CRITICAL JETS IN SURFACE-WAVES AND COLLAPSING CAVITIES

In certain types of collapsing cavities, a highly accelerated inward j et can occur. In other cases, starting from slightly different initial conditions, there is no jet but instead a small bubble is pinched off from the main cavity. At critical values of the initial parameters, s eparating inward jet formation from bubble pinch-off, the local flow h as been found to be self-similar; the axial acceleration increases lik e (t(1)-t)(-alpha), where t(1) is a critical value of the time t and a lpha is a positive constant. In this paper we report calculated values of alpha for three different classes of initial flows, namely (1) a m oving sink in an infinite fluid, (2) a bubble collapsing near a plane wall and (3) a slightly deformed bubble in an infinite fluid, with gra vity. These flows are all axisymmetric. The two-dimensional jets arisi ng from the impact of surface waves on a plane wall are also discussed and modelled.