Abstract
Ducted turbines have the potential to generate large-scale electricity when placed in tidal farms. Understanding the fluid-duct interaction would provide vital information for tidal farm projects. This paper describes flume experiments to investigate the performance and far wake impact on flanged duct turbines in bi-directional tidal flows. Results showed that ducted turbines generate 40% more power per rotor unit area than bare turbines. The turbines underperformed for each device in tandem configurations. However, ducted turbines outperformed bare turbines by 15%. The decreasing range of wake velocities and increasing turbulence intensities of the devices were shown to be greater in the ducted turbines. The drop in wake velocity is caused by kinetic energy extraction, and duct and rotor blockage effects. For the isolated bare and ducted turbines, full flow recovery occurs at around 13 and 20 rotor diameters, respectively. In tandem arrangements, while the bare turbine operated as if it was in isolation from 24 rotor diameters downstream, the wake flow in the ducted turbines persisted beyond. However, in terms of power output per rotor unit area, the deployment of additional ducted turbines may be advantageous. Though in the present state of development, precise economic estimates of energy costs are unavailable.