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Bubble Dynamics
Bubbles can be found everywhere in our everyday life: we can clearly see them in a glass of sparkling water, or in a beer; their formation reveals that the water in a pot is boiling. After their formation (cavitation or boiling), the analysis of the complex dynamics of their expansion, migration into the fluid, coalescence and collapse, is an extremely challenging task to be addressed with theoretical modeling. The bubble dynamics is indeed a fascinating classical problem investigated since the pioneering work of Lord Rayleigh and several models with increasing level of complexity have been proposed in the last century. The increasing computational power has been a huge thrust to gain more insights and to analyze in more detail the bubble life by means of numerical simulations.

In our group a diffuse interface approach is used to describe, at a mesoscopic scale, the dynamics of the two phase system with the vapor bubbles immersed in the liquid. In this context, the interface between the two phases, is not treated as a discontinuity but as a narrow layer where the physical properties of the fluid varies rapidly but continuously. This allow a very accurate description of all those interfacial phenomena like break-up and coalescence where topological changes occur.

In particular we recently tackled the problem of bubble collapse, with all the related complex acoustic phenomena like shockwave emission. The diffuse interface approach has demonstrated an invaluable tool to describe the most fine details of the bubble dynamics and the consequences on the surrounding liquid.

Successive snapshots of the system configuration during the collapse of a spherical vapor bubble immersed in an over-pressured liquid (Rayleigh collapse). Density field (upper row) and pressure gradient intensity (lower row).  The plots in the lower row highlight the position of bubble interface and radiated shock. For more details see (F. Magaletti et al., 2015, Phys. Rev. Lett. 114 (6).)

Snapshots during the collapse 
of an axisymmetric vapor bubble
near a wall.
The presence of the wall breaks
the symmetry and causes the
formation of a liquid jet toward
the wall.
The complex shock pattern
is highlighted. For more details
see (F. Magaletti et al., 2016,
Int. J. Multiphase Flow 84.)