Experimental investigation of vortex evolution around oscillating water column wave energy converter using particle image velocimetry

Although the oscillating water column (OWC) wave energy converter has been extensively studied in recent decades, the understanding of the flow field around the OWC converter is still in its infancy due to the complexity of the wave-structure interaction, especially with the vortex evolution. In this study, the characteristics of the flow field around the OWC converter were investigated by using the time-resolved particle image velocimetry technique to analyze the temporal development of the vortex in the vicinity of the OWC converter. The Q criterion was calculated to highlight the vortex intensity, and the entropy was used to analyze the energy dissipation. The results indicated a close relation between the energy dissipation and the formation of vortices. The temporal processes of vortex generation and development were elaborated in terms of phase-averaged results, including their variations with wave heights and wave periods. It was found that the vortex intensity and structure were clearly affected by the wave heights. As the wave period increased, the position of the seaward vortex shifted downward, while that of the leeward vortex shifted upward and deeper into the chamber. In addition, the detailed flow field results provided insight into the effect of vortex evolution on the energy extraction rate of OWC, showing that the leeward vortex led to a decrease in the energy extraction rate, while the seaward vortex led to more energy dissipation as the water leaving the OWC converter and had a relatively small effect on the energy extraction rate.