Experimental investigation of the energy extraction by a fully-passive flapping-foil hydrokinetic turbine prototype

Experiments were conducted to assess the performance of a fully-passive flapping-foil hydrokinetic turbine for which the self-induced and self-sustained blade motions are resulting from the interaction between the blades elastic supports (springs and dampers) and the flow field. Previous numerical studies have shown that such a turbine can extract a substantial amount of energy from the flow while offering the possibility to simplify the complex mechanical apparatus generally needed to constrain and couple the blade pitching and heaving motions in the case of the conventional fully-constrained flapping-foil turbine. Based on these promising numerical investigations, a prototype was designed and tested in a water channel at a chord Reynolds number of 21000. Robust and periodic motions of large amplitudes were observed leading to an energy harvesting efficiency reaching 31% and a power coefficient of 0.86. The sensitivity of the turbine dynamics to seven different structural and inflow parameters was evaluated experimentally around a baseline case achieving a high level of performance. It was found that the turbine maintains a good performance over a large range of parameters. (C) 2018 Elsevier Ltd. All rights reserved