Determination of aerodynamic and aeroelastic properties of wind turbines and their support structures through wind tunnel measurements

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023
Wind energy is one of the main contributors to the worldwide transition towards renewable energies. To increase the generation capacity, wind turbine rotors and towers have become increasingly larger, making modern wind turbines highly sensitive to aerodynamic and aeroelastic effects. Some of these effects, especially those acting on tubular steel towers, have been studied in this thesis through wind tunnel measurements.Firstly, the tower along-wind aerodynamic damping has been determined using the forced oscillations method. Surface roughness modification techniques have been used to reduce Reynolds number scale effects. The aerodynamic damping has been determined in wind tunnel tests, applied in a study case, and described analytically. Its relevance is limited to parked conditions and extreme wind speeds. For the first time, the forced oscillations method has been used to determine the aerodynamic damping of wind turbine rotors and their blades, and the results have been proved to reflect the predictions from multi-body simulations and well-known analytic approaches from the literature. The methodology, equations and scaling laws required for wind tunnel measurements of wind turbine models using the forced oscillations method have been developed and documented in detail.%It is concluded that the forced oscillation method can be used for the determination of the aerodynamic damping of wind turbines.Secondly, the characteristics of vortex-induced vibrations in parked wind turbines have been studied using an aeroelastic wind tunnel model, and the most critical rotor positions have been identified. For some configurations, the measurements show VIV occurrences at Strouhal numbers around St=0.14 or at two different Strouhal numbers, being this a singularity of parked wind turbines. The results have been applied to a study case, and a reduction of VIV amplitudes due to rotor blade disturbances has been observed in most cases.Finally, the blade passing effects on the wind turbine tower aerodynamics have been determined in wind tunnel measurements for one operation state. The resulting tower aerodynamic coefficients have been averaged for one blade passing and given at five tower heights for its implementation in multi-body-simulations. The blade passing effects have been quantified in a study case. A light reduction of the average along-wind tower base moment, an increase of the average and RMS cross-wind tower base moments, and a small increase of the estimated fatigue damage is observed near the cut-of speed.
Published by RWTH Aachen University, Aachen