The Euler and Navier-Stokes-Fourier equations will be directly expressed as distribution evolution equations, where a new and proper continuum prescription will be derived. These equations of motion will be numerically solved with the development of a new and unique finite element formulation. Out of this framework, the 7D phasetime element has been born. To provide optimal stability, a new quantization procedure is established based on the principles of quantum theory. The entirety of this framework has been coined the "quantized velocity finite element method" (QVFEM). The work performed herein lays the foundational development of what is hoped to become a new paradigm shift in computational fluid dynamics. / Doctor of Philosophy / To model any of the four fundamental states of matter, for practical engineering applications, we must first recognize the complexity of such states. In consequence, a new and novel approach is presented on how to numerically simulate the dynamics of a gas using both the Euler and Navier-Stokes-Fourier equations of continuum mechanics and thermodynamics. In contrast to direct numerical simulation, a statistical mechanical prescription will be given where the equations of motion will be quantized using methods taken from the study of quantum mechanics. This newly developed discretization of the phase space and time, or phasetime, provides optimal stability for compressible flow simulations. From the newly proposed framework, the 7D phasetime element has been born.

Contamination is becoming an important problem in great metropolitan areas. A large portion of the contaminants is emitted by the vehicle fleet. At European level, as well as in other economical areas, the regulation is becoming more and more restrictive. Euro regulations are the best example of this tendency. Specially important are the emissions of nitrogen oxide (NOx) and Particle Matter (PM). Two different strategies exist to reduce the emission of pollutants. One of them is trying to avoid their creation. Modifying the combustion process by means of different fuel injection laws or controlling the air regeneration are the typical methods. The second set of strategies is focused on the contaminant elimination. The NOx are reduced by means of catalysis and/or reducing atmosphere, usually created by injection of urea. The particle matter is eliminated using filters. This thesis is focused in this matter. Most of the strategies to reduce the emission of contaminants penalise fuel consumption. The particle filter is not an exception. Its installation, located in the exhaust duct, restricts the pass of the air. It increases the pressure along the whole exhaust line before the filter reducing the performance. Optimising the filter is then an important task. The efficiency of the filter has to be good enough to obey the contaminant normative. At the same time the pressure drop has to be as low as possible to optimise fuel consumption and performance. The objective of the thesis is to find the relation between the micro-structure and the macroscopic properties. With this knowledge the optimisation of the micro-structure is possible. The micro-structure of the filter mimics acicular mullite. It is created by procedural generation using random parameters. The relation between micro-structure and the macroscopic properties such as porosity and permeability are studied in detail. The flow field is solved using LabMoTer, a software developed during this thesis. The formulation is based on Lattice Botlzmann Methods, a new approach to simulate fluid dynamics. In addition, Walberla framework is used to solve the flow field too. This tool has been developed by Friedrich Alexander University of Erlangen Nürnberg. The second part of the thesis is focused on the particles immersed into the fluid. The properties of the particles are given as a function of the aerodynamic diameter. This is enough for macroscopic approximations. However, the discretization of the porous media has the same order of magnitude than the particle size. Consequently realistic geometry is necessary. Diesel particles are aggregates of spheres. A simulation tool is developed to create these aggregated using ballistic collision. The results are analysed in detail. The second step is to characterise their aerodynamic properties. Due to the small size of the particles, with the same order of magnitude than the separation between molecules of air, the fluid can not be approximated as a continuous medium. A new approach is needed. Direct Simulation Monte Carlo is the appropriate tool. A solver based on this formulation is developed. Unfortunately complex geometries could not be implemented on time. The thesis has been