Study on cavitation inception in hydraulic oil flow through a long two-dimensional constriction

Abstract

It is known that the traditional ‘nucleus’ theory for cavitation is incompatible with certain facts physically and experimentally recognizable in oil hydraulic flows. In order to re-examine this issue, cavitation of hydraulic oil flow through a long two-dimensional acrylic constriction was observed by various techniques: stroboscopic photography with a microscope, laser beam transmission, pressure and noise measurements, and luminescence and electrical charge detection. It was revealed that, at the incipient stage of cavitation, one stationary microscopic cavity always emerges suddenly on the inlet edge. Light emission was also observed in the cavitation together with electrostatic charge. All the findings taken together, which cannot be consistently explained by nucleus theory, lead to the following hypothesis: at the separation point a tensile force rips a liquid particle from the wall, leaving behind a vacuum space, which forms the incipient stationary cavity on the edge.