The accumulation mechanism of cells in a rotational culture device is investigated from the viewpoint of fluid mechanics. For simplicity, the deformation of the water surface is neglected and the cells are treated as spherical solid particles. From the numerical simulation of flow field with typical parameters used in the previous experiments, it is confirmed that the relative velocity of fluid induced by the rotational shaking is much smaller than the speed of rotation. From the analysis of particle equation of motion, it is found that the accumulation of cells toward the central region is found to be due to the interaction between the acceleration by rotational shaking and the drag force acting on the cells. The integral time scale for cell accumulation was estimated to be about 10 min for typical cases. The accumulation speed increases quadratically with the diameter of cell and the angular velocity of rotational shaking, which qualitatively support the previous experimental observation.
