Evaluation of an actuator-line model in a lattice Boltzmann solver for wake interaction between two in-line wind turbines

An in-house computational fluid dynamics (CFD) code based on the lattice Boltzmann method has been used to investigate the wake interactions between multiple wind turbines. This study assesses the accuracy of the numerical method by conducting a comparison computation on the Blind Test 2 (BT2) experiment, which aims to evaluate turbine performance and wake characteristics, such as mean velocity and turbulence intensity, for two turbines aligned in tandem and operating at different rotational speeds. In the present simulation, a hybrid approach is proposed for modeling the wind turbines, in which the blades are modeled using the actuator line method, and the nacelle and other structures are treated as solid bodies with the wall boundary condition implemented through an interpolated bounce-back scheme. The numerical results are validated against BT2 data and three earlier CFD studies. A mesh convergence test at four different resolutions shows excellent performance in predicting velocity deficits; moreover, the method effectively reproduces turbulence intensity profiles. Compared to previous CFD approaches, this hybrid method achieves superior accuracy, especially in regions where the nacelle and tower have a significant impact. Visualization of the three-dimensional flow field reveals that wake structures become highly asymmetrical due to the influence of the tower, and blade-tip vortices from the downstream turbine are breaking up in the high tip speed ratio region. Finally, the turbulence characteristics are analyzed based on three velocity fluctuation components, showing that the turbulence behind the nacelle and tower is isotropic. In contrast, the turbulence behind the rotor tips is highly anisotropic.