high-energy, quantum and soft matter, and industry applications
DIEP focus session on hydrodynamics | 21st January 2020 | Physics@Veldhoven
Organizers and chairs: Jácome Armas and Jan de Boer
An invitation to hydrodynamics
Hydrodynamics is an emergent description of near-equilibrium thermodynamic systems and applicable to a wide range of phenomena, including heavy-ion collisions at particle accelerators, flows in strongly correlated quantum systems such as graphene or dynamics of microtubule-kinesin suspensions on droplets. Recently, hydrodynamics has undergone a fast-paced change revolutionising our perspective of it. This revolution is a consequence of key developments in the formulation of hydrodynamic theories, on flows on curved geometries, in numerical techniques for tackling turbulence, and in experimental methods for detecting electron flows. This focus session covers many of these developments, including the emergent field of viscous electronics and the role of complex fluids in industrial cosmetics. The session features world expert G. Falkovich, known for bridging quantum and soft matter, and talks by U. Gursoy, L. Giomi and F. Toschi on particle collisions, curved surfaces and turbulence.
Wonders of viscous electronics
Gregory Falkovich, Weizmann Institute of Science
Quantum-critical strongly correlated systems feature universal collision-dominated collective transport. Viscous electronics is an emerging field dealing with systems in which strongly interacting electrons flow like a fluid. Such flows have some remarkable properties never seen before. I shall describe some recent theoretical and experimental works devoted, in particular, to a striking macroscopic DC transport behavior: viscous friction can drive electric current against an applied field, resulting in a negative resistance, recently measured experimentally in graphene. I shall also describe conductance exceeding the fundamental quantum-ballistic limit, freely-flowing viscous flows, field-theoretical anomalies and other wonders of viscous electronics. Strongly interacting electron-hole plasma in high-mobility graphene affords a unique link between quantum-critical electron transport and the wealth of fluid mechanics phenomena.
Relativistic hydrodynamics is central to the study of strongly interacting plasmas, in particular to the quark-gluon plasma produced in the heavy ion collisions and expected to be created in mergers of binary neutron stars. In most of its realisations in Nature the quark-gluon plasma is produced along with enormously strong magnetic fields. This renders magnetically generated phenomena — such as the electric and chiral currents induced by quantum anomalies and magnetically induced hadron flow — essential elements in transport of heat and charge in this system. I will describe recent theoretical developments in relativistic magnetohydrodynamics and its predictions for charged hadron distributions together with the latest experimental status.
We investigate the turbulent dynamics of a two-dimensional active nematic liquid crystal constrained to a curved surface. Using a combination of hydrodynamic and particle-based simulations, we demonstrate that the fundamental structural features of the fluid, such as the topological charge density, the defect number density, the nematic order parameter, and defect creation and annihilation rates, are approximately linear functions of the substrate Gaussian curvature, which then acts as a control parameter for the chaotic flow. Our theoretical predictions are then compared with experiments on microtubule-kinesin suspensions confined on toroidal droplets, finding excellent qualitative agreement.
Geometrical control of active turbulence in curved topographies
Turbulent flows are well know for their chaotic dynamics characterised by non-trivial, multi-scale and multi-time correlations of hydrodynamics stresses. Stabilised emulsions are complex fluids made by droplets of one fluid dispersed into another immiscible fluid. Their internal structure gives stabilised emulsions rheological properties ranging from those of a simple viscous Newtonian fluids to those of an elastic solids. The presence of (turbulent) hydrodynamic stresses induces droplets breakup and coalescence, influencing the micro-scale morphology of the emulsion that, in turn, influences the way these emulsions flow. We will discuss the production of jammed emulsions via large-scale turbulent stirring; furthermore, we will discuss the flowing of stabilised emulsions for different volume fractions. Let aside the many fascinating scientific challenges, the flow of complex fluids is relevant to several industrial processes, including the production of foods and cosmetics.