Underwater LED-based Lagrangian Particle Tracking Velocimetry

A new white-light volumetric flow measurement technique is presented that can be used in large-scale facilities. The technique enables large volumes to be measured with high temporal and spatial resolution and without the need for a class-4 laser. This LED-based Lagrangian particle tracking velocimetry is demonstrated by measuring the tip vortex formation and the near wake of a 1.2~m diameter tidal turbine in a 25~m diameter, 2~m deep tank. Seven streamwise-distributed volumes of interest are combined, each 334~mm long, 244~mm wide and 140~mm deep, reaching up to one diameter downstream of the turbine. The system does not require re-calibration when moved. By assuming a periodic flow field, a phased-averaged flow field was reconstructed with a temporal resolution of 3.9 ms and a spatial resolution of 5.4 mm. The large volume and high time and spatial resolution could enable key research questions to be addressed on high-Reynolds-number flows and could provide valuable benchmark data for numerical model development and code validation.