Numerical Simulation Of Fluid Structure Coupling Of Wind Turbine Blades

In order to absorb more wind energy, wind turbines become larger and larger, the blades become slender and more flexible. Wind turbines often operate in the stochastically changed natural atmosphere, which would lead to load fluctuations on the rotor blades. Consequently, coupling effects of variable loads on the flexible structure will easily induce unavoidable deformation and vibration of the rotor structure. In addition, for low cost of wind power, new type wind turbine blades were developed base on the study methods of aeroelastic characteristics, which need to consider the coupled effects of the aerodynamic, elastic and inertia force together. Therefore, it is very necessary to establish accurate and reliable methods to analyze fluid-structure coupling effects of wind turbine rotors, and to better reveal the interaction between aerodynamic loads and the structural deformations, for the blades design and Analyze, which has important practical meaning in project.In fluid domain, steady and unsteady aerodynamic characteristics is the foundation of the fluid-structure coupling characteristics of airfoils and wind turbine blades. Firstly, with a view of the attack angle of section airfoil, the analyse of the influences of the attack angle variation in0～360°range of2D airfoils, and by the blade profile modification were carried out. Oscillating movements of the airfoils could also cause the local attack angle variation. Moreover, complex motion can be regarded as the superposition of simple movements, therefor, the study of the unsteady aerodynamic characteristics of oscillating airfoil in particular forms is the basis of the fluid-structure coupling characteristics of wind turbine blades.In loosely coupled approach, the fluid and structure equations are solved separately using different solvers and the information exchanged at the interface or the boundary. This approach gives us the flexibility of choosing different commercial codes for each of the modules. Therefore, we employ MpCCI code as a loosely coupled data exchanging platform, which coupling commercial CFD and CSD codes. On the basis of the verification of the coupling approach through the standard example of AGARD445.6flutter boundary simulation, a full3D fluid-structure coupled simulation of a megawatt wind rotor in different wind speed condition is performed, and the results reveal that:The performance parameters of the fluid-structure coupling simulation show periodic oscillation, and the oscillation amplitudes decrease rapidly and converge to a stable value. When the inflow speed is lower than the rated wind speed, fluid-structure interaction has little effects on the blade power. If the inflow exceeds the rated wind speed, the fluid-structure coupling power value decreases significantly. The thrusts are the same. Fluid structure interactions effect the local attack angle, the pressure distribution of the section airfoils and the loads distribution along the whole blades. The displacements in the flapwise, edgewise and spanwise direction show the first order shape, that large at root and small at tip. In the case of high wind speed, flapwise deformation decreases while edgewise grow larger. Stress focus at the middle section along blade span, and maximum thickness position chordwise. Maximum stress presents at the rated wind speed.Furthermore, fluid structure coupling characteristics of wind rotor in shear inflow condition is studied. Comparison of the variable wind speed, the shear inflow effects, and the interaction of the blades deformation and the shear inflow effects show that:Due to wind shear inflow, the aeroelastic loads keep the same characteristics to aerodynamic loads as the decrease in value due to the average wind speed decrease, and the3p pulsation in loads in a rotating circle, flow parameters of one blade present as a cosine curve in a rotating circle. the up-down asymmetric characteristic appears in the rotating plane because of the wind shear inflow. For the coupling effects, the performance parameters show periodic oscillations, fluid structure coupling has little effect on the periodic oscillations and their amplitude. Blade torsion decreases at inner span, while loads increase, and the outer part of the blades is on the contrary. The tangential and normal force extreme values are not corresponding to the wind speed extreme values, and the spanwise distributions are quite different between the aeroelastic and aerodynamic loads mainly due to the torsion of the blades.