A Novel Approach for Staggered Fluid-Structure Interaction Simulation of Shape-Adaptive Airfoils for Wind Turbine Rotor Blades

Abstract

With the increase in demand on renewable energy, the modern horizontal axis wind turbines have already reached a stage with considerabely large rotor blades. With the current rotor diameter of 150 m and taking into consideration the growing emphasis on offshore wind turbines, the trend suggests a continuing increase in rotor diameter for future wind turbines. This imposes a trade-off between the energy production and the controlability of the system. The increase in rotor diameter results in higher torque requirement on the active pitch/stall-control motor. Moreover, it is difficult to achieve optimal inflow condition over the entire span length for the rigid blades. This results in high structural loading, which in turn reduces the lifespan of the blades. In light of this situation, local airfoil form-adaption promises to be an alternative control scheme for future wind turbines. By allowing the provision for flow control locally, faster and much more detailed control of aerodynamic loading would be possible. The shape adaption strategy of the future wind turbine blades depends on the simulating capability of the coupled fluid-structure interaction for the blade. In the field of aviation, fluid-structure interaction (FSI) is of growing interest, and numerical schemes are being developed to simulate the coupled fluid and structural dynamics of different aerodynamics components. In turbomachinery, recent attempts have been directed in the simulation of fluid-structure interaction Viz. blade flutter, dynamic stall. The authors present a novel approach to simulate the fluid-structure interaction for a shape-adaptive wind turbine blade. The interaction between fluid and structure is assumed to be of a static type. The coupling is taken to be of a staggered kind. The aerodynamic simulation is carried out with the help of a low order simulation code XFOIL. The structural simulation is carried out with the help of the finite element program CalculiX. The open-source mesh generator NETGEN is used to discretize the blade geometry into an unstructured mesh, which is then automatically read into CalculiX via a script. Numerical routines are developed to transfer information between the fluid and the structure solver. This approach results in a significant reduction in the numerical effort and the simulation time, and thus allows one to simulate the fluid-structure interaction with minimum user input. Moreover, this will allow us to carry out early conceptual development of different actuation systems to achieve the shape adaption of the wind turbine blade airfoil.