Wells turbine used for wave and wind power generation is known to generate loud noise during its operation. Aerodynamic noise reduction is an important issue in the design of the turbines. Since aerodynamic noise depends highly on behavior of the vortices around the turbine and the wake region, understanding of the unsteady flow past a rotating turbine plays important role. In this study, we modeled the Wells turbine and serrated turbine, and visualized flow separation and vortex generation past the rotating turbine by using numerical simulation with LES turbulent model. In order to evaluate the turbine performance, axial torque was numerically evaluated. In addition, this study compared numerical results obtained by the moving mesh method and the method of rotating coordinate system.