Wind turbine performance can be increased by using the optimum shape of the blade. Most of the previous numerical studies on Savonius wind turbine simulation used constant angular velocity as input data. Usually, the value of constant angular velocity was obtained from experimental data. In the actual case, the rotation of the rotor, i.e. the angular velocity of the blades, results from the interaction between fluids around the wind turbine with the turbine blades, in which there are changes of the moment of inertia. Rotation of the wind turbine can be simulated using the fluid-structure interaction method with one-degree of freedom. This study compares the performance of a rotor turbine using straight Savonius blades, to that using the Icewind turbine blades. In the steady and unsteady simulations, fluid was defined as incompressible, viscous, and uniform air which flow from inlet free stream. The simulation object rotates in one-degree of freedom in the overset mesh area. Icewind turbine generates higher coefficient power compares to the standard Savonius turbine, when it operates at very low wind speed, with the inlet free stream velocity below 4 m/s. This phenomenon is affected by the unsymmetrical shape of Icewind which allowed the fluid flow behind the reversing blade and sweep away the wake area, particularly effective at very low wind speed. The Savonius wind turbine, which is configured with endplates and overlap blades, rotates in high angular velocity and generates the highest peak coefficient of power. Fluid from the advancing blade is flowing through the overlap. The overlap flow fills the wake area and reduces backflow behind the reversing blade.