Federico Toschi, Ph.D.

a research website on fluid dynamics

Category: ph.d. (page 2 of 2)

Riccardo Scatamacchia

Extreme Events in the Dispersions of Two Neighboring Particles Under the Influence of Fluid Turbulence

Phys. Rev. Lett. 109, 144501 – Published 5 October 2012
R. Scatamacchia, L. Biferale, and F. Toschi



We present a numerical study of two-particle dispersion from point sources in three-dimensional incompressible homogeneous and isotropic turbulence at Reynolds number Re300. Tracer particles are emitted in bunches from localized sources smaller than the Kolmogorov scale. We report the first quantitative evidence, supported by an unprecedented statistics, of the deviations of relative dispersion from Richardson’s picture. Deviations are due to extreme events of pairs separating much faster than average, and of pairs remaining close for long time. The two classes of events are the fingerprints of complete different physics, the former dominated by inertial subrange and large-scale fluctuations, and the latter by dissipation subrange. A comparison of the relative separation in surrogate white-in-time velocity field, with correct viscous-, inertial-, and integral-scale properties, allows us to assess the importance of temporal correlations along tracer trajectories.

Michel van Hinsberg

Francesca Tesser


Population dynamics under flow


Simulations and experiments on populations of organisms living in aquatic environments and growing under flow conditions.


Ocean, rivers and lakes are natural environments for many living organisms. In these ecosystems they reproduce, compete for food, swim and die. The presence of a flow can have a strong effect on their dynamics both at individual and population scales. The dynamics of these systems are complicated because both transport and growth play a role. We are mainly interested in a population of individuals expanding in new territories and how the propagation speed is changed by the flow. Another question is how different species compete in such environments and, for example, how the extinction probability depends on the fluid dynamics. Population dynamics can be studied with numerical models but also experiments are performed with bacteria inside microfluidic devices. Bacteria are injected in micro-channels and observed for many days using microscopy equipment. We investigate how they colonize the channels and the way the colony propagates both upstream and downstream under flow. In order to measure these phenomena, the bacteria are modified and made fluorescent. It is possible to modify them in various ways so that they can be detected using different optical filters since they emit different colors. In this way also the competition between different growing species can be measured in space and time.

Florian Janoschek


Alessandro Corbetta

I work on crowd flow modelling.

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