Experimental and numerical investigations of Wells turbines for wave energy conversion

This thesis deals with the evaluation of the performance of a Wells turbine both with experimental and numerical investigations. In particular, results are used to highlight the contribution of different loss sources in determining the turbine efficiency. Numerical investigations have been focused at calculating the turbine efficiency using both direct and indirect methods, i.e. by considering the quantities of interest at the inlet and at the outlet of the turbine, as well as through the estimation of entropy generation inside the domain. Experimental investigations have been conducted at the University of Cagliari in a facility equipped with an Oscillating Water Column (OWC) simulator and a Wells turbine. The facility has been modified following a modular design of the test section, which allows an easier modification of the rotor configuration and simpler access to the test section for local flow investigations. Investigations have been focused on the determination of Wells turbine performance, both with global measurements (such as torque and static pressure drop) and detailed local measurements. Local investigations were carried out using aerodynamic probes and hot-wire anemometer (HWA), in order to reconstruct the flow field near the turbine, hence to estimate also the local performance and losses. The analysis of turbine’ s performance suggests two possible solutions to improve Wells turbine performance under periodic unsteady flow conditions, characteristic of the OWC device. The first solution is based on controlling the rotational speed of the rotor, while the second one requires a modification of the pitch of the rotor blade to control the incidence angle at different flow rates. The former solution has been experimentally investigated in the facility available at the University of Cagliari, while the latter has been evaluated by means of two dimensional CFD simulations.