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Rhéologie et propriétés de vidange de milieux granulaires modèles : application à l’écoulement en silo

Abstract : The discharge of grain in a silo is a common application in industry, but this typical granular flow is still not fully understood. Without a real fundamental understanding, the optimization of this application is done by empirical means, for example by applying vibrations to improve the discharge. Understanding the behaviour of this flow, and in particular the link between the apparent flow rate and the particle reorganization dynamics, would therefore allow a theoretical breakthrough and would open up practical ways of optimizing these flows in an industrial configuration. In this thesis, we study the discharge of model granular matter (monodisperse spherical beads) in a quasi-2D silo under the influence of mechanical vibrations. Experimental measurements and discrete element simulations (DEM) are performed to determine the effect of the geometry, particle properties and vibration characteristics. We evidence that vibrations make appear two distinct regimes, governed by the Froude number Fr and the relative frequency Ω of the vibrations. In the first regime, a decreased flow rate is observed when increasing the vibration intensity. This behavior is explained by the setting in motion, due to the vibration, of areas previously at rest and a higher energy dissipation. In the second regime, an increased flow rate is observed when increasing the vibration intensity. We find this behavior comes from the intermittent nature of the flow, with bursts of flow rate created by the propagation of shock waves all along the silo. As a first step, we propose for each regime an empirical law for the flow rate depending on the different parameters. Then, we studied the flow at the local scale in order to relate the apparent flow rate to local particle dynamics through flow rheology.
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Submitted on : Friday, February 5, 2021 - 11:34:55 AM
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Arthur Pascot. Rhéologie et propriétés de vidange de milieux granulaires modèles : application à l’écoulement en silo. Dynamique des Fluides [physics.flu-dyn]. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0156⟩. ⟨tel-03132596⟩

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