Real-time Wells turbine simulation on an oscillating-water-column wave energy converter physical model

Due to its simplicity and low cost, the Wells turbine is the most common choice for driving oscillating-water- column (OWC) wave energy converters (WECs) power take-off system. This turbine is characterized by a flow rate that is a linear function of the pressure head and inversely proportional to the rotational speed before the onset of hard stall conditions. The Wells turbine has been simulated in wave tanks using porous plugs, where the flow rate exhibits linear behaviour. However, numerical and experimental results have shown that rotational speed variations significantly influence the performance of OWC WECs. This work aims to develop a novel real-time simulator of a Wells turbine for use in physical models of OWC power plants. The proposed simulator consists of a diaphragm whose diameter is adjusted in real-time as a function of the pressure head measured in the laboratory and the rotational speed calculated by a hardware-in-the-loop model. In this way, it is possible to reproduce the full behaviour of the Wells turbine before and after a hard stall. Experimental results demonstrate the effectiveness of the simulator. A performance analysis was conducted to understand the device's potential and compare the damping that Wells and impulse turbines introduce.