Wells turbine is an axial flow air turbine extensively used in the oscillating water column (OWC) of ocean energy harvesting device. The turbine has low aerodynamic efficiency at higher flow rate and poor starting characteristics. In this paper, the characteristics of the hysteresis behavior of a Wells turbine for a wave energy conversion device under alternative axial flow conditions are reported. The numerical work is carried out by solving the three-dimensional unsteady Reynolds Average Navier–Stokes equations (URANS) with two-equation eddy viscosity model. It is noticed that the unsteady numerical results are associated with two hysteresis loop. In the clockwise hysteresis loop, larger flow separation can be noticed on the blade suction side due to stronger vortex while flow separation decreases due to weaker vortex during counterclockwise hysteresis loop. Also, the effect of the blade sweep and blade profile thickness on the hysteresis behavior of the wave energy conversion device are reported. © Springer Nature Singapore Pte Ltd. 2019.