Flutter of a Wind Turbine Airfoil

Abstract

In order to be more competitive with conventional, polluting energy resources, the levelised cost of energy (LCoE) of wind turbines has to decrease significantly [1]. A method to achieve this goal is to reduce the amount of parts in a wind turbine and more specifically avoid the use of expensive and failure-prone pitch systems. Using blades which passively deform under high aerodynamic loading and effectively reduce the peak, design-driving loads on the turbine structure might offer an interesting alternative to the pitch system. However, the conventional material for construction of blades, glass-fibre reinforced plastics,
does not allow for such large deformations during normal operating conditions. Prior to this project, a study to incorporate more flexible materials has been carried out in the design of the current XANT-21 wind turbine in order to increase the flexibility of the blades. However, introducing a high degree of flexibility in the wind turbine blades might increase the risk of aeroelastic instabilities. These aeroelastic instabilities often result, in combination with a non-linearity in the aerodynamics or structure, in limit cycle oscillations (LCOs). The need to identify the key structural parameters which play a role in the initiation of the aeroelastic instabilities has led to the objective of this thesis: Investigate the influence of the critical structural parameters on the onset velocity and the behaviour of high-amplitude limit cycle oscillations of a wind turbine airfoil by means of numerical simulations.