Influence of incoming wave conditions on the hysteretic behavior of an oscillating water column system for wave energy conversion

Abstract

The performance difference of a Wells turbine in an oscillating water column (OWC) system in the acceleration and deceleration phases of the incoming waves is known as its hysteresis characteristic. In the present work, a laboratory OWC system is simulated numerically with deformable grids to simulate the air–water interface, and a lumped-parameter model is used to reproduce the interaction between the air flow and the Wells turbine in the OWC system. The model results are compared with experimental and numerical results, with excellent agreement, then the model is used to quantify the hysteresis intensity of the hysteresis loop under different incoming wave conditions and turbine rotation speeds. After separating the hysteresis of the OWC system from that of its Wells turbine, the lumped-parameter model shows that the former is due largely to the compressibility of the air in the chamber. When the compression ratio of the OWC system decreases from 4.40 to 2.00, the hysteresis intensity of the hysteresis loop decreases by 64.13%, and when the rotation speed of the Wells turbine increases from 3600 rpm to 4800 rpm, the hysteresis intensity increases by 34.53%. The present work contributes to predicting the performance of Wells turbines and quantifying the hysteresis intensity for maximum extraction of sea-wave energy.