Mapping the wake of a full-scale floating tidal turbine platform

Significant effort has been devoted to the study of marine turbine wakes using numerical models and laboratory experiments. Recent deployments of full-scale hydrokinetic turbines in rivers and tidal channels provide new opportunities to map these wakes in the field, contributing to the development and validation of such models. However, efficient field methods that can accurately map the spatial structure of these unsteady turbulent flows need to be applied to quantify the wakes’ extent and evolution.

In this investigation, mobile platforms are used to map the flow downstream of Sustainable Marine Energy PLAT-I floating tidal energy platform. PLAT-I, supporting four 6.3 m horizontal-axis Schottel turbines, was deployed in Grand Passage, one of Bay of Fundy’s tidal channels in Nova Scotia, Canada, on September 2018. Stream-following surface drifters, equipped with turbulence-resolving Acoustic Doppler current profilers (ADCPs) and GPS trackers, were released just downstream of the turbines hundreds of times at different stages of the tide, covering the extent of PLAT-I’s wake. Collected data are used to estimate mean flow and turbulence parameters as a function of position both within and outside the wake. Along-drift data successfully capture the wake, showing slower velocities around hub-depth, vertical velocities of increased magnitude, and increased turbulent kinetic energy dissipation rates near the turbines. Both turbulent kinetic energy and dissipation are spatially coherent and distribute log-normal as previously observed in Grand Passage. Data are organized in time and space to construct synoptic maps of the platform wake for different flow conditions. The turbine’s combined wake shows a deficit in along-channel velocities extending about 200 m downstream of the platform and increased turbulent kinetic energy within the wake.