Presentation of the Scientific Breakthrough Project "TurBullet"

In spite of its apparent simplicity, the problem of spherical particles settling in a fluid hides a whole hierarchy of rich intricate phenomena, some of which are still shrouded in mystery. The question is by no means just rhetorical, as it impacts numerous real situations, such as the atmospheric dispersion of pollutants, dynamics of dust in proto-planetary accretion disks, transport of grains in geophysical flows and sprays in industrial processes to cite just a few examples. Unveiling the fundamental mechanisms of drifting particles (the case of settling corresponding to gravity induced drift) in turbulence has become a crucial issue to improve our capacity to accurately model and predict such particle-laden flows.
 

 

As an example, we can mention astrophysical applications. Major contemporary observation instruments (ALMA, Herschel, SPHERE, JWST) scrutinise the sky at millimetric wavelength and therefore detect indeed the light scattered by dust in space (the figure on the left shows for instance the first observation of dust in a proto-planetary system, made by the ALMA observatory in 2014). Understanding its dynamics and its coupling with the surrounding gas has become a major challenge to interpret the observations. Besides, it is also from this coupling that planets emerge form the dust. In the geophysical context, erosion processes rely heavily on particles-flow interactions: eolian transport of sand grains, rainfalls, landslides, river transport, sediment deposition. Within the lithosphere, partial melting, crystallization and transport of grains in magma chambers and ducts contribute to the chemical differenciation of the crust. In the deep interior of the Earth, a possible scenario of the secular cooling of the liquid iron core involves the settling of solid iron grains leading to the formation and growth of the solid inner core.