Jetting of Viscous Single Droplets from Cavitation Induced Rayleigh-Taylor Instability

Cavitation bubbles oscillating inside liquid droplets can produce high speed liquid jets from the surface of the droplets. This type of jetting is induced by the spherical Rayleigh-Taylor instability, in which the radial acceleration is due to the oscillation of an internal cavitation bubble. The experiment is accomplished by levitating the droplet with an acoustic trap and creating a vapor bubble within the droplet with a pulsed laser. Using high speed photography, we observed jets emerging from the droplet surface which pinch off into finer secondary droplets. The phenomenon is then reproduced with a computational fluid dynamics (CFD) simulation model to study the jetting mechanism. Additionally, we developed an analytic model to calculate the droplet surface perturbations growth based on the spherical Rayleigh-Taylor instability, which allows to evaluate the surface stability over a large parameter space. The analytic model predicts correctly the onset of jetting as a function of Reynolds number and normalized internal bubble energy.