Observation of cavitation inception in hydraulic oil flow

It has been known that the traditional "nucleus" theory for cavitation is incompatible with some physically and experimentally recognized facts. In order to re-examine the issue cavitation in a hydraulic oil flow through a long two-dimensional acrylic constriction has been observed by strobos-copic photography with a microscope, laser beam transmission and pressure and noise measure ments. A revelation was that at the very incipient stage of cavitation, a microscopic cavity suddenly emerges and attaches on the inlet edge. Luminescence was also observed in the cavitation together with electrostatic charge. All the findings, which cannot be consistently explained by the nucleus theory, lead to the following speculation; at the separation point a tensile force rips off a liquid particle from the wall, leaving behind a tiny vacuum vecancy, which forms the incipient cavity on the edge. This rip-off action also results in electrostatic charges, which cause light emission when discharged in the vacuum.