Supervisorer: Forsker Sergio González Horcas, DTU Vindenergi - Seniorforsker Athanasios Barlas, DTU Vindenergi
Eksaminator: Assistant Professor Mahdi Abkar, Aarhus Universitit
Titel: Investigating the impact of blade design parameters on blade stability using CFD
Blade vibrations is one the critical areas of blade design as they can gravely affect blade performance and durability. Modern large scale wind turbine blades experience different kinds of vibrations in their machine lifetime and therefore need to be designed so that their structural integrity and performance are not compromised. In the case of a power or control system failure, the rotor is not oriented to face the wind, as the yaw tracking system fails to follow the wind direction, resulting in extreme yaw misalignment. This can lead to extreme angles of attack where the flow is completely separated over the entire blade span leading to the occurrence of vortex induced vibrations in the edge-wise direction. To approach this problem, a CFD method to predict vortex induced vibrations and investigate the impact of the design parameters on blade stability using 1-way Fluid Structure Interaction with imposed blade vibrations is developed.
Unsteady RANS simulations are performed on a stiff non-moving blade for the determination of the of vortex shedding frequency and imposed vibration simulations are performed for the investigation of blade stability. The simulated blade is the offshore 10MW IEA blade. The method was able to complete simulations of non-moving blade predicting the generation of von-Karman vortex street for cases where the flow direction is perpendicular to the pressure side of the blade (0° flow inclination angle). The CFD approach was unable to simulate cases with other inflow angles revealing the limitations of the CFD setup and the design of the computational domain. Such flow angles are necessary for the occurrence of vortex induced vibrations. Imposed vibration simulations with amplitudes up to 0.5 m were completed for inflow velocities with 0° flow inclination angle. The impact of design parameters was studied by manually adjusting the coupling between the edge-wise and flap-wise deflection and using the new mode-shape in imposed vibrations simulations. Aforementioned study revealed a positive impact on blade stability when the coupling is increased.