fruitful in several aspects. A new model based on procedural generation has been developed to create a micro-structure which mimics acicular mullite. A new CFD solver based on Lattice Boltzmann Methods, LabMoTer, has been implemented and validated. At the same time it is proposed a technique to optimized setup. Ballistic agglomeration process is studied in detail thanks to a new simulator developed ad hoc for this task. The results are studied in detail to find correlation between properties and the evolution in time. Uncertainty Quantification is used to include the Uncertainty in the models. A new Direct Simulation Monte Carlo solver has been developed and validated to calculate rarefied flow. / La contaminación se está volviendo un gran problema para las grandes áreas metropolitanas, en gran parte debido al tráfico. A nivel europeo, al igual que en otras áreas, la regulación es cada vez más restrictiva. Una buena prueba de ello es la normativa Euro de la Unión Europea. Especialmente importantes son las emisiones de óxidos de nitrógeno (NOx) y partículas (PM). La reducción de contaminantes se puede abordar desde dos estrategias distintas. La primera es la prevención. Modificar el proceso de combustión a través de las leyes de inyección o controlar la renovación de la carda son los métodos más comunes. La segunda estrategia es la eliminación. Se puede reducir los NOx mediante catálisis o atmósfera reductora y las partículas mediante la instalación de un filtro en el conducto de escape. La presente tesis se centra en el estudio de éste último. La mayoría de as estrategias para la reducción de emisiones penalizan el consumo. El filtro de partículas no es una excepción. Restringe el paso de aire. Como consecuencia la presión se incrementa a lo largo de toda la línea reduciendo las prestaciones del motor. La optimización del filtro es de vital importancia. Tiene que mantener su eficacia a la par que que se minimiza la caída de presión y con ella el consumo de combustible. El objetivo de la tesis es encontrar la relación entre la miscroestructura y las propiedades macroscópicas del filtro. Las conclusiones del estudio podrán utilizarse para optimizar la microestructura. La microestructura elegida imita los filtros de mulita acicular. Se genera por ordenador mediante generación procedimental utilizando parámetros aleatorios. Gracias a ello se puede estudiar la relación que existe entre la microestructura y las propiedades macroscópicas como la porosidad y la permeabilidad. El campo fluido se resuelve con LabMoTer, un software desarrollado en esta tesis. Está basado en Lattice Boltzmann, una nueva aproximación para simular fluidos. Además también se ha utilizado el framework Walberla desarrollado por la universidad Friedrich Alexander de Erlangen Nürnberg. La segunda parte de la tesis se centra en las partículas suspendidas en el fluido. Sus propiedades vienen dadas en función del diámetro aerodinámico. Es una buena aproximación desde un punto de vista macroscópico. Sin embargo éste no es el caso. El tamaño de la discretización requerida para calcular el medio poroso es similar al tamaño de las partículas. En consecuencia se necesita simular geometrías realistas. Las partículas Diesel son agregados de esferas. El proceso de aglomeración se ha simulado mediante colisión balística. Los resultados se han analizado con detalle. El segundo paso es la caracterización aerodinámica de los aglomerados. Debido a que el tamaño de las partículas precursoras es similar a la distancia entre moléculas el fluido no puede ser considerado un medio continuo. Se necesita una nueva aproximación. La herramienta apropiada es la Simulación Directa Monte Carlo (DSMC). Por ello se ha desarrollado un software basado en esta formulación. Desafortunadamente no ha habido tiempo suficiente como para implementar condiciones de contorno sobre geometrías complejas. La tesis ha sido fructífera en múltiples aspectos. Se ha desarrollado un modelo basado en generación procedimental capaz de crear una microestructura que aproxime mulita acicular. Se ha implementado y validado un nuevo solver CFD, LabMoTer. Además se ha planteado una técnica que optimiza la preparación del cálculo. El proceso de aglomeración se ha estudiado en detalle gracias a un nuevo simulador desarrollado ad hoc para esta tarea. Mediante el análisis estadístico de los resultados se han planteado modelos que reproducen la población de partículas y su evolución con el tiempo. Técnicas de Cuantificación de Incertidumbre se han empleado para modelar la dispersión de datos. Por último, un simulador basado / La contaminació s'està tornant un gran problema per a les grans àrees metropolitanes, en gran part degut al tràfic. A nivell europeu, a