Cavitation inception

Abstract

We are sure that the delegates to the present conference do not need to be reminded that cavitation inception in the pervasive role it occupies in Naval Architectural hydrodynamics remains as a basic problem bedevilling the worker in the laboratory and field alike. One of the more perplexing aspects of this phenomenon has been its lack of repeatability between experiments carried out on similar test bodies in different test facilities or even on different types of bodies in the same test facility. In addition, in sea trials, the conditions under which it occurs are seldom well defined. There is the further problem of accounting properly for the effects of modifying the test fluid itself either by a change in state point or by the addition of an additional liquid solute such as a long chain polymeric molecule or finely divided particulate matter. Underlying all these considerations is the ultimate goal of extrapolating laboratory findings to representative field conditions; in the present context, these are the various conditions of the marine environment. This specific point was addressed briefly in the concluding discussion on cavitation inception of the 16th conference in which the onus of reporting progress towards this goal was laid upon the present authors. It would indeed be gratifying to report to the present conference that our experimental techniques are now sufficiently advanced to simulate properly all of the important prototype conditions even if we had precise knowledge of them. This is, regrettably, not yet the case, but there have been nevertheless solid advances in certain areas of cavitation inception research which make one hopeful for the future. We have selected three such areas to report on to the present conference; viz, surface inception, vortex cavitation and scaling, and the effects of polymer additive on inception. In addition, we refer briefly to current methods of observation/measurement of cavitation nuclei as this is a subject of paramount importance to the cavitation process itself and also because we suspect such measurement will become an important part of laboratory testing in the near future. In the material to follow we have tried to emphasize the phenomena and techniques themselves leaving to a future occasion a full assessment of inception scaling theories. We have not attempted to be encyclopedic in coverage as there are recent excellent texts and survey articles, e.g. Arndt (1971), Eisenberg (1969), Eisenberg and Tulin (1961), Knapp et al (1970), Robertson and Wislicenus (1969) Grein (1973) which cover the field, and we should also state that in so doing any serious omissions we may have made are not intentional!

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