A Virtual Instrument Approach for Improved Tidal Turbine Wake Measurement

Accurate measurements of the wakes generated by the operation of tidal energy converters are required for the calibration and validation of tidal turbine wake models embedded in tidal site models. These site models are a key tool in designing tidal arrays. Wakes are inherently difficult to measure using Acoustic Doppler Current Profilers (ADCPs) due to these instruments reliance on assumptions of flow homogeneity in the profiled horizontal planes. This work presents a Virtual ADCP (VADCP) instrument which can be deployed within hydrodynamic site models to provide idealised estimates of instrument performance degradation. These performance maps can be used to identify optimal deployment locations and orientations for instruments for improved wake measurement campaigns. Results show that VADCPs deployed within the path of the wake with a suboptimal heading alignment experienced mean errors of up to 25% of the intensity of the wake. Modeling indicated that aligning two of the VADCPs acoustic beams with the flow direction of the wake minimized errors and saw limited performance degradation between instruments in the free flow and those deployed in the wake path. VADCPs deployed with heading alignments at 45° to the path of the wake showed increases in wake measurement RMSE of 19% of compared to the VADCPs deployed at 0°.