The actuator line method (ALM) introduces an actuator-line to represent a wind turbine by adding a body force term in the momentum equation. As ALM simplifies the process of mesh refinement and moving mesh, it can get much higher efficiency for wind turbine wake simulation. In this paper, ALM is implemented to investigate the NREL 5-MW wind turbine wakes by using OpenFOAM. The results of the power and the thrust of NREL 5-MW wind turbine can get a good agreement with the results of benchmarkes. According to the analysis of wind turbine wakes in details, ALM can predict wind turbine wakes accurately.
The effect of wind turbine wakes always makes the whole wind farm production turning decline (Gaumond et al, 2013). Generally speaking, it is significant for the wind farm control strategies, but the wind turbine wakes are so complicated and difficult to simulate. At present, the Blade-Element\ Momentum (BEM) theory (Betz, 1920; Glauert, 1935) and computational fluid dynamics (CFD) method are frequently adopted to the load simulations (Tran et al, 2012) and performance calculations (Sanderse et al, 2011) of wind turbines. The BEM model is simple and fast, but it needs to introduce some corrections to get higher accurate results, such as dynamic stall, tip loss, added mass of rotors, et al. However, CFD method is very expansive for CPU time and can get highly accuracate results without these corrections. Even so, many researches concentrated on wind turbine wake simulation with CFD (Liu YC et al, 2017).
Then, ALM was introduced by Shen and Sørensen (2002). It adds a body force term in a three dimensional Navier-Stokes solver, body forces are distributed radially along the blades. The body force is the load on the blade calculated by tabulated airfoil data and local angles of attack. With this concept, the dynamics of the wake and the tip vortices can be studied fastly and completely. Troldborg (2008) pointed out that ALM can be used to reproduce the vortex accurately and only use simple structured grids. In addition, it is effective to calculate the loading on the blade (Shen et al, 2012). However, most models by using ALM do not consider elastic blades and the motion of each element is rigid body rotation. Hang Meng et al (2018) combined the ALM and a finite difference structural model, and named it as elastic actuator line (EAL). Nevertheless, that is the first step to propose the concept of EAL and it still exists some limitations which need to do further study.
