New Models for Flutter and Edgewise Instability Analysis of Vertical and Horizontal Axis Wind Turbines for Land-based and Floating Offshore Conditions


August 2023


Journal Title

Journal ISSN

Volume Title



Wind energy is a vital part of renewable energy sector that is increasingly becoming popular to reduce the adverse effect of traditional power production methods in increasing the global temperature. As the demand for wind energy increases, the sizes of the blades of wind turbines are also increasing with the availability of novel materials and manufacturing techniques. On the other hand, these very large wind turbines might be susceptible to design challenges and instability problems because of their sheer size which typically are not concerns for relatively smaller turbines. This has motivated the development of models to predict the unstable behavior of very large vertical axis wind turbines (VAWTs) and horizontal axis wind turbines (HAWTs). This work presents modeling method of rotor-platform system for offshore floating vertical axis wind turbines. Effect of structural design parameters on flutter instability of 2-bladed and 3-bladed VAWTs are studied. An analysis is presented on the effect of floating platform on flutter behavior of rigid body and flexible modes of vibration of the coupled system. A fundamental understanding of how the floating system impacts the resonance and flutter properties of VAWT is sought and presented. Further study has been performed on the impact of aerodynamic modeling assumptions that are conventionally implemented to predict flutter of wind turbines. The shortcomings of simplifying assumptions of standard aerodynamic theory have been demonstrated, and new aerodynamic model is developed to address those shortcomings. Then, this new model is applied to both horizontal axis wind turbines as well as vertical axis wind turbines. Comparative analysis is done of the effect of standard and new aerodynamic model in terms their predictive capability of flutter for both land-based and floating vertical axis wind turbines. Large number of horizontal axis wind turbines with varying sizes and geometry are studied for flutter and edgewise instability with the newly developed aerodynamic model. Similarly, vertical axis wind turbines are examined with the newly developed aerodynamic model. This study also aims at validating numerical models with experimental results. To achieve that goal, a subscale floating VAWT system is manufactured, and experimental test is performed on it to extract modal dynamic properties. The measured structural properties are used to calibrate the rotor model, and free decay test results are used to generate a floating platform model. Finally, the rotor and platform model are coupled and modal analysis (frequency analysis) is performed and the model is further refined by comparing the test results and model predictions. Key findings of this dissertation confirm that moving a VAWT from land-based to floating configuration has the potential to alleviate both resonance and flutter concerns. Developed new aerodynamic model shows higher flutter prediction of tower, propeller and edgewise modes of land-based and floating VAWT compared to the prediction by standard aerodynamic model. For large HAWT blades, the new aerodynamic model has more impact on 3-bladed case than on 2- bladed case in terms of flutter and edgewise instability RPM prediction. Validation study on modal dynamics of floating VAWT confirm reasonably accurate modeling of coupled rotor-platform floating model.



Engineering, Mechanical