Rapid advancements in renewable energy technologies have been primarily driven by the increasing global energy demand for energy and the growing concerns over environmental pollution. Among these technologies, tidal current energy has achieved significant attention due to its high energy density and stable energy output. Compared to other renewable energy sources, such as solar and wind power, tidal current energy is more stable and predictable, offering considerable potential for integration into future energy systems. However, despite its promise, several key technological challenges must be addressed to enable the widespread development of tidal current energy technology. To address these challenges, this paper presents a comprehensive review of recent advancements in ocean tidal current energy technology, with particular emphasis on the analysis of the main types of energy harvesting devices and support structures. Furthermore, it evaluates representative tidal current energy devices based on their operational principles, technical features, and applications. By systematically reviewing mainstream hydrodynamic analysis methods, this paper evaluates their applicability and limitations in assessing the performance of tidal current energy devices. This assessment improves the accuracy of performance predictions and offers theoretical support for the optimal design of the energy harvesting systems. In addition, the paper addresses key issues in the development of tidal current energy technology, including technological feasibility, cost management, and environmental impact. These discussions provide a foundation for identifying emerging trends and major technical challenges in the field. Finally, the development prospects of tidal current energy technology are explored from the perspectives of technological advancement, economic viability, and sustainability. It is concluded that achieving widespread adoption of tidal current energy depends on factors such as technological maturity, effective cost control, and the balanced integration of environmental and social benefits.

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.

The misalignment between flow and rotor can significantly alter the efficiency of the tidal stream turbine (TST), and therefore, it is vital to predict the flow in the tidal field and the performance of the TST under yaw-offset conditions. First, this paper implements a high-precision Lagrangian dynamic sub-grid-scale model based on the large-eddy simulation (LES) method. A classical computational fluid dynamics benchmark case is selected to validate the accuracy of the dynamic LES (DLES) method. The results indicate that the newly implemented dynamic LES method exhibits reduced dissipation and effectively captures the local effects of non-uniform flow fields, including vortex structures. Second, an efficient high-fidelity numerical method (AL-DLES) for forecasting the TST wake is presented by integrating an actuator line (AL) code with the aforementioned DLES method based on the Lagrangian framework. After comparing the experimental results, it was discovered that the newly developed AL-DLES coupling approach, which addresses the issues of challenging turbine meshing, rapid wake dissipation, and insufficient flow field fidelity in previous methods, can accurately simulate the forces acting on the TST while also capturing detailed characteristics of the flow field. Furthermore, the study will be extended to investigate the TST wake dynamics under various yaw-offset conditions, exploring the mechanisms of instability evolution in wake meandering. Meanwhile, the latest third-generation (Ωnew) vortex identification program is implemented and successfully applied to the wake vortex visualization of the TST under yaw-offset conditions. Through a comparative analysis of three distinct vortex identification approaches, it was demonstrated that the Ωnew method exhibits superior accuracy in capturing the vortex system located behind the rotor, eliminating the need for manual threshold selection. In addition, it is capable of simultaneously capturing both strong and weak vortices, which is a vital aspect for future wake research.

This study investigates the impact of sidewall blockage effect on the hydrodynamic performance of twin-rotor vertical axis tidal stream turbine (TR-VATST) with varying solidities. A hydrodynamic analysis model for TR-VATST under sidewall blockage effect is developed using computational fluid dynamics. The hydrodynamic characteristics of TR-VATST in an unsteady flow field are numerically simulated, focusing on the influence of sidewall blockage effect on the energy extraction efficiency across different tip speed ratios and solidities. Base on these analysis, a modified model for sidewall blockage effect applicable to TR-VATST is proposed. The results indicate that: (1) the mean power coefficient of TR-VATST increases with the blockage ratio across different solidities, and the improvement is faster at higher solidity; (2) as the blockage ratio increases, the influence of sidewall blockage effect on TR-VATST intensifies, leading to an increase in the flow velocity near the blades, thereby enhancing energy from the incoming flow and improving the mean power coefficient; (3) The modified model for sidewall blockage effect accurately predict the mean power coefficient of TR-VATST within a specific range of tip speed ratios, solidities, and blockage ratios. Moreover, the model effectively eliminates the influence of laboratory flume sidewalls, enabling correction of experimental results to reflect offshore prototype performance in an unbounded flow environment. These findings provide valuable engineering insights for the performance prediction and optimization of TR-VATST systems.

In extreme marine environments, the interaction between offshore wind turbine pile foundations (OWTPFs) is critical, and the associated hydrodynamic loads are complex. This study focused on fixed OWTPFs and used computational fluid dynamics (CFD) to numerically simulate the flow field around pile foundations under the combined action of focusing waves and current. The objective was to investigate the influence of different focusing wave and current parameters on the hydrodynamic properties of the pile foundations. The findings indicate the following: (1) When the wave and current directions are opposite, the maximum wave force on the pile foundations is greater than when they are aligned. (2) Large-amplitude focusing waves around pile foundations generate secondary loads, which are nonlinear and lead to a rapid increase in the wave force. These secondary loads are short-lived and particularly prominent near the front row of pile foundations. (3) The influence of the group pile effect diminishes under high-amplitude waves, where the wave component dominates the generation of the dimensionless wave force, and the impact of the current on this force decreases.

In the array design of the vertical axis wind turbines (VAWT), the wake effect of the upstream VAWT on the downstream VAWT needs to be considered. In order to simulate the velocity distribution of a VAWT wake rapidly, a new two-dimensional numerical method is proposed, which can make the array design easier and faster. In this new approach, the finite vortex method and vortex particle method are combined to simulate the generation and evolution of the vortex, respectively, the fast multipole method (FMM) is used to accelerate the calculation. Based on a characteristic of the VAWT wake, that is, the velocity distribution can be fitted into a power-law function, a new correction model is introduced to correct the three-dimensional effect of the VAWT wake. Finally, the simulation results can be approximated to the published experimental results in the first-order. As a new numerical method to simulate the complex VAWT wake, this paper proves the feasibility of the method and makes a preliminary validation. This method is not used to simulate the complex three-dimensional turbulent evolution but to simulate the velocity distribution quickly and relatively accurately, which meets the requirement for rapid simulation in the preliminary array design.