Rotating cavitation in three and four-bladed inducers

Abstract

Recently, rotating cavitation occurred in the inducers of propellant feed pumps during the development of large advanced rocket engines, such as the LE-7, Ariane 5, and the Space Shuttle Main Engine. With regard to suction and overall performance, some comparisons have been made as to the numbers of blades. For example, it was reported that good suction performance was obtained with a small number of blades and that a three-bladed inducer is preferable if design considerations permit. Furthermore, it is well known that alternate blade cavitation occurs in the four-bladed inducer. However, it was recently clarified that attached cavitation or steady asymmetric cavitation occurs in the three-bladed inducer. Attached cavitation causes radial thrust due to an asymmetric pressure distribution around the periphery of the inducer inlet, while alternate blade cavitation does not cause radial thrust due to symmetric pressure distribution. We performed further experiments to investigate the difference of rotating and attached (or alternate blade) cavitation between three- and four-bladed inducers which had almost the same dimensions.