Research Projects

Granular materials, the second most handled material after water, show very complex behaviour, which is critically dependent upon particle properties, system constraints and external loading. Depending upon boundary conditions and the manner in which they are forced, these materials behave as a solid, a liquid or a gas. Modelling their mechanical response is therefore a challenge. It is however a challenge that must be met in order to provide realistic, physics-based interpretation and prediction of how a system consisting of grains behaves or will behave. Such questions find crucial applications in multiple fields: geophysics (e.g. triggering and propagation of avalanches, debris flow, surface transport of lunar or martian sand), industry (e.g. food and drugs production, aggregate processing, silicon processing in electronic industry), terramechanics (e.g. how to efficiently traverse sandy deserts, spacecraft landing). The current ARG project aims at improving the understanding and modelling of granular flow dynamics by means of theoretical and numerical investigations with a focus on industrial flows. A detailed analysis of the grain-grain (particle-particle) and fluid-grain (fluid-particle) interactions, in a simplified contest represented by particle-fluid flow through a vertical pipe, will be performed. Subsequently, the project will focus on real industrial processes. The theoretical model will be based on the Kinetic Theory for Granular Flows (KT) for the particle phase and Navier-Stokes equation for the fluid phase. KT has been extremely successful in dry granular flows (without fluid), however, it has limited applications to vertical particle-fluid flows thus far. We will propose improvements to this physics based approach, especially for the case of dense flows, inelastic collisions, and fluid-grain interactions. The theoretical predictions will be validated through comparison with numerical simulations and laboratory experimental results (from literature and via collaboration), and will serve as a confirmation for the ability of these physics based models to properly predict the behavior of real scale granular flows. The project has a double objective: (1) it will contribute to the fundamental research in the granular physics field, and (2) it will enable use of KT based models, along with CFD-DEM simulations, for granular flows, leading to an improved efficiency in several industrial processes involving particle-fluid interactions. The proposed research will: 1. Perform the kinetic theory and CFD-DEM based analysis for fluid-particle flow through a vertical pipe for the entire range of particle volume fraction. 2. Refine the turbulent viscosity and particle-drag models to ensure that the KT formulation is valid for the entire range of particle volume fraction and different boundary types. 3. Consider different fluid-particle combinations by changing the material density ratio between solid and fluid and by varying different input parameters within the same KT based framework. 4. Employ the knowledge for a few industrial processes to optimize the design and operating conditions. The key questions to be addressed in the project are: 1. How do grain-grain and fluid-grain interactions influence the flow of granular matter? 2. What are the modifications in the drag/viscosities of the particle and fluid phases in the regimes outside dense and dilute particle concentrations? 3. What is the role of boundary conditions in the grain-fluid flows?