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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 a study of liquid jets which are formed by bubble collapse under cavitation-generated pressure waves. The results obtained for jets formed from samples of a multigrade motor oil provide the first evidence that such jets experience 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 evidence in support of a mitigating effect of viscoelasticity on a cavitation damage mechanism, as mooted by Berker et al. (J Non Newton Fluid Mech 56:333, 1995).

This paper describes experiments in which a shock wave, emanating from the collapse of a cavitation bubble, causes a second bubble to collapse, thereby producing a liquid jet. A comparison of the jets formed by bubble collapse in dilute solutions of polyacrylamide and polyethylene oxide, and in their Newtonian counterparts, shows that in the polymer solutions liquid jet development is markedly suppressed. The implications of these findings are discussed in the context of cavitation damage.

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 .

We report experiments in which the interface between two immiscible liquids is subjected to tension by dynamic stressing. During the course of these experiments, cavitation is only observed in the stronger of the two liquids (in terms of their tensile strength). The results are explained in terms of the failure of the liquid-liquid interface under tension, and the ability of the vapour layer so created to reflect subsequent compressional waves as tension. The findings reported here support the results of earlier work in this area and their technological implications are briefly discussed.

We present experimental evidence to support a claim of Temperley and Trevena that, in the dynamic stressing of water by tension involving low–frequency ultrasound pulses, no serious discrepancy exists between theory and experiment. Experiments conducted on samples of deionized water suggest that this liquid can sustain a transient tension of up to ca. 700 bar under dynamic stressing by pulses involving a stressing rate of ca. 10 bar 𝛍s –1 , in order–of–magnitude agreement with predictions of nucleation theory. In these experiments, tension pulses generated by the reflection of compressional waves from the free surface of a vertical column of water are found to propagate at a velocity appropriate to the vapour, where the amplitude of the pulses is sufficient to provoke cavitation of the liquid. Photographic evidence of this cavitation shows that it can occur in the body of the liquid, a feature of the experiments that, in addition to the high rate of stressing, may account for the relatively high values of tensile strength reported here.

We report findings from studies of water subjected to tension by pulsed dynamic stressing which may have significance in the context of assessing the safety of biomedical applications of low-frequency ultrasound. When incident on bubbles near a free surface (or a flexible membrane), shockwaves generated by cavitation bubble collapse are found to lead to the production of liquid jets which are directed towards the surface. Tension pulses generated by reflection of these shockwaves at a free surface initiate, and propagate, the growth of further cavitation bubbles. Estimates of the tensile strength of water, Fc, from measurements of the velocity of these pulses suggest that Fc is far higher than has previously been reported for experiments involving the reflection of low-frequency ultrasound; and the estimate of Fc reported here considerably exceeds the values of tension thought to be generated by ultrasound in many biomedical applications.

We report experiments in which liquid mercury is subjected to tension by dynamic stressing, involving pulses of ca s duration, and stressing rates of approximately 1 bar . Under these conditions, the tensile strength of liquid mercury is found to be ca 2500 bar. These results are markedly lower than those obtained in experiments involving shorter pulse durations, and support the conclusion of other workers that in the dynamic stressing of liquids by tension, the higher the rate of stressing, the higher the measured value of tensile strength.

An instrument which exploits the `tube-arrest' technique of subjecting a column of liquid to tension by dynamic stressing is described. In this apparatus two tension pulses are produced, one ab initio within the liquid, the other by free-surface reflection of a cavitation-generated shock wave. A method of deriving the tensile strength of a liquid from measurements of the velocity of these pulses is presented, and previous assumptions concerning the origin of tension in the `tube-arrest' technique are critically examined. The initial tension pulse is shown not to arise at the bottom of the liquid column as has been assumed hitherto, and the means by which cavitation is exploited to study the production of liquid jets by shock wave-bubble interaction are explained.

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.

An experimental study of the origin and hitherto unexplored structure of the pressure - tension cycles accompanying the cavitation of liquids under dynamic stressing by tension is presented. The results of this study are relevant to certain problems in engineering and medicine, and the potential for application of the improved `tube-arrest' apparatus described here to those fields is considered.

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.

Measurements of the velocity of tension pulses arising from the reflection of compressional waves from the free surface of water confirm predictions concerning the acoustic properties of a metastable transition layer (Temperley and Trevena 1979, 1987, 1994). This liquid-vapour layer, which leads to a reduction in the effective speed of sound, constitutes a source of cavitation nuclei. Accordingly, values of the tensile strength of water, Fc, derived from tension pulse velocities are commensurate with the lowest values in the range of theoretical estimates (∼ 600 bar).