This paper presents an experimental investigation into the aeroelastic behavior of an innovative wind turbine design featuring a downwind two-blade rotor with a teetering hub mounted on a tower with adjustable tilt. The rotor model incorporates two sets of elastic blades—stiff and flexible—for scaling purposes, each instrumented with strain gauges and accelerometers. Ground and wind tunnel tests were conducted to analyze the aeroelastic response. Static tests exhibited discrepancies between measured and numerically predicted displacements, with maximum displacements near the tip exceeding numerical predictions by 14% and 31% for flexible and stiff blades respectively. Frequency differences between measured and numerically simulated elastic modes ranged from 0.5% to 18% for both blade sets, as determined by ground vibration tests. Wind tunnel tests revealed the dominance of rotational speed harmonics, particularly the second harmonic, in the blades’ periodic response. A sensitivity analysis was also carried out with respect to tower tilt angle, rotational speed and blade pitch angle, for both blade sets at a range of tip-speed ratio values. The static response of the system, as captured by the generated power and thrust, was primarily sensitive to tower tilt angle variation and to a lesser extent blade pitch angle. Conversely, the tip-speed ratio in conjunction with rotational speed were found to dictate the dynamic response, influencing the azimuthal position and magnitude of the maximum bending moment at the blade root. Finally, no dynamic aeroelastic instability was observed during wind tunnel tests.

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The present study regards a novel wind turbine design featuring a two-bladed rotor on ate etering hub and a yawed tower. A reduced order modelling methodology is proposed for the equation of motion, using a lumped parameter approximation to derive expressions for the structural, rotor dynamic and geometric stiffness terms. The analytical expressions are validated numerically. In addition, a methodology is developed for aero elastic scaling of the rotor for use in wind tunnel tests. This results in two blade design templates, a "stiff" and a "flexible" design focusing on the vibration behaviour and deflected shapes respectively. The templates are designed to be 3D-printable as a single part. Design optimisation was performed in MSCN as tran, yielding two rotor designs, each aiming to match the non-dimensional parameters of interest. The stiff rotor matches the flap wise and torsional natural frequencies within 2.7%error, but has a mismatch in the edgewise mode, as well as the mode shapes and anti-symmetric modes. The flexible rotor is capable of capturing the target normalised displacement profile, at reduced structural mass, partially alleviating the mismatch in Lock number.

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The idea of the EU funded FLEXOP project is to raise efficiency of a currently existing wing by derivative solution with higher aspect ratio at no excess structural weight. In order to enable such a resulting highly flexible wing the project goal is to develop methods for active suppression of flutter and passive load alleviation. The developed methods will be tested and validated with a UAV flutter demonstrator. The demonstrator is a 7m wingspan, 65kg MTOW UAV equipped with a jet engine. After ground testing, including static load and ground vibration tests the demonstrator will be flown within VLOS with three different sets of wings: One baseline rigid wing, one wing tailored for passive load alleviation and one very flexible wing to test active flutter control. The paper describes the design methods of the demonstrator and gives an overview about the planned tests on ground and in flight to validate the flutter prediction models. A special emphasis is on in flight wing shape measurement with an installed fiber brag system. @en