Effect of pre-rotation on cavitation in centrifugal and mixed flow pumps.

Abstract

It has been theoretically shown that introduction of prerotation at the impeller inlet at design point improves the cavitation performance. A qualitative assessment of this from existing data on centrifugal pump impellers has been made. Several mixed-flow impellers have been designed and tested; it has been shown that a free-vortex prerotation considerably improves the cavitation performance of a mixed-flow pump whereas a forced-vortex prerotation worsens it. Some experiments have been conducted on centrifugal pumps existing in the laboratory and several curious phenomena hitherto not reported by observers have been noticed and explained on the basis of other experimental facts. Chapter I describes the phenomenon and mechanism of cavitation. It also gives the methods of observation of cavitation in pumps and of finding when its inception occurs. It briefly deals with the mechanism of cavitation damage, and some methods of minimizing it. Chapter II outlines the importance of scale model tests for cavitation and states the underlying theory. It describes several cavitation numbers put forward by various authors and their viewpoints on cavitation scale effects, and points out the mutual contradiction between them.