l'igual que en atres àrees, la regulació és cada volta més restrictiva. Una bona prova d'això és la normativa Euro de l'Unió Europea. Especialment importants són les emissions d'òxits de nitrogen (NOX) i partícules (PM). La reducció de contaminants se pot abordar des de dos estratègies distintes. La primera és la prevenció. Modificar el procés de combustió a través de les lleis d'inyecció o controlar la renovació de la càrrega són els mètodos més comuns. La segona estratègia és l'eliminació. Se pot reduir els NOX mediant catàlisis o atmòsfera reductora i les partícules mediant l'instalació d'un filtre en el vas d'escap. La present tesis se centra en l'estudi d'este últim. La majoria de les estratègies per a la reducció d'emissions penalisen el consum. El filtre de partícules no és una excepció. Restringix el pas d'aire. Com a conseqüència la pressió s'incrementa a lo llarc de tota la llínea reduint les prestacions del motor. L'optimisació del filtre és de vital importància. Ha de mantindre la seua eficàcia a la par que que es minimisa la caiguda de pressió i en ella el consum de combustible. L'objectiu de la tesis és trobar la relació entre la microescritura i les propietats macroscòpiques del filtre. Les conclusions de l'estudi podran utilisar-se per a optimisar la microestructura. La microestructura elegida imita els filtres de mulita acicular. Se genera per ordenador mediant generació procedimental utilisant paràmetros aleatoris. Gràcies ad això es pot estudiar la relació que existix entre la microestructura i les propietats macroscòpiques com la porositat i la permeabilitat. El camp fluït se resol en LabMoTer, un software desenrollat en esta tesis. Està basat en Lattice Boltzmann, una nova aproximació per a simular fluïts. Ademés també s'ha utilisat el framework Walberla, desentollat per l'Universitat Friedrich Alexander d'Erlangen Nürnberg. La segona part de la tesis se centra en les partícules suspeses en el fluït. Les seues propietats venen donades en funció del diàmetro aerodinàmic. És una bona aproximació des d'un punt de vista macroscòpic. No obstant este no és el cas. El tamany de la discretisació requerida per a calcular el mig porós és similar al tamany de les partícules. En conseqüència es necessita simular geometries realistes. Les partícules diésel són agregats d'esferes. El procés d'aglomeració s'ha simulat mediant colisió balística. Els resultats s'han analisat en detall. El segon pas és la caracterisació aerodinàmica dels aglomerats. Degut a que el tamany de les partícules precursores és similar a la distància entre molècules el fluït no pot ser considerat un mig continu. Se necessita una nova aproximació. La ferramenta apropiada és la Simulació Directa Monte Carlo (DSMC). Per això s'ha desenrollat un software basat en esta formulació. Malafortunadament no ha hagut temps suficient com per a implementar condicions de contorn sobre geometries complexes. La tesis ha segut fructífera en múltiples aspectes. S'ha desenrollat un model basat en generació procedimental capaç de crear una microestructura que aproxime mulita acicular. S'ha implementat i validat un nou solver CFD, LabMoTer. Ademés s'ha plantejat una tècnica que optimisa la preparació del càlcul. El procés d'aglomeració s'ha estudiat en detall gràcies a un nou simulador desenrollat ad hoc per ad esta tasca. Mediant l'anàlisis estadístic dels resultats s'han plantejat models que reproduixen la població de partícules i la seua evolució en el temps. Tècniques de Quantificació d'Incertea s'han empleat per a modelar la dispersió de senyes. Per últim, un simulador basat en DSMC s'ha desenrollat per a calcular fluïts rarificats. / García Galache, JP. (2017). Study of the flow field through the wall of a Diesel particulate filter using Lattice Boltzmann Methods [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90413

Most realistic fluid flow problems are characterised by high Reynolds numbers and complex boundaries. Over the last ten years, immersed boundary methods (IBM) that are able to cope with realistic geometries have been applied to Lattice- Boltzmann methods (LBM). These methods, however, have normally been applied to low Reynolds number problems. In the present work, an iterative direct forcing IBM has been successfully coupled with a multi-domain cascaded LBM in order to investigate viscous flows around rigid, moving and wilfully deformed boundaries at a wide range of Reynolds numbers. The iterative force-correction immersed boundary method of (Zhang et al., 2016) has been selected due to the improved accuracy of the computation, while the cascaded LB formulation is used due to its superior stability at high Reynolds numbers. The coupling is shown to improve both the stability