Cavitation bubble nucleation induced by shock-bubble interaction in a gelatin gel

Abstract

An optical visualization technique is developed to study cavitation bubble nucleation that results from interaction between a laser-induced shock and a preexisting gas bubble in a 10 wt% gelatin gel; images of the nucleated cavitation bubbles are captured and the cavitation inception pressure is determined based on Euler flow simulation. A spherical gas cavity is generated by focusing an infrared laser pulse into a gas-supersaturated gel and the size of the laser-generated bubble in mechanical equilibrium is tuned via mass transfer of the dissolved gas into the bubble. A spherical shock is then generated, through rapid expansion of plasma induced by the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gel under tension that results from acoustic impedance mismatching at the bubble interface interacting with the shock. We measure the probability of cavitation inception from a series of the repeated experiments, with varying the bubble radius and the standoff distance. The threshold pressure is defined at the cavitation inception probability equal to one half and is calculated, through comparisons to Euler flow simulation, at −24.4 MPa. This threshold value is similar to that from shock-bubble interaction experiments using water, meaning that viscoelasticity of the 10 wt% genatin gel has a limited impact on bubble nucleation dynamics.

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