Fluid Deformation Induced by a Rotationally Reciprocating Impeller

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This study deals with fluid mixing process in the circular cross-section of a cylindrical vessel using a rotationally reciprocating (back and forth rotational) plate impeller from the view point of experimental visualization and numerical simulation. We have investigated the fluid deformation process with the visualization of streak line. It was found that a pair of vortices generated at the impeller tip plays a crucial role for stretching and folding of streak line. Additionally, for an effective overall mixing, we found that fluid needs to be dragged inward to the region near the mixing shaft, stretched and folded along the impeller plate, and then extensively deformed from the impeller tip. However, since the path of fluid inward motion was rarely disturbed by locally strong vortices generated at the condition of small amplitude and short period, a poor mixing region expanded from the mixing shaft to the vessel wall, which made two separated mixing regions in a vessel. As increasing amplitude, a poor mixing region was shrunk near the mixing shaft. At the case of the largest amplitude and longest period, fluid was effectively deformed everywhere in the vessel, which leads to a highly intensified mixing process.