Characteristics of vortex evolution around a cylindrical oscillating water column device: An experimental study

The utilization of oscillating water column (OWC) converters with existing hydraulic/coastal structures has emerged as a crucial approach for the development of economically viable and environmentally sustainable green power generation devices. Integrating OWC converters into offshore wind turbine (OWT) monopiles is a promising solution in wind power industrialization. This paper presents an experimental investigation of the flow characteristics of an OWT-OWC system under regular wave conditions, focusing on the evolution of vortex structures. Particle image velocimetry (PIV) is employed to measure the flow field surrounding the OWC converter under different wave heights and wave period conditions. Based on the measured velocity field data, the evolution of vortices is examined using the Q-criterion. The results indicate that the wave period significantly affects the flow patterns. Specifically, an increase in wave period enhances the three-dimensional nature of the flow field. The vortices outside the OWC chamber are observed to connect and form a three-dimensional vortex ring, hindering efficient wave energy conversion. Conversely, the variation in wave height exhibits limited impact on the flow field evolution. However, as the wave height increases, the vortex strength and asymmetry experience a significant rise, making it difficult to form a stable three-dimensional vortex ring. Moreover, based on optimal geometric design considerations, it is recommended to increase the lateral angle and height of the sidewall openings to prevent vortex ring formation and minimize obstructions, while ensuring the structural safety of the OWT.