ON THE WAVE-U-OWC INTERACTION IN A NUMERICAL 2D WAVE FLUME

Several wave energy conversion techniques have been patented all over the world. Despite this large variation in design, the Wave Energy Converters (WECs) are generally categorized by location, type and modes of operation. An Oscillating Water Column consists of a chamber with an opening to the sea below the water line. An OWC consists of a box with a big vertical opening in the front wall. Waves enter through this opening with only some small diffraction effects from the front wall (and they propagate on the water surface in the box. On the roof of the box there is a tube connecting the atmosphere with the air pocket enclosed between the water surface and the roof. This tube contains one or more self-rectifying turbine (like the Wells). The air pocket inside the box, is compressed and expanded alternately. As a consequence, an air flow is produced which drives the turbine in the tube. In the conventional OWC waves enter the plant undergoing some diffraction effects produced by the lower end of the front wall. U-OWC plants are breakwaters in reinforced concrete embodying an OWC with an additional vertical duct on the front wall. In this work, we carried out a numerical experiment aiming to analyze the interaction between waves and a U-OWC breakwater. The numerical method adopted is the numerical integration of Reynolds averaged Navier-Stokes equation (RANS). The water-air interaction is taken into account by means of the Volume Of Fluid (VOF) model implemented in the commercial CFD code Ansys Fluent. To validate the numerical flume, we carried out some preliminary tests finalized to compare numerical results of a vertical reflecting wall with the analytical solution of linear standing waves. The results have shown that there is a suitable correspondence between analytical and numerical simulation and this confirms that the wave field expanding along the wave flume has the characteristics of a progressive wave. The progressive wave train propagating in the wave flume impacts on a vertical wall and is reflected backwards. The reflected wave train superimposed with the incident waves generates a standing wave field propagating from the breakwater towards the wavemaker. The numerical experiment has been carried out by substituting the vertical wall with the U-OWC. The geometry and size of the U-OWC breakwater utilized in this work is the same as the 1:6 scale physical model of breakwater tested directly, at sea, off the coast of Reggio Calabria (in the eastern coast of the Messina Straits). The performance of the plant depends on whether it is working in resonance or not. To check the plant working conditions, we choose waves with characteristics (height and period) similar to those which interacted with the plant at sea. Therefore, we made several simulations, varying the wave period in the range [2.5, s 9 s] and maintaining the wave height fixed at 0.2m.