Mitigating Uncertainty in Tidal Turbine Performance Characteristics from Experimental Testing

The paper presents data from two experimental campaigns at CNR-INSEAN’s towing tank in Italy and Strangford Lough tidal test site in Northern Ireland. The experiments maintained identical instrumentation between the campaigns allowing the comparison of steady uniform flow with unsteady non-uniform conditions, respectively. The three blade rotor is designed by Schottel Hydro Ltd for the SIT250 device, scaled to 1.5m diameter. The flow instrumentation used in this paper are Nortek’s Aquadopp 2 MHz Acoustic Doppler Current Profiler (ADCP).
The comparison between controlled laboratory and uncontrolled tidal environment is made by adopting a methodology for assessing turbine power performance using ADCP inflow data. The method allows the inflow velocity to be equated to a single measurement, using the power and area-weighted velocities across the swept area of the turbine’s rotor. The method has been expanded to include uncertainties and significant factors contributing to uncertainty have been identified. The carriage velocity was used to calibrate the inflow measurements in the laboratory environment, providing confidence intervals for performance. The Schottel SIT250 scaled blades had a peak hydrodynamic performance of CP=0.44 and 0.38 at CNR-INSEAN and Strangford Lough respectively. The difference between the performance in the towing tank and at the tidal test site are discussed with attributed causes presented as a result of Doppler noise biasing and the non-uniform, turbulent inflow velocity at Strangford Lough.