Community Research and Development Information Service - CORDIS


BIC Report Summary

Project ID: 339446
Funded under: FP7-IDEAS-ERC
Country: Italy

Mid-Term Report Summary - BIC (Cavitation across scales: following Bubbles from Inception to Collapse)

Bubble nucleation, evolution and collapse are phenomena occurring in natural systems and human-developed devices. Depending on the case, nucleation and collapse are positive phenomena to be enhanced (e.g. gas bubble enhanced drug delivery) or negative processes that must be prevented (e.g. the damages caused by cavitation on propellers blades).
Cavitation involves several physical aspects acting at different time and spatial levels, ranging from the nanometric scale where chemistry and topography of surfaces affects nucleation up to the millimetric length scale where bubbles are deformed and transported by the flow.
During the first half of the project the research activities have been focused on the analysis of the individual phenomena characterizing cavitation (i.e. nucleation, transport, collapse), each one addressed with the most suitable technique. Important results have been achieved regarding all these distinct aspects of cavitation.
Concerning nucleation, by extending advanced techniques of rare events, general design principles to control bubble formation have been identified. These principles can also explain the complex structures observed in nature, on the leaves of plants and skins of animals (insects, spiders, etc), such as the combination of hydrophobic and hydrophilic domains in floating plants, and the complex texturations of their surfaces.
Once bubbles are formed they eventually grow up and are transported by the flow. In order to address bubble transport in turbulent flows, the group developed a novel numerical technique, the Exact Regularized Point Particle (ERPP) method. Simulations showed that bubbles transported by turbulent flows tend to segregate forming small scale clusters in the low pressure regions of the flow. It means that the bubbles locally back-react with the carrier flow thus determining an alteration of the turbulence dynamics and, as a consequence, an alteration of their clustering properties.
During transport the bubble can cross regions of higher pressure causing a very fast collapse which is known to be associated with shockwave emission and cavitation structural damage on nearby objects. This phenomenon has been investigated in detail through numerical simulations, by extending diffuse interface models. The results allowed to explain the mechanism leading to the shockwave emission and its interaction with solid walls.
The theoretical and numerical studies have been supported by experimental activities. At first, several expertise have been acquired and the experimental setup has been designed and realized. Thanks to proper techniques for microfluidics, such as micro Particle Image Velocimetry, high speed imaging, pressure measurements and fluorescent microscopy, the main physical aspects of cavitation have been investigated. In particular, a bubble generated by focusing a pulsed laser in a volume of water is analyzed, starting from the breakdown induced by the energy deposition and generation of plasma, to the origin of a vapor bubble, its expansion and successive collapse. Moreover the emission of shock waves and their pressure fingerprint have been measured through a purposely designed optical device. Finally, an application to biomedical systems is being analysed. In particular the permeability of endothelial walls is enhanced and controlled by inducing bubbles oscillation and cavitation. This phenomenon is investigated in a custom made micro-device by a fluorescent microscopy based method.
The intrinsic multiscale nature of cavitation phenomena asks for a cross-coupling of all these techniques. This is the subsequent goal the group is working on. Some of this kind of inter-connection has already been set up, such as the use of extended fluctuating hydrodynamics to embed atomistic detail within the bubble dynamic on microscopic length scale, and are ready to be exploited.

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