CRITICAL MICROJETS IN COLLAPSING CAVITIES

Inward microjets are commonly observed in collapsing cavities, but her e we show that jets with exceptionally high velocities and acceleratio ns occur in certain critical flows dividing jet formation from bubble pinch-off. An example of the phenomenon occurs in the family of hows w hich evolve from a certain class of initial conditions: the initial fl ow field is that due to a moving point sink within the cavity. A numer ical study of the critical flow shows that in the neighbourhood of mic rojet formation the flow is self-similar. The local accelerations, vel ocities and distances scale as t(beta-2), t(beta-1) and t(beta) respec tively, where beta = 0.575. The velocity potential is approximately a spherical harmonic of degree 1/4.