology). The Mach number for the angle of attack varied between 0.3 – 0.7. The maximum excitation frequency of the pitching oscillations was 22 herz. The measurement focused on the angle of attack between 10 and 20 degrees in which vortex-dominated flow will form.