A rapid development has been made in the global wind power industry since the 90s of last century, with the constantly increasing of wind power installed capacity and enlarging of the wind turbine rated power and leaf size. Until the end of 2012, the rated power of the largest single wind turbine in operation had reached 7.58 MW, the maximum wind wheel diameter reaching 154 m. The trend of large-scale wind power blade makes the study of fatigue problem more and more important.
One characteristic of fatigue load lies in the fluctuation, which is mainly caused by turbulence, tower shadow effect, wind shear and other unsteady effect. Because of the high performance, good structure and safety characteristics, trailing edge flaps can be applied in the wind turbine easily and is considered as the most feasible pneumatic control components to reduce wind turbine blade fatigue load.
Researchers from Sandia National Laboratory, USA, Delft Polytechnic University, Holland, and Ris ø DTU, Denmark have conducted many research on wind turbine airfoil with trailing edge flaps, showing that the trailing edge flaps had a good effect on load reduction. However, the related researches were mainly concerned with the control strategy, aero-elastic and implementation methods. Little research were made on flow state near the trailing edge flaps, and gas dynamic in aero-elastic analysis were mainly solved in the quasi-steady method, ignoring the effect of unsteady characteristics of flap motion.
With the steady and unsteady computational fluid dynamics method, researchers from IET studied the aerodynamic characteristics of trailing edge flap and analyzed its influence on the flow structure and mechanism. The regulation of trailing edge flaps can reduce the change of flow rate caused by load variation, thereby reducing the fatigue load, which provides some reference for optimization of trailing edge flaps application, control law, and lays a basis for revising simulation of trailing edge flaps and other control components in blade element-momentum theory.
Recently, researchers got the relationship between the optimizedparameters of wind turbine airfoil trailing edge flaps and relative size of different factors, analyzed its dynamic properties, and pointed out factors for adjustment according to specific circumstances. Besides, the reduced frequency, which took the length of trailing edge flaps as characteristic scale, was also proposed as new criteria for unsteady characteristics of trailing edge flaps. The simulation research of wind turbine blade dynamic trailing edge flaps with the unsteady computational fluid dynamics method provided reliable guidance for control of turbine fatigue load. In addition, the analysis of dynamic characteristics for the 3D wind turbine blade trailing edge flap showed that the influence of motion characteristics of wind turbine blade trailing edge flap were not limited to the near trailing edge flaps, but covering almost the entire leaves and being of distinct 3D characteristics. The traditional blade element-momentum theory needs correction.
