ON THE COLLAPSE OF VAPOR CAVITIES IN A THIN LIQUID LAYER UNDER HIGH-PRESSURE TRANSIENT

An apparatus was built in conjunction with the transparent anvils drop weight machine to view the events occurring during the formation, gro wth, and collapse of vapour cavities in thin liquid layers. During the collapse phase, several mechanisms operate, namely: proportional shri nkage, volume jetting, surface jetting and secondary cavitation: which can be attributed to features of the liquid flow under compression. L ocalized flow in the bodies of the liquid surrounding the cavities dri ves the proportional shrinkage (in which the cavities roughly retain t heir shapes); the pressure or shock waves propagation and reflection a t the cavity interfaces drive the volume jets; the interaction of the release or rarefaction waves with the pressure/shock wave itself seems to initiate the secondary cavitation End the surface jets seem to be caused by the variations of the vertical distribution of the horizonta l flow velocity during the transition from the tensile to the compress ion phase. A simple model which considers the liquid a perfectly plast ic material and assumes a very rapid rate of vapour condensation fits the experimental results throughout most of the collapse process. It s eems that in the final stages of the collapse the rate of condensation is not fast enough and the model is not valid there. Further studies should be carried out to better quantify the various mechanisms observ ed.