Experimental Investigations of Incipient and Desinent Cavitation

Abstract

Experiments with water in a high speed recirculating water tunnel were undertaken to measure the pressures at which incipient and desinent cavitation occurred. Incipient cavitation is defined as the onset of cavitation; desinent cavitation is defined as the cessation of cavitation. The two lucite test sections used formed the minimum area region of the nozzle in the water tunnel. One test section had a smoothly changing internal contour and the other had an abrupt contour change at the entrance to the cylindrical throat region. Cavitation in the abrupt contour occurred at the throat entrance at higher pressures than the cavitation pressures in the smooth contour. The cavitation in the smooth contour occurred at the entrance to the diffuser part of the nozzle. It was concluded that the cavitation pressures and cavitation numbers increased with velocity, the increase being greater for the abrupt contour with the exception of minimums indicated at incipient conditions in the abrupt contour at throat velocities near 88 ft/sec. A notable difference between the incipient and desinent cavitation numbers and pressures occurred for the abrupt contour, but not for the smooth contour using the techniques described for identifying the incipient and desinent cavitation regimes.