Revisiting Wells Turbine Hysteresis in Light of Existing Literature on Moving Airfoils
A Wells turbine is an axial-flow turbine consisting of a rotor usually with symmetric (uncambered) blades staggered at a 90 degree angle relative to the incoming flow. This turbine is used within oscillating water column (OWC) systems, which convert the sea-wave motion into a bi-directional flow of air. During its normal operation, the turbine blades experience a continuous change in incidence angle. that according to many authors is at the origin of an hysteresis in its force coefficients. Aerodynamic hysteresis in rapidly moving airfoils is a well-known phenomenon, but happens only at non-dimensional frequencies significantly larger than the ones encountered in Wells turbine. This work presents a re-examination of the two phenomena, that shows the unlikeliness of the presence of any aerodynamic hysteresis in Wells turbines. A simple and efficient lumped parameter analysis is used to prove how the real cause of the hysteresis is likely to be found in a completely different phenomenon, overlooked by many previous experimental and numerical analyses.