Influence of the longitudinal spacing on a two-unit tandem tidal turbine arrangement in turbulent flow

The performance and interactions of turbines within tidal energy arrays are critical to optimizing power generation and minimizing environmental impact. This study experimentally investigates the performance and wake characteristics of a two-unit tandem tidal turbine arrangement under turbulent flow conditions, focusing on longitudinal spacings of 6D and 8D. Compared to a single turbine, the downstream turbine experiences significant power loss and operational limitations due to reduced inflow velocity and elevated turbulence intensity. These effects disrupt wake recovery and enhance energy exchange with the surrounding flow, particularly near the free surface. At optimal conditions, the power coefficient decreases from 0.343 for a single turbine to 0.189 and 0.234 for 6D and 8D longitudinal spacings, respectively. A validated superposition wake model demonstrates improved predictions in the far wake region, offering insights into array layout optimization. This work provides actionable guidance for designing efficient tidal turbine farms, with a specific emphasis on wake dynamics and inter-turbine spacing.