Experimental Investigation on a Speed Controlled Wells Turbine for Wave Energy Conversion

Abstract Ocean wave energy represents one of the most attractive renewable sources due to its high availability and predictability. Solutions based on the Oscillating Water Column (OWC) principle are one of the most promising for sea-wave energy conversion. The system is composed of two main units, an open chamber that converts the sea wave motion into an alternating airflow, and a turbine driven by this flow. The typical alternating airflow inside the OWC chamber requires a turbine with self-rectifying behavior. The Wells turbine is the simplest and most reliable turbine for this purpose in virtue of its rotor with symmetric blades staggered at 90 degrees relative to the axis of rotation. The non-stationary operating conditions of the Wells turbine strongly affect its performance when working away from its optimal efficiency point. By controlling the turbine rotational speed, the operating conditions can be kept closer to the maximum efficiency point. Recent works, based on dynamic simulations, have proposed control strategies for the turbine rotational speed, to avoid stall occurring under variable wave conditions. The present work investigates a rotational speed control in order to keep the operating conditions closer to the turbine’s maximum efficiency point. The analyses have been conducted in an experimental facility capable to simulate an OWC system with regular (sinusoidal) wave motion. Wells turbine performance has been evaluated for different control laws and it is compared to not-controlled turbine performance in order to evaluate the effectiveness of the control action.