Developing a virtual stiffness-damping system for airfoil aeroelasticity testing

In this research a two-degrees-of-freedom (2-DOF) virtual stiffness-damping system (VSDS) is developed to facilitate industrial and laboratory testing of airfoil aeroelasticity instability. Other existing test-beds in this field rely on elastic elements or structures to set airfoil elasticity in tests, which can be costly and inconvenient in cases of frequent stiffness adjustment across a wide range. A possible alternative is the VSDS that utilizes electric drives to simulate structural elasticity and damping, as seen in marine and bio-mechanical engineering, which however, cannot be directly applied to airfoil aeroelasticity testing (AAT) due to operation requirements and conditions being different. Therefore, in this study a new VSDS is developed specifically for AAT. Firstly, the concept of 1-DOF VSDS is extended to 2 DOFs, with the dynamics coupling between each DOF addressed at the stage of operation principle determination, by the proposed direct force/torque regulation with force/torque feedback. Secondly, resolution loss in position/velocity measurement is identified as a main problem associated with the non-reduction transmission required, and is solved by a modified extended-state observer (MESO) proposed for fast position/velocity estimation. Thirdly, system identification and calibration procedures involved in developing the new VSDS are reduced to minimum through a robust force/torque tracking controller design, with detailed numerical study on parametric analysis given. As validated in wind-tunnel experiments the new VSDS can closely track the desired force/torque and provide satisfactory virtual stiffness and damping in AAT.