The flow field in the near wake region of a tidal current turbine is strongly driven by the combined wake of the device support structure and the rotor. Accurate characterisation of this region of flow is important but it is characterised by highly turbulent, slow-moving fluid.
Wake flow field characteristics of a 1:20th-scale horizontal axis turbine has been have been measured in a large water channel facility. A downstream map of both the channel base flow and downstream wake was made using both laser and acoustic doppler velocimeters. Wake mapping was conducted with the rotor in both operational an inactive states to quantify the effect of the turbine support structure upon the near wake flow properties.
Results indicate that the wake created by the turbine support structure has a significant effect upon the near wake flow field with strong synergistic effects of both rotor and supporting structure close to the downstream centre plane of the rotor which diminish with increasing lateral (cross channel) distance. Determination of higher order flow properties was difficult close behind the turbine (<4 rotor diameters) due to extremely high levels of turbulence. Furthermore, it is clear that the form of the rotor support structure has a strong influence upon near wake properties and this will change for the various forms of tidal energy devices either deployed or at the design stage.