Application of frequency-domain system identification to wind tunnel experiments on the Active Aeroelastic Test Bench

The design of an aircraft requires a very expensive and lengthy certification process. Within this certification process manufacturers use both wind tunnel tests, as well as in-flight test to ensure structural integrity for the service life of the aircraft. Advanced processing techniques are required due to the challenging environmental conditions, high noise levels, varying test conditions and nonlinear behaviour of both the airflow and the structure. In this thesis a novel type of actuated wind tunnel test setup is designed and installed in the wind tunnel of the Vrije Universiteit Brussel. The Active Aeroelastic Test Bench (AATB) allows to subject a wing to arbitrary oscillations in vertical plunge and rotational pitch motion. Two types of experiments can be performed with the AATB. Firstly, with a rigid wing supported at both extremities, the resulting aerodynamic forces from the forced motion in pitch and plunge can be studied. Secondly, using a flexible cantilever wing, it is demonstrated how the combination of the AATB and recently developed frequency-domain system identification techniques allows to quantify the level of nonlinearity in the observed response. Additionally, uncertainty bounds are estimated for all experiments, such that significant changes in the response at different operating and test conditions can be detected. Finally, in an attempt to further reduce the required testing time, it is demonstrated how the use of system identification tools for time-varying test conditions can reduce the required wind tunnel test time even further by a factor of almost ten, and this without sacrificing accuracy.