Experimental Results in a Variable-Pitch Wells Rotor

Systems based on the oscillating water column (OWC) principle are often equipped with Wells turbines as power take-offs (PTOs) to convert sea-wave energy. The self-rectifying nature of the Wells turbine represents a strength for such applications, while its limited operating range, due to stall, is one of the most relevant limitations. A possible improvement lies in varying the blade stagger angle during operation as this can delay stall by reducing the incidence angle. Although the performance of variable-pitch Wells turbines has been studied in the past, their local aerodynamic performance has never been investigated before. This study addresses this important task by experimentally reconstructing the flow field along the blade height of a Wells turbine prototype, coupled to an OWC simulator, for three values of the stagger angle. The aerodynamic behavior of the Wells rotor is characterized at its inlet and outlet, showing how the interaction between adjacent blades changes due to the stagger angle. The rotor performance is evaluated and compared, providing useful information that is of general validity for similar rows of symmetric blade profiles when pitched at different stagger angles.