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An experimental study is reported of liquid jets formed by the collapse of bubbles under cavitation-generated pressure waves. The results reveal that jets formed from samples of commercial multigrade engine oils experience an extensional flow which is characterized by high rates of extension, the latter being relevant to considerations of the flow of oils within dynamically loaded journal bearings. Contrary to previous indications in the literature, commercial multigrade oils are found to exhibit significantly larger resistance to extensional flow than their Newtonian counterparts and, 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 evidence in support of a mitigating effect of viscoelasticity on a cavitation damage related mechanism, as mooted by Berker, Bouldin, Kleis and Van Arnsdale.

We report measurements of the tensile strength, F c , of dilute polymer solutions, involving tension pulses of ca. 200–300 μs duration, and stressing rates of ca. 1–10 bar/μs: Contrary to previous indications in the literature, the tensile strength of polyacrylamide (PAA) solutions under pulsed dynamic stressing is found to increase with increasing polymer concentration. This accords with the results of a study of the effect of PAA concentration on the development of liquid jets, which are formed by bubble collapse in dilute PAA solutions: a marked reduction in jet length and velocity is found due to the presence of PAA. Estimates of the tensile stresses supported by the stretching jets are commensurate with the results obtained in measurements of F c .

This paper describes a study of the formation of liquid jets in elastic and Newtonian liquids. The technique used to study this phenomenon involves a shock wave, emanating from the collapse of a cavitation bubble, which causes a gas bubble underneath the free surface of a liquid column to collapse, thereby producing a liquid jet. A comparison of the jets formed by commercial multigrade motor oils and their Newtonian counterparts shows that, in the former, liquid jet production is markedly suppressed, with up to an order-of-magnitude reduction in length being recorded. Similar findings are made when elastic `Boger' liquids and their Newtonian counterparts are compared.

A technique for studying the production of liquid jets by cavitation bubble-shockwave interaction near a free surface is presented. Despite its extreme simplicity, the technique reveals striking phenomena which have importance in several areas of engineering, and offers advantages over those techniques used in previous studies.

We report a study of liquid jets formed by the collapse of bubbles under cavitation-generated pressure waves. Such jets involve an extensional flow which is characterized by high rates of extension, the latter being relevant to considerations of the flow of oils within dynamically loaded journal bearings. The technique reported here is found to be sensitive to the influence of extremely small concentrations of high molecular weight polymeric additive (xanthan gum). Commercial multigrade oils are also found to exhibit significantly larger resistance to extensional flow than their Newtonian counterparts and, insofar as the multigrade oils studied here are made viscoelastic by polymer additives, and possess significant levels of resistance to extension, the results provide evidence in support of a mitigating effect of viscoelasticity on cavitation, as mooted by Berker et al. [3].

We report the results of recent experimental work involving the formation of low shear viscosity liquid filaments by the collapse of a gas bubble under a cavitation-generated shockwave. The filaments experience a significant degree of extensional deformation, at high rates of extension (typically within the range 1000 s' to 5000 s - 1 ) which are relevant to considerations of journal bearing lubrication. The results of experiments conducted on samples of commercial multigrade engine lubricants in the SAE 15W-40 and 5W-30 viscosity grades 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 SAE category (15W-40) 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.