The air-entraining vortices appeared in a pump sump often exert a bad influence to the pump characteristics, and moreover generate loud noise and severe vibration of the pump shaft and pipe systems. To constrain the vortices, changing the flow pattern in the sump by inserting a board is often very effective, but excessive change sometimes ends with a reverse effect especially in the case of the nonuniform inlet flow conditions. In this paper, it is shown that the perforated board with an appropriate resistance, inserted into the water upstream of the suction pipe, changes the flow pattern moderately and constrains the generation of the vortex effectively, for both uniform and nonuniform inlet flow conditions.
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