The effect of adding inner blades to the Savonius turbine deserves extensive attention due to its promising enhancement to its performance. A numerical study was carried out to investigate the effects of different radii and angles of additional inner blades on the performance of Bach-type rotor at different tip speed ratio (TSR). In the present work, two different studies were performed for a number of cells, domain size and time step. The best numerical model was then used to investigate the effect of the additional inner blades on the Savonius rotor performance. Additional inner blades radii and angles were investigated from 0.25 to 0.85 times original blade radius and 70° to 160° respectively. The best improvement of rotor performance with additional inner blades are higher than values of conventional one by 27.77% at tip speed ratio TSR = 0.75 up to 44.5% at TSR = 0.25.