Experimental investigation of the asymmetric oscillation mechanism of an oscillating water column wave energy converter

• PIV reveals asymmetric oscillation of the water column within OWC converters, which may influence energy extraction efficiency. • Vortex generation and evolution exhibit distinct asymmetry between inflow and outflow phases, with complex vortex-flow interactions shaping the overall flow pattern and energy dissipation within the OWC. • Vortex intensity and its impact on flow dynamics exhibit a positive correlation with wave height, resulting in stronger vortices and more pronounced flow asymmetry under higher wave conditions. While numerous studies focus on the energy extraction rate of oscillating water column (OWC) converters, many assume symmetric water column oscillations within the flow field, despite observed discrepancies in real-world conditions. This study employs particle image velocimetry (PIV) to analyze flow field asymmetry under various regular wave conditions, with wave height being a key variable. Experimental results reveal significant differences in velocity distributions and flow patterns. At higher wave heights, a high-velocity region near the front wall of the OWC converter emerges as the primary outflow pathway, while the inflow largely adheres to the wave-induced flow velocity. These flow pattern variations closely correlate with the vortex evolution region. Further analysis uncovers asymmetry in vortex generation: the seaward vortex originates from a stable shear layer, whereas the leeward vortex forms through multiple flow separations and turbulent mixing. These vortices shape the asymmetric flow pattern, with the leeward vortex driving outflow near the front wall and the seaward vortex creating a high-velocity “curtain” that impedes water inflow. The inherent asymmetry in the flow field, minimal under weaker hydrodynamic conditions, becomes more pronounced at higher wave heights due to intensified vortex influences. Additionally, a symbiotic interaction between the seaward and leeward vortices is observed, where each influences the other's formation,This interplay ultimately impacts the overall flow dynamics and energy extraction efficiency.