Twisted Darrieus turbine was suggested as an amelioration of conventional Darrieus rotor by modifying it to have helical blades. This reform affords the twisted turbine better performances with regard to the conventional turbine. In this chapter, a computational study of a twisted Darrieus rotor was conducted through the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. Different grid sizes were investigated to assess the impact of grid generation on the computing findings. The validation of the computing method with antecedent tests was carried out to select the adequate grid size. The flow characteristics of the water around the twisted Darrieus rotor have been assessed and discussed.