Among several wind farm layout design parameters, the inter-turbine spacing, which has a great influence on aerodynamic power output, wind speed deficit, lifetime, wake vortex structure, is one of the most critical factors. Therefore, the effects of inter-turbine spacing on aerodynamics for wind farms must be carefully studied. In this study, Considering the uniform inflow conditions, the effects of inter-turbine spacing changing from three to nine times of rotor diameter on aerodynamics for wind farms containing two NREL 5MW baseline wind turbines in tandem layout are analyzed using actuator line model and CFD method, and the RANS equation with k-ω SST turbulence model was solved in the simulations conducted in the OpenFOAM. From the study, it is concluded that the inter-turbine spacing has significant effects on the aerodynamic power and wake characteristics. The aerodynamic power output of the downstream wind turbine exits sharp fluctuation before power output of the downstream wind turbine is becoming steady. Furthermore, periodic oscillation whose period is about the one-third of rotor rotating period can be also concluded from the study. Moreover, there is strong wake interaction which will impact the aerodynamics for wind farms seriously.
Wind energy is a promising renewable energy resource to help handle the environmental pollution caused by the extended use of fossil fuel. Wind farms, which have large capacity to contain plenty of wind turbines, are becoming the main electrical energy source. Since the broader application of wind energy, the layout design of wind farm is becoming significant (Chio, 2014). The layout design of wind farms that affects the initial investment cost, annual energy production, operation and maintenance cost during the service lifetime of wind turbines is a key factor (Kusiak, 2010). Among several wind farm layout design parameters, the inter-turbine spacing, which has a great influence on aerodynamic power output, wind speed deficit, lifetime, wake vortex structure, is one of the most critical factors. We can know that, if the distance between two turbines is too small, there will be seriously effects on downstream turbines due to the strong wake interference, which will cause immeasurable drop of power output and stand higher loads on turbines experiencing wakes compared to those experiencing free stream flows (Barthelmie, 2009). Therefore, the effects of inter-turbines spacing on aero-dynamics for wind farms must be carefully considered to fully study the aerodynamic power out, the wake characteristics and axial speed deficit, specially the wake interaction phenomenon.