High Deformation Rate Uniaxial Elongation Flow of Mobile Fluids in Cavitation Bubble Collapse Experiments

We report experimental work involving the rapid uniaxial elongation of jets of mobile (i.e. low shear viscosity) liquids formed by the collapse of a gas bubble under a cavitation-generated shockwave. The results of this work establish that the jets experience a significant degree of extensional deformation, at high rates of extension (typically > 1000 s⁻¹) which are relevant to considerations of journal bearing lubrication. The results of experiments conducted on samples of commercial multigrade motor lubricants in the 15W40 category indicate a substantially increased resistance to extensional flow when compared with the behaviour of their Newtonian counterparts. Interestingly, the technique is able to distinguish between the rheological properties of lubricants of identical category (15W40) which are formulated for use in different engines (petrol engine and diesel engine, respectively). The lubricant formulated for the latter application is found to exhibit the highest resistance to extensional flow.