Wake interaction normally occurs in all wind farms and impacts significantly the flow field and performance of downstream wind turbines. The present work aims to study the wind turbine wake interaction phenomenon through the CFD method using LES and actuator line model. The solver used in the present work is developed based on the open source C++ class library OpenFOAM, in which the PISO algorithm is applied to deal with the velocity pressure coupling problem. The simulations which consider uniform inflow condition and six different layouts are implemented to study the evolving process of the interacting wakes. From the numerical result, the interacting region of wakes contains higher level turbulent flow than the single wake. The fully developed turbulence appears the earliest in the case of tandem layout, leading to serious wake meandering in the end of computational domain. The diffusion of turbulence causes the merging of wakes, and thus the velocity is redistributed among the whole wake region. Velocity deficit caused by the wake decreases the convertible wind energy. The turbulent flow and meandering of the wake result in the multi-scale fluctuation of the aero-power curves of wind turbines downstream.
Benefiting from the rapid development of wind turbine technology in recent years, the number of wind farms putted into operation keeps increasing. As one of the most concerned problems in the wind energy industrial, wake effect occurs widely in all wind farms, which could not only result in a sharp reduce in the total power production but also cause a considerable increase of the fatigue load of wind turbine structure (Vermeer et al., 2003, Troldborg, 2009). The formation of the wake region is due to the basic working principles and characteristics of a wind turbine. When the wind flows to a wind turbine, the blades are pushed by the lift force to rotate around the horizontal low speed shaft. During this process, the wind turbine converts the kinetic energy of the wind into electrical energy though a generator placed in the nacelle and thus inevitably leaves a meandering tube-shaped region behind the rotor, where the wind speed is slowed down and turbulence level is relatively high (Troldborg et al., 2011). Taking into account the limiting factors such as land cost, topography, transportation, power transmission and etc., all the wind turbines of a wind farm must be placed in a fairly limited area, therefore, power losses caused by wake effects cannot be completely avoided. Since the layout of the turbine array apparently has a vital influence on how serious the wake effect will be, we could find out theoretically a reasonable arrangement and thus reduce the losses as much as possible.
