Research On Single Wind Turbine Far Wake CFD Model

The wake of upstream wind turbine has a serious impact on the performance of downstream wind turbines. Specifically, upstream wake causes the increase turbulence intensity of downstream flow and decline of wind speed, which may lead to high rise of fatigue load of blades and decrease of output power. And accurate far wake model definitely can make wind resource assessment more precise and power grid dispatching flexible. As a result, this paper is aiming at mathematical modeling and simulation analysis:In the aspect of mathematical modeling, due to the restriction of efficiency, analytical model plays a significant role in this field. With the development of computation technology, the Computational Fluid Dynamics (CFD) is prevalent nowadays. However, for improve efficiency; these engineering CFD models are all based on rigid assumptions, such as the assumption of near wake flow field and absence of pressure item, which lower the adaptability of them. In order to resolve this problem, the calculation of near wake flow field should be seriously considered. Aiming at this problem, the work of this thesis is as follows:Firstly, based on the assumption of uniform inflow, flat terrain and actuator disc principle, the deduction of flow field symmetry was acquired. Thus, the dimension of fluid dynamics equations can be reduced, and a one equation turbulence model was employed to simulate turbulence effect. By using vortex and stream function method, a new form of equations is determined in cylindrical coordinates.In the aspect of simulation analysis, the method to calibrate length scale of turbulence, the most important parameter in this model, was determined. A numerical model of equations mentioned above was established by Matlab programming. Secondly, on the foundation of the numerical model above, the changing rate of length scale of turbulence was calibrated to be0.025. The precision of this model is compared with tritional analytical models. It can be easily found that this numerical model maintain a high accuracy, which is above90%and is much higher in the far wake region. Lastly, as this model was a dynamic model, as a result, it was used to simulate the formative procedure of far wake and its impact on the output of downstream wind turbine. Low frequency fluctuation of output power can be generated by wind turbine wake.