Analytical Models of Oscillating Water Column Systems Operating with Air Turbines in the Mediterranean Sea

One of the global challenges of the millennium is bringing renewable energy conversion systems to an industrial maturity. Sea is an important resource in terms of extension and energy potentially exploitable by waves, currents, tides and thermal gradients. Amongst these physical phenomena, sea waves are the source with the highest energy density. A suitable solution for an effective conversion of this source is represented by the oscillating water column (OWC) systems, operating either with Wells or impulse turbines. In these systems, the primary converter, represented by the chamber structure, transforms the sea wave motion into an oscillating air flow that is forced to pass through the secondary converted, represented by the air turbine. Analytical models of the primary and secondary converter were created. A rigid piston model was realised to solve the hydrodynamics and thermodynamics of the chamber, coupled with the turbine. The aerodynamics of Wells and impulse turbines were solved by considering the turbomachine cascades as sets of blades, comprised of a finite number of aerofoils stacked in the radial direction. The analytical models were applied to the evaluation of the performance parameters of OWC systems operating with these turbines in environmental conditions typical of the Mediterranean Sea. Finally, two configurations of the OWC system capable to convert an equivalent annual energy of about 163 MWh were compared.