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Faced with the growing challenge of protecting the health of urban populations, the offer of fixed or mobile pollution control systems, capable of reducing pollutants but also greenhouse gases on a territory, is growing. The current offer of air pollution collection systems is very diversified: foam-based filtering bench, algae-based Morris column, air filter column, vegetated bus shelters, ...

There is also a range of mobile systems mounted on captive vehicles in urban areas (buses, garbage trucks, etc.), based on the principle of mechanical filtration using non-woven fibres. This mechanical filtration system has a limited life span and must be changed regularly (1 or 2 years). This change of products generates waste which is to date mainly recovered from an energy point of view, often by incineration.

The central idea of the thesis is to develop a pollution control system that can be embedded on a vehicle, whose life span is extended, the target being to avoid any change during the life of the vehicle.

The research question of the present thesis is therefore the following: what are the mechanisms of transport, deposition and trapping of particles in weakly turbulent flows?

The development objective will be to take advantage of the understanding of the phenomena in order to propose a depollution system that can be adapted to an automotive vehicle, i.e. by respecting the automotive specifications and applying its limiting criteria, the architectural and aerodynamic constraints specific to the automotive industry, and by including considerations related to the entire life cycle in order to minimize the environmental impact of the system.

The scientific challenges are of several kinds:

• From a physical point of view, it will be necessary to understand and model the impact of turbulent diffusion on the transport and deposition of particles, depending on their size and the nature of the carrier flow;
•  From a more mechanical point of view, it will be necessary to study the effects of the turbulent structures generated on the deposit;
• Finally, from a physico-chemical point of view, it will be necessary to understand how to ensure the trapping of particles on the collection surface (study and influence of the material) under the conditions of use of the vehicle (speed, aerodynamics, atmospheric conditions (humidity, ...) and nature of the particles (solid body and aerosol droplets).