Performance evaluation of a short-tube ducted tidal stream turbine: A hybrid framework integrating lattice Boltzmann simulation and orthogonal experimental design

Deep-sea weak-current conditions lead to severe performance degradation of horizontal-axis tidal stream turbines (TSTs), posing a major barrier to reliable tidal energy utilization. This study proposes a short ducted TST for low-flow-velocity environments and establishes an integrated framework combining water-flume experiments, lattice Boltzmann method-large eddy simulation method, and orthogonal experimental design. The key geometric parameters governing duct-induced acceleration were identified, revealing their influence hierarchy with strong statistical robustness. A coupled “external resistance–internal suction” mechanism was found to drive flow acceleration, enabling the optimized duct to increase the flow velocity. The ducted TST significantly increased the power coefficient relative to the open TST. The increment varied by inflow velocity, reaching 50%–130% under medium-to-high velocities and being more pronounced under low velocities, while also eliminating the near-zero-efficiency bottleneck in very low-flow-velocity condition. Flow-field analysis showed that, compared with the open TST, the ducted TST had a higher overall velocity ratio, a noticeably expanded wake width, and an obviously meandering wake. Additionally, its tip vortices merged earlier accompanied by more prominent large-scale vortical structures in the wake. The ducted TST maintained a stable wake recovery length and exhibited higher turbulent kinetic energy dissipation rate at the recovery position. Moreover, the ducted TST achieved significantly higher energy capture efficiency per unit length. The proposed design offers practical guidance for enhancing tidal energy capture efficiency in deep-sea weak-current environments and supports the broader engineering application of marine renewable energy systems.