Room:
Diesel Hall
Topic:
C. Aeroservoelasticity, loads, structures and materials
Form of presentation:
Oral
Duration:
100 Minutes
Chaired by: G. van Kuik, M.H. Hansen
11:30
Aeroelastic Stability of Idling Wind Turbines
Prof. Vasilis Riziotis | National Technical University of Athens | Greece
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Authors:
Prof. Vasilis Riziotis | National Technical University of Athens | Greece
Spyros Voutsinas | Greece
Kai Wang | Greece
Wind turbine rotors in idling operation mode can experience high angles of attack, within the post stall region that are capable of triggering stall-induced vibrations. In the present paper rotor stability in slow idling operation is assessed on the basis of non-linear time domain and linear eigenvalue analysis. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First the flow conditions that are likely to favour stall induced instabilities are identified through non-linear time domain aeroelastic analysis. Next, for the above specified conditions, eigenvalue stability simulations are performed aiming at identifying the low damped modes of the turbine. Finally the results of the eigenvalue analysis are evaluated through computations of the work of the aerodynamic forces by imposing harmonic vibrations following the shape and frequency of the various modes. Eigenvalue analysis indicates that the asymmetric and symmetric out-of-plane modes have the lowest damping.
11:50
Field Validation of the Stability Limit of a Multi MW Turbine
Dr. Knud Abildgaard Kragh | Siemens Wind Power | Denmark
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Authors:
Dr. Knud Abildgaard Kragh | Siemens Wind Power | Denmark
Knud Kragh | Denmark
Long slender blades of modern multi-megawatt turbines exhibits a flutter like instability at rotor speeds above a critical rotor speed. Knowing the critical rotor speed is crucial to a safe turbine design. The flutter like instability can only be estimated using geometrically non-linear aeroelastic codes. In this study, the estimated rotor speed stability limit of a 7 MW state of the art wind turbine is validated experimentally. The stability limit is estimated using Siemens Wind Powers in-house aeroelastic code, and the results show that the predicted stability limit is within 5% of the experimentally observed limit.
12:10
Experimental and operational modal analysis of the laboratory scale model of the tripod support structure.
Dr. Marcin Luczak | Institute of Fluid-Flow Machinery, Polish Academy of Sciences | Poland
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Authors:
Dr. Marcin Luczak | Institute of Fluid-Flow Machinery, Polish Academy of Sciences | Poland
Emiliano Mucchi | Poland
Janusz Telega | Poland
The goal of the research is to develop a vibration-based procedure for the identification of structural failures in a laboratory scale model of a tripod supporting structure of an offshore wind turbine. In particular, this paper presents an experimental campaign on the scale model tested in two stages. Stage one encompassed the model tripod structure tested in air. The second stage was done in water. The tripod model structure allows to investigate the propagation of a circumferential representative crack of a cylindrical upper brace. The in-water test configuration included the tower with three bladed rotor. The response of the structure to the different waves loads were measured with accelerometers. Experimental and operational modal analysis was applied to identify the dynamic properties of the investigated scale model for intact and damaged state with different excitations and wave patterns. A comprehensive test matrix allows to assess the differences in estimated modal parameters due to damage or as potentially introduced by nonlinear structural response. The presented technique proves to be effective for detecting and assessing the presence of representative cracks.
12:30
Trailed vorticity modeling for aeroelastic wind turbine simulations in standstill
Georg Pirrung | DTU | Denmark
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Authors:
Georg Pirrung | DTU | Denmark
Helge Madsen | Denmark
Scott Schreck | Denmark
Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A trailed vorticity model previously used as addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill. The model is validated against analytical results for an elliptical wing in constant inflow and against stand still measurements from the NREL/NASA Phase VI unsteady experiment. The extended model obtains good results in case of the elliptical wing, but underpredicts the steady loading for the Phase VI blade in attached flow. The prediction of the dynamic force coefficient loops from the Phase VI experiment is improved by the trailed vorticity modeling in both attached flow and stall in most cases. The exception is the tangential force coefficient in stall, where the codes and measurements deviate and no clear improvement is visible.
12:50
High fidelity CFD-CSD aeroelastic analysis of slender bladed horizontal-axis wind turbine
Mohamed Sayed | Universität Stuttgart | Germany
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Authors:
Mohamed Sayed | Universität Stuttgart | Germany
Thorsten Lutz | Germany
Ewald Kraemer | Germany
Shahrokh Shayegan | Germany
Aditya Ghantasala | Germany
Roland Wüchner | Germany
Kai-Uwe Bletzinger | Germany
The aeroelastic response of large multi-megawatt slender horizontal-axis wind turbine blades is investigated by means of a time-accurate CFD-CSD coupling approach. A loose coupling approach is implemented and used to perform the simulations. The block-structured CFD solver FLOWer is utilized to obtain the aerodynamic blade loads based on the time-accurate solution of the unsteady Reynolds-averaged Navier-Stokes equations. The CSD solver Carat++ is applied to acquire the blade elastic deformations based on non-linear beam elements. In this contribution, the presented coupling approach is utilized to study the aeroelastic response of the generic DTU 10MW wind turbine. Moreover, the effect of the coupled results on the wind turbine performance is discussed. The results are compared to the aeroelastic response predicted by FLOWer coupled to the MBS tool SIMPACK as well as the response predicted by SIMPACK coupled to a Blade Element Momentum code for aerodynamic predictions.