讲座题目：Lagrangian studies in turbulent flows: from inertial to active particles
讲座人： Prof. Enrico Calzavarini Université de Lille, Laboratoire de Mécanique de Lille（法国里尔大学）
摘要：Particle-laden turbulent flows are widespread phenomena both in natural sciences and in industrial applications. We encounter particle seeded turbulence in the description of pollutant dispersion in the atmosphere, in cloud physics of rain formation, in marine biology for the description of ocean plankton colonies, in astrophysics for planet formation and finally in techno- logical applications such as chemical and mechanical industrial processes aimed at controlling mixing, energy dissipation or sedimentation. The advancement of the understanding of statisti- cal properties of particles in turbulent flows has a pivotal role in each of these areas and a great amount of work has been devoted to better understand them through experiments, numerical simulations and theoretical studies.
In this talk, I will first review recent findings on the properties of small inertial particles and bubbles in a flow. The focus will be on the properties of acceleration, a quantity that is closely linked to the hydrodynamic forces acting on the particles and that allows for the most direct comparison between numerical studies and experiments. In particular we will see to what extent a buoyant sub-Kolmogorov scale inertial particle can be considered a faithful proxy of fluid tracer acceleration .
Due to the sinking/rising velocity induced by buoyancy, in some respect small particles and bubbles in turbulence can be assimilated to particles cruising in a flow. This provides a link with a second series of studies where self-propelled point-like probes drifting in a flow are consid- ered . The recorded time-series of fluid velocity and of the intensity of a scalar concentration along these moving probes represents the simplest realisation of a transect measurement in a fluid environment. I will show how transect measurements display a non trivial combination of Lagrangian and Eulerian phenomenology and how a transition from one regime to the other occurs at increasing the propulsion velocity.
The model of drifting particles can also be extended to include the occurrence of particle reorientation by the surrounding fluid flow. In its simple realisation small for-aft symmetric particles are oriented by the instantaneous local fluid gradients at the particle position. However, even in this simple case the resulting tumbling dynamics in a turbulent flow is far from being trivial and this is even more complex when particle propulsion and orientation combines with each other.
Finally, I will illustrate some applications of the modelisation discussed above to the study of the motility of swimming scalar-tactic bacteria and plankton in turbulent flows.
专家简介: Enrico Calzavarini is assistant professor at University of Lille and researcher in the Laboratory of Mechanics of Lille, France.
He received his PhD in 2005 from University of Ferrara, Italy and worked as a postdoc from 2005 to 2008 at the University of Twente in the Netherlands and from 2008 and 2010 at the E ́cole Normale Suprieure de Lyon, France.
His research interests focus on numerical investigation of turbulent flows, on developed thermal convection, on Lagrangian properties of fluid turbulence and on the dynamics of particles in turbulence. His research work has been published in PRL, PRE and JFM.