Within the framework of the E-Nucl project, and in collaboration with the group of G. Eyink at Johns Hopkins,  we investigated the emergence of non-equilibrium long-range correlations in concentration fluctuations during the free diffusion of a solute in a solvent. While such correlations are well established experimentally, their dynamical origin has remained unclear. To address this problem, we adopted the model proposed by Donev, Fai, and Vanden-Eijnden (DFV), derived from the high-Schmidt-number limit of the Landau–Lifshitz fluctuating hydrodynamics for binary mixtures. Starting from an initially sharp concentration interface in an unbounded domain, we combined analytical arguments and numerical simulations using tools from turbulence theory. The results reveal the spontaneous emergence of a quasi-steady, self-similar regime in which concentration correlations exhibit distinct spatial scalings at short and large distances. Specifically, the well-known regime of “giant concentration fluctuations” is complemented by a newly identified regime characterised by algebraic decay at large separations. The study provides fresh insight into the dynamic mechanisms underlying non-equilibrium correlations and offers quantitative predictions that can be directly tested in experiments.

Within the E-Nucl project, we uncovered complex transition pathways for vapour bubble nucleation in metastable liquids, under both homogeneous and heterogeneous conditions. The study, published in the Journal of Fluid Mechanics (Gallo et al., “Complex transition pathways in boiling and cavitation”), combines Navier–Stokes–Korteweg dynamics with rare-event techniques to resolve transition mechanisms and nucleation times. The results show that nucleation pathways deviate significantly from classical theory: bubble volume alone is not a sufficient reaction coordinate, as the process is driven by long-wavelength fluctuations with densities close to the metastable liquid. We further propose a hydrodynamics-based strategy to infer nucleation times, validated against state-of-the-art theories. The analysis reveals non-trivial effects of surface wettability on heterogeneous nucleation, including homogeneous nucleation persisting at moderate hydrophilic wettabilities, while hydrophobic walls anticipate the spinodal. Although demonstrated for a prototypical fluid, the approach is general and can be extended to complex geometries and real fluids, paving the way to predictive modelling of nucleation in engineering systems.

Mirko Gallo, Carlo Massimo Casciola

Mirko Gallo, Francesco Magaletti, Anastasios Georgoulas, Marco Marengo, Joel De Coninck, Carlo Massimo Casciola

Mirko Gallo, Francesco Magaletti, Carlo Massimo Casciola

Mirko Gallo, Francesco Magaletti, Davide Cocco, Carlo Massimo Casciola