Performance and wake characteristics of a tidal turbine operating at different tip speed ratios in elevated free-stream turbulence
Cong Han, Arindam Banerjee
Abstract
Tidal turbines operate in open-water environments that have an elevated level of free-stream turbulence, leading to dynamic inflow conditions that do not coincide with a rated or design operating condition. A detailed experimental campaign was thus conducted using a 1:20 scale turbine that was subjected to varying levels of elevated turbulence for three pre-selected tip speed ratios that mimic different operating scenarios; a comparatively low TSR (<3), an optimum TSR (4.5–5.0), and a large TSR (>6). Turbine performance and near-wake characteristics (including recovery) were measured and compared with the turbine operating in a quasi-laminar inflow, i.e., without background inflow turbulence. The experimental results reveal that TSR has a significant effect on the wake. Increasing TSR results in more significant wake deficits, more intensive momentum exchange in the near-wake region, and faster wake recovery due to strong wake mixing with the bypass flow. Early breakdown of tip vortices in the wake were also observed at the largest tested TSR.