Particles and Fields in Turbulence and in Complex Flows


14/09/21 *** NEW fellowship available at University of Torino: check the "News" section for more information  ***



   Turbulence is a ubiquitous phenomenon appearing in very different systems over an extremely wide range of scales, from microns to kilometers. In this sense turbulence is not a single problem, but rather a huge field of interdisciplinary research with applications to different disciplines. For example state of the art simulations of turbulent flows under rotation (see Fig. 1), are not only applicable to real-life situations such as weather systems but also provide insight into the theoretical model itself.


The FieldTurb initiative is focused on the problem of "Particles and Fields" transported by, and interacting with, complex and turbulent flows. The aim of the project is to gain a better understanding of fundamental questions involving general problems of classical field theories of out-of-equilibrium systems at macro-, micro- and nano-scales, as well as of many applied problems involving, e.g. energy production and transfer, interface functionalization and autonomous navigation.


The challenge is to export the knowledge and methodologies developed for the ideal case of Newtonian turbulence to the case of suspensions, foams and emulsions. In general, the objects transported by the flow possess internal degrees of freedom, such as elastic polymers, fibers (see Fig.2), or complex particles. One important question is to understand which kind of turbulence emerges from the interactions between the complex constituents of the fluid, and its degree of universality with respect to the detailed microscopic model.


    The behaviour of particles in complex flows becomes particularly intriguing when particles are active probes, in the sense that they optimise trajectories with respect to some prefixed strategy, or simply because they are self-propelled objects (bacteria, biological filaments, artificial swimmers). Both classes of systems pose important challenges from the fundamental point of view of out-of-equilibrium statistical mechanics and open the doors to new generations of devices.


 Moreover, self-prolusion makes the collective dynamics of active particles dramatically different from that of their passive analogues, with new unexpected behaviour such as aggregation in absence of attractive forces, super-fluidic rheological response, spontaneous flow and new motility modes (see Fig. 3).


Another line of research, boosted by recent experimental results, is the study of turbulence in quantum fluids. Chaotic/turbulent-like regimes can now be observed in many different superfluid systems, including helium and atomic Bose-Einstein condensates (BECs).

 Figure 4. The figure shows an array of vortices rotating in a superfluid described by the Gross-Pitaevskii equation. The panel on the left shows the contour of the module of the wave function, while the panel on the right the phase.


Within FieldTurb both theoretical and numerical approaches are used to study 3D and 2D quantum fluids (Fig. 4), to assess fundamental universal statistical features of their dynamics. 


All these problems are tackled by combining traditional tools of theoretical physics with emerging tools at the interface between material science and biology, particularly for active matter applications where new physical concepts arise (e.g. jamming, topological defects). The theoretical approach is complemented by numerical simulations and data analysis, featuring innovative techniques of Machine Learning (ML).


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