One of the vertical axis wind turbines that utilize drag force is the Savonius wind turbine. Savonius wind turbines are characterized by low speed rotation and high torque, so they are rarely used for wind power generation and are used for pumping and milling. On the other hand, ocean current power generation, which has been attracting attention recently, has great potential, but there are few research examples and it has not been put into practical use. Since the ocean current is relatively slow, power generation using the Savonius type rotating device has great potential. Numerical simulation is effective for investigating the performance of the Savonius type rotating device, but in performing the numerical simulation, it is necessary to divide the area including the rotating device into a grid. Although the Savonius wind turbine has a simple geometric shape, it is not so easy to generate a grid suitable for analysis. In this report, we propose a grid generation method that can be applied even when multiple rotating devices rotate independently.