Research on the Power Capture and Wake Characteristics of a Wind Turbine Based on a Modified Actuator Line Model

On a wind farm, the wake has an important impact on the performance of the wind turbines. For example, the wake of an upstream wind turbine affects the blade load and output power of the downstream wind turbine. In this paper, a modified actuator line model with blade tips, root loss, and an airfoil three-dimensional delayed stall was revised. This full-scale modified actuator line model with blades, nacelles, and towers, was combined with a Large Eddy Simulation, and then applied and validated based on an analysis of wind turbine wakes in wind farms. The modified actuator line model was verified using an experimental wind turbine. Subsequently, numerical simulations were conducted on two NREL 5 MW wind turbines with different staggered spacing to study the effect of the staggered spacing on the characteristics of wind turbines. The results show that the output power of the upstream turbine stabilized at 5.9 MW, and the output power of the downstream turbine increased. When the staggered spacing is R and 1.5R, both the power and thrust of the downstream turbine are severely reduced. However, the length of the peaks was significantly longer, which resulted in a long-term unstable power output. As the staggered spacing increased, the velocity in the central near wake of the downstream turbine also increased, and the recovery speed at the threshold of the wake slowed down. The modified actuator line model described herein can be used for the numerical simulation of wakes in wind farms.

Development of an Actuator Line Model for Simulation of Floating Offshore Wind Turbines

This study focuses on developing and applying an actuator line model (ALM) to predict the wake behind floating offshore wind turbines (FOWTs). A computational method is presented which implements an ALM, able to handle 6 Degree-of-Freedom (DOF) motion dynamics, coupled with a CFD solver. Computational grides used are cubic and do not require a boundary layer mesh. Results show that just about 300k grids are necessary for performance assessment of the NREL Phase VI case. Therefore, the proposed method leads to significantly lower computational cost and easier preprocessing compared to high-order methods used for solving RANS. On the other hand, coupled aerodynamic and motion analyses showed that pitch and surge motions have the most considerable influence on turbine performance due to their inherent effect on 3D local wind inclination in the relative frame. The peak power happened when the platform is in its initial position, where the platform motion velocity is maximum. Finally, it is shown that the wind turbine movement has a considerable effect on its wake characteristics. The gap distances between wake rings can also change wake interactions, and, for the case with platform pitch motion, the condition of the wake is even more complicated as such distance is not the same in all azimuthal sectors. The results show that the applied ALM method is beneficial for simulating the wake behind offshore wind turbines and the complex phenomena in the wake due to platform oscillation.