This research was carried out by adding a circular or elliptical cylinder beside the advancing blade to create a nozzle effect on the flow. An ellipse cylinder allows the wind to pass through a slightly longer path so that frictional losses increase which causes a pressure drop behind the advancing blade. The pressure difference between the front and rear sides of the advancing blade will increase, so the pressure drag acting on the advancing blade will also increase. The difference in the drag force of the advancing and returning blades will also increase so that the positive torque of the wind turbine and the turbine power increase. This research used a 2D numerical method using the ANSYS 2021 R2 software with meshes selected from the grid independence test process. The simulation uses a k-ω SST model. In this research, the ratio of vertical cylinder diameter to turbine diameter (Y/D) is 0.5, the distance from the centre of the wind turbine to the centre of the cylinder (T/D) is 1.50, and the flow velocity is 5 m/s. A circular or elliptical cylinder placed beside the advancing blades varies in cylindrical shape, namely the diameter ratio (Y/X) of 1/8, 1/4, 1/2, and 1. The simulation results show that Y/X = 1/2 has the maximum performance compared to turbines with other cylinder shapes. However, this configuration is still less than the performance of the Savonius wind turbine without cylinders. This is because the distance T/D = 1.50 is still considered too close, so blockage tends to occur in the gap between the cylinder and the advancing blade.