Developing a Virtual Stiffness-Damping System for Airfoil Aeroelasticity Testing

Development of a two-degrees-of-freedom (2-DOF) virtual stiffness-damping system (VSDS) to facilitate industrial and laboratory testing of airfoil aeroelastic instability (AAT) is presented in this paper. Development and use of existing test-beds are costly due to involvement of physical springs to simulate airfoil elasticity. Although replacing physical springs with a VSDS has been used in other fields such as marine and biomechanics engineering, existing VSDSs cannot be directly used for 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 proposing direct force/torque regulation with force/torque feedback. Secondly, resolution loss in velocity measurement is identified as a main problem associated with the non-reduction transmission required and is solved by proposing a modified extended-state observer (MESO) for fast velocity estimation. Thirdly, system identification and calibration procedures involved in developing the new VSDS is reduced to minimum by applying a robust force/torque tracking controller. 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.