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Turbulent transport and dispersion

Many natural and industrial processes, ranging from combustion engines to planet formation involve the transport of material inclusions (dust, powders, sediments, bubbles, droplets) by a turbulent fluid. Accurately quantifying the positions, attributes and effects of such particles is essential to investigate these systems. Current approaches oversimplify small-scale physics and poorly capture certain effects, including concentration fluctuations, variations in size and shape, agglomeration and complex interactions with fluid and walls. Improving macroscopic models remains a real challenge.

Fluctuations in turbulent transport

Models used to predict air quality are designed to estimate average concentrations and do not resolve small-scale turbulent fluctuations. They give a good handle on long-term averages and can be successfully used to determine health hazards due to a long exposure downstream a pollutant source. However, they cannot be use to describe risks associated to strong, local, instantaneous fluctuations. In this scope, tools borrowed from statistical physics and large-deviation theory can be used to predict violent and intermittent events.

Dynamics of finite-size, complex particles

Its is often assumed that transported particles are spherical and small enough, so that their dynamics only involve the fluid velocity at their position. This provides a useful framework to describe their dynamics. However, particles often have finite sizes, complex shapes and rotate. Their dynamics then implies the local structure of the flow and modeling requires information from different turbulent scales.

Fibers and deformable particles

Long, semiflexible particles transported by a turbulent flow can bend depending on the shear they experience along their length. In the presence of inhomogeneities, this leads to their concentration in specific regions of the flow.

Local and distant interactions between particles

Often, suspended particles are too dense to ignore their mutual interactions. It is then necessary to follow precisely their size distribution by estimating for example the rates at which they agglomerate. Describing the evolution of the particle size must therefore be based on an efficient coupling between population dynamics and unsteady turbulence models.

Transfers to a complex environment

Designing practical modeling tools requires precise estimates either for the feedback of the particles onto the flow or for their deposition on walls of the flow. This last question is particularly important for the design of efficient filtration systems or for the prediction of fouling which could obstruct a confined flow.