Hydrodynamic performance of single-chamber and dual-chamber offshore-stationary Oscillating Water Column devices using CFD

The Oscillating Water Column (OWC) is considered to be one of the most promising Wave Energy Converter (WEC) concepts in terms of practicality, survivability and efficiency. To date, most research has focussed on single–chamber devices, but it is suggested that significant increases in energy extraction can be achieved from dual–chamber devices. This paper investigates, using well–validated 2D and 3D CFD models based on the Reynolds Averaged Navier–Stokes (RANS) equations and the Volume of Fluid (VOF) method, the hydrodynamic performance of various dual–chamber offshore–stationary OWC–WECs and compares the results to single–chamber OWC devices. The effect of chamber lip draught, chamber length in wave propagation direction and the power take–off (PTO) damping on the capture width ratio (power extraction efficiency) of each OWC device was studied over a wide range of wave periods for a constant regular wave height. It was found that all the parameters tested were important for the design of efficient OWC devices, and the dual–chamber device provided superior results to the single–chamber device, especially over the intermediate and long wave periods where the capture width ratio could be improved by a maximum of about 140%; hence extracting significantly more energy. The effectiveness of using the dual–chamber system was more obvious when 3D effects were considered. The findings of this paper contribute towards the design and operation of practical OWC devices for efficiently utilizing ocean waves to produce electricity.