Development of Immersed Boundary-Phase Field-Lattice Boltzmann Method for Solid Multiphase Flow Interactions

Ph.DDOCTOR OF PHILOSOPH

Particle interaction with binary-fluid interfaces in the presence of wetting effects

In this paper, we present an Eulerian-Lagrangian methodology to simulate the interaction between a fluid-fluid interface and a solid particle in the presence of wetting effects. The target physical problem is represented by ternary phase systems in which a solid phase and a drop phase interact inside an incompressible Newtonian carrier fluid. The methodology is based on an Eulerian-Lagrangian approach that allows for the numerical solution of the Continuity and Navier-Stokes equations by using a pseudo-spectral method, whereas the drop phase is modelled by the Phase Field Method, in which a smooth transition layer represented by an hyperbolic function is considered both across the solid-fluid interface and across the drop-fluid interface. Finally, the solid phase is described in the form of a virtual force using the Direct Forcing Immersed Boundary approach. The properties of the immersed solid phase (including wetting effects), the deformability of the drops and the characteristics of the carrier fluid flow are the main controlling parameters. To simulate a ternary phase system, the solid phase is coupled to the binary-fluid phase by introducing a single well potential in the free-energy density functional, which can also control the solid surface wetting property. The capabilities of the methodology are proven by examining first 2D and 3D validation cases in which a solid particle is settling in a quiescent fluid. Then, the interaction of solid particles with a binary-fluid interface and the effects of surface wetting on the submergence of a quasi-buoyant body are discussed. Finally, the equilibrium configuration for a solid particle interacting with an equally-sized drop at different contact angles and the relative rotation of two solid particles bridged by a drop are examined in the case the interaction is induced by shear fluid flow deformations on the drop interface

Lattice Boltzmann methods for multiphase flow and phase-change heat transfer

Over the past few decades, tremendous progress has been made in the development of particle-based discrete simulation methods versus the conventional continuum-based methods. In particular, the lattice Boltzmann (LB) method has evolved from a theoretical novelty to a ubiquitous, versatile and powerful computational methodology for both fundamental research and engineering applications. It is a kinetic-based mesoscopic approach that bridges the microscales and macroscales, which offers distinctive advantages in simulation fidelity and computational efficiency. Applications of the LB method are now found in a wide range of disciplines including physics, chemistry, materials, biomedicine and various branches of engineering. The present work provides a comprehensive review of the LB method for thermofluids and energy applications, focusing on multiphase flows, thermal flows and thermal multiphase flows with phase change. The review first covers the theoretical framework of the LB method, revealing certain inconsistencies and defects as well as common features of multiphase and thermal LB models. Recent developments in improving the thermodynamic and hydrodynamic consistency, reducing spurious currents, enhancing the numerical stability, etc., are highlighted. These efforts have put the LB method on a firmer theoretical foundation with enhanced LB models that can achieve larger liquid-gas density ratio, higher Reynolds number and flexible surface tension. Examples of applications are provided in fuel cells and batteries, droplet collision, boiling heat transfer and evaporation, and energy storage. Finally, further developments and future prospect of the LB method are outlined for thermofluids and energy applications

Fluid-Structure Interaction with the Entropic Lattice Boltzmann Method

We propose a novel fluid-structure interaction (FSI) scheme using the entropic multi-relaxation time lattice Boltzmann (KBC) model for the fluid domain in combination with a nonlinear finite element solver for the structural part. We show validity of the proposed scheme for various challenging set-ups by comparison to literature data. Beyond validation, we extend the KBC model to multiphase flows and couple it with FEM solver. Robustness and viability of the entropic multi-relaxation time model for complex FSI applications is shown by simulations of droplet impact on elastic superhydrophobic surfaces

IBM-LBM modelling of two-phase flow in porous media

The phenomena of Two-Phase Flow with large density ratio (about 1000:1) in porous media occurs in many environmental and industrial processes. This thesis aims to develop a numerical tool to simulate the Two-Phase Flow along curved solid boundaries with Lattice Boltzmann (LB) method. In addition, a modified Ghost Fluid Immersed Boundary (GFIB) model is proposed to capture the local interaction behaviour among fluids and curved boundaries. The code is first checked with the droplet test, capillary rise test, capillary bridge test and contact line dynamic test and all cases resulted in less than 5.0% error in comparison with the analytical solutions. Then it is further verified with capillary rise in porous media and the numerical pressure satisfies the theoretical one with 12.7% error. In addition, the parameter studies are conducted to gauge the influence of four main parameters in the model, including the interface thickness, the mobility, the domain size and the grid resolution with good results. As a result, the new code with the LB-GFIB model can provide an alternative way to study the complex process of Two-Phase Flow in the porous media

Review of Boundary Conditions and Investigation Towards the Development of a Growth Model: a Lattice Boltzmann Method Approach

