Direct numerical simulation of monodisperse fluid-particle flows : methodology, validation, and application to fixed and fluidized beds
(2022)
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- Abstract
- Flows involving the transport of a dispersed solid phase by a carrier fluid are encountered in many environmental phenomena and industrial applications. Fluidized beds are now used in a wide variety of processes in the petrochemical and pharmaceutical sectors, in biomass conversion or in the food industry, among others. Those systems are characterized by a very large range of length and time scales. At the smallest scale, particle-resolved direct numerical simulation (PR-DNS) is a first-principles based approach, providing the complete details of the flow. With growing computational resources, PR-DNS has become a tool of choice to develop closures for the mass, momentum and energy transfer terms that need to be modeled in the large-scale Euler-Lagrange and Euler-Euler approaches. In this thesis, we first develop and validate a direct-forcing immersed boundary method to perform particle-resolved simulations of two- and three-dimensional fluid-particle flows. The method is then used to quantify the interfacial momentum and heat transfer terms in the flow past random particle arrays. While current drag laws only provide the mean value of the fluid-particle force, we propose a microstructure-based model to estimate the distribution of the force using a few quantities characterizing the local organization of the solid phase. The inhomogeneity of the thermal problem and the impact of thermal saturation on the distribution of the fluid-particle heat flux are also discussed. Finally, we perform a detailed comparison of the dynamics of small-scale fluidized beds in different regimes. In liquid fluidization, a homogeneous suspension is observed, owing to the small inertia of the particles. In gas fluidization, the higher inertia of the solid particles leads to the emergence of heterogeneities in the bed (bubbles and clusters) and to strong oscillatory motions. The impact of particle agitation on the fluid-particle force and fluid-particle heat flux is studied, as well as the influence of various physical and numerical parameters on the bed dynamics.
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Citations
Hardy, B. (2022). Direct numerical simulation of monodisperse fluid-particle flows : methodology, validation, and application to fixed and fluidized beds.