Lagrangian dynamic large-eddy simulation of the performance of a horizontal-axis tidal turbine with an actuator-line method

Abstract

In the context of global carbon peaking and carbon neutrality goals, the development of clean energy technologies has become a strategic priority for the global community. As a significant source of renewable energy, tidal current energy is playing an increasingly important role in reshaping the global energy landscape. To address the critical scientific challenge presented by the wake effects induced by tidal turbines, this study introduces a high-precision Lagrangian dynamic (LD) sub-grid-scale model within the framework of large-eddy simulation (LES). By integrating the actuator-line model with the aforementioned LD–LES approach, a solver named JUST–FOAM–Turbine is developed, specifically tailored for high-fidelity wake simulations of horizontal-axis tidal turbines (HATTs). The solver's computational accuracy is validated against experimental data obtained from laboratory-scale HATT tests. Subsequently, the solver is employed to analyze the wake dynamics of the HATT under various tip speed ratios (TSRs). The findings are summarized as follows: (1) At low TSRs, the blade operates at a high angle of attack, increasing its susceptibility to stall and flow separation. At high TSRs, the blade experiences a low angle of attack, resulting in a reduced lift coefficient. In contrast, within the optimal TSR range, which corresponds to the blade's primary operational regime, the angle of attack is maintained near the critical value, thereby maximizing the turbine's power output. (2) As the TSR increases, the wake instability of the turbine intensifies, and the wake meandering phenomenon becomes more pronounced. The wake expansion downstream of the turbine is primarily driven by the blockage effect. Further downstream, the wake continues to widen laterally, resulting in an increased expansion width. (3) At a downstream distance of 6D, the wake effect begins to weaken due to momentum exchange between the low-speed region of the wake and the high-speed region of the surrounding water. The radial velocity gradient of the wake decreases significantly. When considering the turbine array layout, it is recommended to position additional turbines downstream beyond 6D. (4) As the TSR increases, the attached vortex on the turbine disk progressively disintegrates, forming small-scale, weaker vortex structures. The third-generation vortex identification method implemented in this study is threshold-independent and effectively captures both strong and weak vortex structures in the turbine wake simultaneously.

Topics & Concepts