Design of a ducted wind turbine for offshore floating platforms

Abstract

Within the Marine Energy Laboratory project, funded by the Italian Ministry for Education, University and Research, one of the first offshore wind plants on floating hulls, hosting ducted wind turbines, has been considered. The confinement of horizontal-axis wind turbines inside divergent ducts is reconsidered, in light of material innovation and direct drive coupling. Ducted wind turbines can take advantage of the flow rate increase due to the effect of the divergent shrouds. The conventional blade element momentum theory has been reformulated in order to deal with ducted turbines. Furthermore, computational fluid dynamics simulations have been carried out based on the solution of the steady two-dimensional Reynolds-averaged Navier–Stokes equations for axisymmetric swirling flows. In order to avoid any expensive mesh refinement near the actual rotor blades, the turbine effect on the flow field is taken into account by means of source terms for the momentum equations solved inside the domain swept by the rotor. This technique allowed us to optimize the geometry of the ducted wind turbine in an extremely effective way.