Moderate cavitation was used to visualize the tip clearance vortex in a highly-loaded single-stage axial-flow pump. Two different techniques were utilized to produce photographs and videos. From these it was found that for flow rates lower than design an initially well defined clearance vortex undergoes spiral-type vortex breakdown. This result was theoretically confirmed in an approximate manner by solving the Bragg and Hawthorne equation for an isolated vortex with a measured casingwall pressure distribution as a prescribed boundary condition.

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