Extensional Flow of Liquid Jets Formed by Bubble Collapse in Cavitating Motor Oils

We report experiments involving a technique which provides a means of studying liquid jets which are formed by the collapse of a gas bubble under cavitation-generated shockwaves. The results obtained for such jets formed from a multigrade oil establish that the liquid experiences a significant degree of extensional deformation, at high rates of extension. The results support the conclusion that the reduced velocity and final length of such jets, relative to their Newtonian counterparts, is due to an increased resistance to extensional flow. Insofar as the multigrade oils studied here are made viscoelastic by polymer additives and evidently possess significant levels of resistance to extension, the results provide clear evidence in support of the ‘mitigating effect’ of viscoelasticity on a cavitation damage mechanism mooted by Berker et al (1995).