Aeroelasticity of Wind Turbines Blades Using Numerical Simulation

With roller coaster traditional fuel prices and ever increasing energy demand, wind energy has known significant growth over the last years. To pave the way for higher efficiency and profitability of wind turbines, advances have been made in different aspects related to this technology. One of these has been the increasing size of wind turbines, thus rendering the wind blades gigantic, lighter and more flexible whilst reducing material requirements and cost. This trend towards gigantism increases risks of aeroelastic effects including dire phe‐ nomena like dynamic stall, divergence and flutter. These phenomena are the result of the combined effects of aerodynamic, inertial and elastic forces. In this chapter, we are present‐ ing a qualitative overview followed by analytical and numerical models of these phenomena and their impacts on wind turbine blades with special emphasize on Computational Fluid Dynamics (CFD) methods. As definition suggests, modeling of aeroelastic effects require the simultaneous analysis of aerodynamic solicitations of the wind flow over the blades, their dynamic behavior and the effects on the structure. Transient modeling of each of these char‐ acteristics including fluid-structure interaction requires high level computational capacities. The use of CFD codes in the preprocessing, solving and post processing of aeroelastic prob‐ lems is the most appropriate method to merge the theory with direct aeroelastic applications and achieve required accuracy. The conservation laws of fluid motion and boundary condi‐ tions used in aeroelastic modeling will be tackled from a CFD point of view. To do so, the chapter will focus on the application of finite volume methods to solve Navier-Stokes equa‐ tions with special attention to turbulence closure and boundary condition implementation. Three aeroelastic phenomena with direct application to wind turbine blades are then stud‐ ied using the proposed methods. First, dynamic stall will be used as case study to illustrate