A novel actuator line-immersed boundary (AL-IB) hybrid approach for wake characteristics prediction of a horizontal-axis wind turbine

The core idea of the actuator line (AL) model is to simplify the horizontal-axis wind turbine (HAWT) into a line with force distributed along the radial direction. The body force on the AL is employed to simulate the effect of the HAWT on the flow field, and the Navier-Stokes (N-S) equation is solved to obtain the aerodynamic and wake characteristics of the HAWT. Recently, the AL model has been comprehensively implemented in the investigation of wind turbine wakes. However, the existing standard AL model ignores or inaccurately describes the nacelle effects, which have been proven to considerably affect the accuracy of the near wake simulation. This paper develops an actuator line-immersed boundary (AL-IB) hybrid approach for the HAWT with high-accuracy and low-computational cost to address the physics problem underlying here. The wind turbine adopts the AL model instead of the body-fitted mesh method, and the nacelle is realized by the immersed boundary (IB) method. The large eddy simulation (LES) with a new localized dynamic Smagorinsky (LDS) sub-grid scale (SGS) model is adopted to model the turbulence to improve simulation accuracy of the near wake, thereby forming a set of high-fidelity numerical simulation framework of the HAWT wake. Firstly, the simulation accuracy of the AL-IB hybrid approach is validated by comparing the mean wake velocity profiles and turbulent kinetic energy (TKE) profiles of the HAWT with the experimental measurement results of the NTNU "Blind test 1". Furthermore, the research is extended to the wake difference of the HAWT under two different numerical methods (AL and AL-IB). The results show that the solver developed based on AL-IB hybrid approach has higher accuracy than the standard AL model, which provides a feasible way for the refined numerical simulation of the large-scale wind farm.