Dynamic interaction between OWC system and Wells turbine: a comparison between CFD and lumped parameter model approaches

Systems composed of an oscillating water column and a self-rectifying turbine are among the most well-known devices for wave energy conversion. These systems have been largely studied experimentally and numerically, focusing either on OWC hydrodynamic or power-unit performance. The turbine has been studied in experimental facilities that reproduced the periodic motion of the water column in the chamber by an artificially moved piston, while OWC performance has been generally studied neglecting or crudely simplifying the turbine interaction. The objective of this work is to introduce a lumped parameter model, able to reproduce the interaction of the turbine with the air mass in the OWC chamber. Results are compared with experimental and CFD data, and demonstrate that the often discussed hysteresis is caused by compressibility effects in the air chamber and not, as previously assumed, by turbine aerodynamics. The model is also used to estimate energy loss and phase delay in full-scale OWC systems, proving the importance of a correct sizing of OWC-turbine systems. The lumped parameter model allows to rapidly isolate parameters with the largest influence on system performance, and could be integrated with existing wave-to-wire models to improve the understanding of the hydrodynamic/aerodynamic interaction in the overall system.