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Cavitation across scales: following Bubbles from Inception to Collapse

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

Goal of BIC, “Cavitation across scales: following Bubbles from Inception to Collapse”, is developing innovative tools to increase our understanding of cavitation. Motivated by engineering applications, BIC deals with the complex physics taking place at different scales, from the microscopic scale where cavitation is initiated by the nucleation of nanometer-sized bubbles, to the macroscopic scale where bubbles are transported and interact with the macroscopic flow field. The project is conceived as a modeling effort aimed at providing an exhaustive description of cavitation combined with a subsidiary experimental activity run in parallel with the theoretical and simulative core. The five year effort involved a significant number of researchers among faculty members, PostDocs and Phd Students.

BIC explained the catalytic effect of surface geometry and chemistry on bubble nucleation and assessed the asymmetrical role of inertia in water intrusion/extrusion in/from surface asperities. Effective nucleation models permitted functional surface design, opening the way to applications of nanoporous materials for use in dampers, shock absorbers and energy accumulators. BIC solved the Salvinia paradox, explaining how this water fern keeps a stable gas layer attached when fully submerged, of potential interest for drag reduction.

BIC contributed to the field of bubble transport in turbulence by devising a novel methodology to accurately and efficiently account for the reciprocal momentum coupling between carrier fluid and bubbles/particles. The formulation can be combined with existing flow solvers for the Navier-Stokes equations and is generalized to the interaction between temperature/concentration fields and particles to exploit complementary areas such as those where condensation and evaporation are strongly coupled to turbulence.

BIC developed a continuum model bridging the gap from nucleation to the strongly non-linear phase of bubble-bubble interaction, coalescence and collapse. The novel approach, based on a phase-field model endowed with thermal fluctuations in the spirit of Landau and Lifshitz’s fluctuating hydrodynamics, is a powerful tool directly extended to complementary fields, e.g. boiling and heat transfer management. It can be implemented on solvers using unstructured grids, so as to allow for local grid refinement and efficiently deal with complex geometries.

On the experimental side, beside basic experiments with Laser induce bubbles both far from and close to surfaces, a new pressure sensor based on photonic technology has been developed to detect bubble collapse-induced shocks. An unexpected outcome concerns cavitation induced reversible endothelium permeabilization. The novel microfluidic platform endowed with a physiological endothelium to mimic actual blood vessels, a so-called vessel-on-a-chip, will be further developed thanks to the ERC Proof-of-Concept grant INVICTUS.

In conclusion, BIC stands out as a successful effort to integrate several interdisciplinary skills ranging from fluid dynamics, statistical mechanics, advanced numerical techniques, photonics and biology to provide an unprecedented comprehensive view of cavitation across the scales.