El mètode de Lattice Boltzmann (LBM) es una tècnica computacional de simulació dinàmica de fluids que esta guanyant popularitat degut a les seves propietats inherents: pot treballar amb geometries complexes amb relativa facilitat, es fàcil de implementar computacionalment i pot ser utilitzat de forma efectiva amb eines de alta paralel·lització computacional. Tot i això el mètode encara no està totalment establert en la comunitat cientifica degut a la seva relativa primerenca aparició. Un conegut tòpic que està sota investigació activa és el desenvolupament de condicions de frontera efectives, especialment les no-reflexives. Podem trobar a la literatura diverses propostes de condicions de frontera no-reflexives per LBM. Tot i això, no hi ha massa investigació empresa sobre el impacte físic de utilitzar una condició de frontera reflexiva o no-reflexiva més enllà dels tests de condició de frontera. Per altra banda, el LBM també és capaç de recuperar la equació de transport de advecció-difusió utilitzant un escalar passiu. L'estudi de les plaquetes en la sang és un estudi molt actiu, i una de les tècniques utilitzades en LBM per modelitzar-ne el seu transport es a través de un escalar passiu. Les plaquetes son una peça clau en la coagulacio, que pot arribar a taponar una artèria quan la coagulació passa en una arteria amb arterioesclerosis severa. Les plaquetes també experimenten un moviment lateral cap a les parets, anomenada marginació, que augmenta de forma natural la seva capacitat de coagulació. La memòria de la tesi consisteix en dues parts distingides. Primerament, es presenten els resultats d'un estudi paramètric per analitzar el impacte físic de les reflexions artificials que es produeixen en un flux que passa per un obstacle dins d'un canal. En segon lloc, es desenvolupa un model de transport per a les plaquetes basat en la tècnica de la doble funció de distribució en LBM, es reprodueix el procés de la marginació i es prepara un grup de eines per a desenvolupar un model de creixement que pugui reproduir un episodi de trombosis en una artèria coronaria.l método lattice Boltzmann (LBM) es una técnica de computación dinámica de fluidos (CFD) que está ganando popularidad rápidamente debido a sus inherentes propiedades: trata formas geometricas con relativa facilidad, es computacionalmente fácil de implementar y se puede usar con herramientas de paralelización de forma eficaz. No obstante, este método no está enteramente establecido en la comunidad científica debido a su relativa temprana aparición. Un tema común que aún se encuentra en investigación activa es el estudio y desarrollo de condiciones de frontera efectivas, en especial las no-reflexivas. Se puede encontrat en la literatura varias propuestas de condiciones de frontera no-reflexivas, pero no hay mucha investigación hecha sobre el impacto físico que se genera al condiciones de frontera reflexivas o no-reflexivas mas allá de los test para las condiciones de frontera. Por otra parte, el método de lattice Boltzmann también puede desarrollar simulaciones basadas en la equación de advección-diffusion usando un escalar pasivo. Una temática muy activa que considera esta técnica es el transporte de las plaquetas en la sangre. Ellas son la clave del proceso de coagulación, pueden llegar a taponar una arteria que tenga arterioesclerosis severa. Adicionalmente, las plaquetas presentan un desplazamento lateral espontáneo, llamado marginación, y generan un exceso de concentración de plaquetas cerca de las paredes de la arteria. El reporte de la tesis consiste en dos partes diferenciadas. Primero se presenta un estudio parametrico en el cual se analiza y caracteriza el impacto the las reflexiones producidas en un flujo en un canal con un obstáculo en el medio. Después, se desarrolla un modelo de plaquetas basado en la doble dfunción de distribución y reproducimos el efecto de marginación de las plaquetas. Adicionalmente preparamos un conjunto de herramientas computacionals para desarrollar un modelo de crecimiento que se asemeje a un episodio de trombosis en una arteria coronaria.The lattice Boltzmann method (LBM) is a computational fluid dynamics technique that is rapidly earning popularity due to its inherent properties: it deals with complex geometries with relative ease, it is computationally easy to implement and it can be effectively used with massive parallel computing tools. However, the method is still not entirely established in the scientific community due to its relatively early appearance. One known topic that is still under active research are the study and development of effective boundary conditions, specially non-reflecting ones. We can find on the literature several proposals of non-reflective boundary conditions for LBM. However, there is not much conducted research about the physical impact of using a reflective or a non-reflective approach on a simulation beyond the boundary tests. On the other hand, the LBM is also capable to able to hold the advection-diffusion transport equation by means of a passive scalar. One very active topic is the study of the blood platelet transport. Platelets are the cornerstone of the coagulation and this latter phenomenon can occlude an artery when platelets are activated in an atherosclerotic artery, which is called thrombosis. Platelets also experiment a spontaneous migration, called margination, to the walls that naturally enhance their performance. The thesis report consists on two distinct parts. Firstly, we present the results of a parametric study to analyze the physical impact of the spurious reflections that occur on a flow past a square obstacle in a confined channel. Secondly, we develop a transport model for platelets in the LBM based on the double distribution technique and we reproduce the margination of platelets and we prepare a set of tools to develop a growth model to resemble a thrombosis event in a coronary artery

Challenges in imaging and predictive modeling of rhizosphere processes

Background Plant-soil interaction is central to human food production and ecosystem function. Thus, it is essential to not only understand, but also to develop predictive mathematical models which can be used to assess how climate and soil management practices will affect these interactions. Scope In this paper we review the current developments in structural and chemical imaging of rhizosphere processes within the context of multiscale mathematical image based modeling. We outline areas that need more research and areas which would benefit from more detailed understanding. Conclusions We conclude that the combination of structural and chemical imaging with modeling is an incredibly powerful tool which is fundamental for understanding how plant roots interact with soil. We emphasize the need for more researchers to be attracted to this area that is so fertile for future discoveries. Finally, model building must go hand in hand with experiments. In particular, there is a real need to integrate rhizosphere structural and chemical imaging with modeling for better understanding of the rhizosphere processes leading to models which explicitly account for pore scale processes