Numerical Study of a Wells Turbine with Variable Pitch Rotor Blades

The Wells turbine is a self-rectifying axial turbine widely used in wave energy conversion systems based on the Oscillating Water Column (OWC) principle. In these systems, the periodic movement of the water surface inside a chamber open to the sea determines an alternating flow of air inside a duct, where a Wells turbine can be used to convert flow energy into mechanical energy. The architectural simplicity and the reliability of the Wells turbine represent its strengths, while the limited operating range due to the aerodynamic stall of the blades at high flow rates is probably its greatest drawback, as it limits the performance of the entire system. In this paper, a computational investigation on the aerodynamic performance of a variable-pitch Wells turbine is presented. Fluid dynamics simulations were conducted using commercial CFD software and focused on defining machine performance at different flow rates and blade pitch angles. Numerical results obtained have been exploited to define a pitching law, applicable for a period of operation of the OWC system, which allows to adapt the blade's setting angle to the variable relative flow, thus obtaining an extension of the machine's operating range, and maximizing energy production.