Numerical Simulation Of Wind Turbine Wake Flow Field

The interactions between wind turbine wakes seriously affect the overall power output efficiencyof the wind farm, so the in-depth study of the development law of wind turbine wakes is of important.Generally computational fluid dynamics (CFD) method is used to get the flow fields about windturbine wakes, but for the need of huge computational resource, it is difficult to simulate the windfarm flow fields with several wind turbines directly. Therefore, the study on wind turbine wakes ispresented using the generalized actuator disk method and actuator line method in this paper.The generalized actuator disk method combines the actuator disk theory with common CFD,using the actuator disk model to represent the wind rotor, and focus on the wind turbine wakes withCFD, unnecessary to resolve blade boundary layers compared to a pure CFD approach. Thegeneralized actuator disk method is implemented in two ways in this paper:(1)The pressure reductionof the stream flowing through the wind rotor is considered with the pressure jump method to reflectthe effect of wind rotor extracting energy from the air. The velocity distribution in the far wakeobtained by this method is in good agreement with the experimental measurements.(2) With theaerodynamic model of the blade element momentum (BEM) theory, the aerodynamic loadsdetermined by the inflow conditons and aerofoil coefficients are used to replace the role of the bladesin the flow field as a momentum source. The NREL Phase VI wind turbine is chosen for calculation toverify the accuarcy of the aerodynamic loads obtained by the method, and the method is thenpeformed for two NH1500wind tubines in tandem to investigate the interaction effects of the wakecreated by the front wind turbine on the downstream wind turbine performance in various distancesbetween the two wind turbines.Based on the generalized actuator disk method combining with BEM, the actuator line methoddiscards the hypothesis of actuator disk. Instead, the aerodynamic loads are distributed along theradial lines representing the forces on the blade as a momentum source. Contrasting to thehomogenization on the near wake in the generalized actuator disk method, the actuator line methodcan simulate the induction due to the near wake, and can get distinct blade-tip vortex structure. Theflow field of the near wake modeled by the actuator line method is compared with that modeled bycommon CFD in detail, showing that the actuator line method is reliable.