Influence of the Tip Clearance on the Auto-Oscillation Frequency of a Cavitating Pump
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This paper gives a contribution to the vortex structure, vortex dynamics and the tip clearance inertance as well as compliance of a cavitating pumps. The related vortex structure is reduced to the blade bound vortices, hub vortex and tip vortices only. At heavy part load φ → 0, the tip vortices form a coaxial vortex ring of increasing strength. This vortex ring may break down to several wall bound vortices at severe part load. The velocity potential of the vortex ring is given by the Bessel series solution and applying a limit value analysis. The inertance of the gap flow is derived straight forward from this generic mathematical model of an axial pump at deep part load. With the compliance due to cavitation, the natural frequency of cavitation surge is discussed for the given generic mathematical model of the pump.