Characterization of a turbine wake in a tidal regime

A methodology to characterize a turbine wake under realistic tidal conditions, considering the temporal variability of both velocity and turbulence, is presented. It consists of a sequence starting with ADCP measurements at the potential zone, following with a hydrodynamic model of the zone, and ending with CFD modelling. A river estuary with one of the many high energy potential sites in the Southern Patagonian coast of Argentina, is selected for illustration. ADCP measurements are performed to determine velocity and turbulence profiles at different stages of the tidal cycle and at different locations within the area of interest. These data are used to calibrate the hydrodynamic model of the estuary, from which points of interest for turbine deployment are selected. The hydrodynamic model provides boundary conditions for CFD simulations. The analysis is performed for a floating turbine at two locations with similar velocities but different turbulence characteristics, and for a bottom mounted turbine at one of those locations. It is shown that the usual methodology of considering standard incident conditions falls short in delimiting the impact zone of the turbine. The concept of Permanence Limits for wake length and maximum width is introduced, as simple indicators to synthesize the effects of unsteadiness due to the tide, allowing the practitioner engineer to establish the span of time with values below the required limit, once a threshold for the velocity recovery is adopted.