When a thin flat pate is released in still air, the plate automatically sets into a rotational motion. This phenomenon is called autorotation. The autorotating flat plate is loaded by unsteady fluid-dynamic forces. It is guessed that the forces are contributed by one due to vortex shedding from the edges of the plate and one due to the plate rotation, but the detail force characteristics have not been clear yet. In this study, we calculated the two types of flow by the discrete vortex method, one is flow around a rotating flat plate hinged about its center at constant rotating frequency in the uniform flow and the other is flow around a freely falling flat plate. The computed result in both types of flow agree well with the experiment. In the case of freely falling plate, autorotation phenomena could be predicted. By computed fluid dynamic forces, the contributions of vortex shedding from the plate to fluid dynamic forces and feedback effect of the fluid dynamic forces were found.

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