4 research outputs found
Model-based displacement estimation of wind turbine blades using strainmodal data
For wind turbine rotor blades, the use of strain sensors is preferred over acceleration sensors for the purpose of permanent monitoring. Experimental modal analysis during operation is thus constrained to strain information, yielding strain modal data including strain mode shapes. For follow-up investigations such as aerodynamic load assessment or flutter monitoring it is however advantageous to have this information as displacement mode shapes or as displacements of the blade contour over time. This research applies a generic approach that converts strain mode shapes to displacement mode shapes utilizing an FE shell model as a basis for approximation. The accuracy of the approach is assessed by comparison with experimentally identified high-resolution displacement mode shapes which are acquired with accelerometers and serve as a reference. In the process the conversion procedure is illustrated with the help of strain data that has been obtained using a sensor instrumentation installed for certification testing of the blade. The requirements for successful usage of the employed conversion scheme and its suitability for rotor blade data are discussed
A systematic investigation of common gradient based model updating approaches applied to high-fidelity test-data of a wind turbine rotor blade
Within the context of the "SmartBlades2"-project, a wind turbine rotor blade was designed and extensively tested. The rotor-blade uses a lightweight composite structure and bend-twist coupling. The bend-twist coupling facilitates a passive load-reduction by changing the angle of attack under load.
Due to a high sensor-density of 265 accelerometers in the experimental modal test of the blade, the sophisticated structural dynamics of the model are captured. Apart from the commonly measured first flapwise-, edgewise-bending and torsion mode, 35 modes up to a frequency of 60 Hz are identified. Unlike in many other wind turbine rotor blade investigations, the Finite Element (FE) model uses shell elements instead of beam elements and is directly based on production drawings. This experimental and simulative setup is particularly relevant, since a significant number of mode shapes exhibit a distinct local behavior which was in previous studies not accounted for.
The differences between experimental and simulated results are minimized using computational model updating procedures. In this case-study, two formerly underrepresented aspects of the updating of large-scale FE models are examined. One is the use of different parameterizations and the other is the possibility of insufficient experimental data. The parametrizations are based on well-established criteria like error-localization and sensitivity. Moreover, the updating is performed with different (i.e. reduced) subsets of the modal data and the results are then compared to the model updating results achieved with the entire dataset. This in-depth investigation of the model updating of a composite structure allows the deduction of general guidelines in the model updating of industrial-sized FE models
Measurements of deformation, schlieren and forces on an OAT15A airfoil at buffet conditions
Self-sustained shock wave oscillations on airfoils, commonly defined as shock
buffet, can occur under certain combinations of transonic Mach number and angle of attack due
to the interaction between the shock and the separated boundary layer. To help understanding
buffet physics, a rigid supercritical wing model (OAT15A) was investigated in pre-buffet and
buffet conditions using a combined application of BOS (Background Oriented Schlieren),
deformation and force measurements. From the observation via BOS of the change of the
shock location and the extent of the boundary layer separation with the AoA (angle of attack),
the transition from stable shock to buffet was detected. A comparison with other research
groups at supposedly similar aerodynamic conditions highlighted a great disparity among them
in terms of buffet onset, amplitudes of buffet oscillations, and flow development (motion of the
mean shock location with the AoA) after the onset. The average and rms (root mean square) of
the surface displacement were computed together with the effective geometric AoA, taking
into account the static torsional deformation of the model and its support. Moreover, the
spectra of the balance and deformation data showed the same buffet peak as in the BOS
spectrum, indicating a coupling between structure and flow, which increased with the AoA
German research wind farm WiValdi: Planning, installation and testing of innovative research instrumentation for six wind turbine rotor blades
Together with the partners from the German Research Alliance the German Aerospace Center is building the German research wind farm WiValdi (Wind Validation). The wind farm will consist of two standard wind turbines of type E-115 EP3 E4 and a smaller custom build research turbine. The setup of the wind farm is supported by national funding in the research project DFWind.
Within DFWind the wind turbine rotor blade research instrumentation has been planned, installed during manufacturing and tested during rotor blade tests at IWES in Bremerhaven. The research instrumentation covers various fields of research from aeroelasticity, structural dynamics, structural health monitoring, vibroacoustic to loads and control. Different types of sensors and measurement systems have been integrated. The sensors vary from classical acceleration sensors over fiber optical acceleration, strain and temperature sensors to innovative continuous fiber optical strain sensors, ultrasonic sensor arrays and finally markers for digital image correlation from inside the blade and on the outer surface.
The presentation will give insights in the sensor planning and testing, the instrumentation campaign during manufacturing process and the rotor blade tests before installation on the turbines