and numerical accuracy of the solution. The resulting solver has been applied to viscous flow (up to a Reynolds number of 100000) passed a NACA-0012 airfoil at a 10 degree angle of attack. Good agreement with results obtained using a body-fitted Navier-Stokes solver has been obtained. At moving or deformable boundary applications, emphasis should be given on the influence of the internal mass on the computation of the aerodynamic forces, focusing on deforming boundary motions where the rigid body approximation is no longer valid. Both the rigid body and the internal Lagrangian points approximations are examined. The resulting solver has been applied to viscous flows around an in-line oscillating cylinder, a pitching foil, a plunging SD7003 airfoil and a plunging and flapping NACA-0014 airfoil. Good agreement with experimental results and other numerical schemes has been obtained. It is shown that the internal Lagrangian points approximation accurately captures the internal mass effects in linear and angular motions, as well as in deforming motions, at Reynolds numbers up to 4 • 104. Finally, an expanded higher-order immersed boundary method which addresses two major drawbacks of the conventional IBM will be presented. First, an expanded velocity profile scheme has been developed, in order to compensate for the discontinuities caused by the gradient of the velocity across the boundary. Second, a numerical method derived from the Navier-Stokes equations in order to correct the pressure distribution across the boundary has been examined. The resulting hybrid solver has been applied to viscous flows around stationary and oscillating cylinders and examined the hovering flight of elliptical wings at low Reynolds numbers. It is shown that the proposed scheme smoothly expands the velocity profile across the boundary and increases the accuracy of the immersed boundary method. In addition, the pressure correction algorithm correctly expands the pressure profile across the boundary leading to very accurate pressure coefficient values along the boundary surface. The proposed numerical schemes are shown to be very efficient in terms of computational cost. The majority of the presented results are obtained within a few hours of CPU time on a 2.8 GHz Intel Core i7 MacBook Pro computer with a 16GB memory.

<p>Lattice Boltzmann-based (LB) simulations are well suited to the simulation of fluid flows in complex structures encountered in chemical engineering like porous media or structured packing used in distillation and reactive distillation columns. These simulations require large amounts of memory (around 10 gigabytes) and would require very long execution times (around 2 years) if executed on a single powerful desktop computer.</p> <p>The execution of LB simulations in a distributed way (for example, using cluster computing) can decrease the execution time and reduces the memory requirements for each computer. Dynamic Heterogeneous Clusters (DHC) is a class of clusters involving computers inter-connected by a local area network; these computers are potentially unreliable and do not share the same architecture, operating system, computational power, etc. However, DHCs are easy to setup and extend, and are made of affordable computers.</p> <p>The design and development of a software system which organizes large scale DHCs in an efficient, scalable and robust way for implementing very large scale LB simulations is challenging. In order to avoid that some computers are overloaded and slow down the overall execution, the heterogeneity of computational power should be taken into account. In addition, the failure of one or several computers during the execution of a simulation should not prevent its completion.</p> <p>In the context of this thesis, a simulation tool called LaBoGrid was designed. It uses existing static load balancing tools and implements an original dynamic load balancing method in order to distribute the simulation in a way that minimizes its execution time. In addition, a distributed and scalable fault-tolerance mechanism based on the regular saving of simulation's state is proposed. Finally, LaBoGrid is based on a distributed master-slave model that is robust and potentially scalable.</p> <br/> <p>Les simulations basées sur les méthodes de Lattice Boltzmann sont bien adaptées aux simulations d'écoulements de fluides à l'intérieur de structures complexes rencontrées en génie chimique, telles que les milieux poreux ou les empilements structurés utilisés dans des colonnes de distillation et de distillation réactive. Elles requièrent toutefois de grandes quantités de mémoire (environ 10 gigaoctets). Par ailleurs, leur exécution sur un seul ordinateur de bureau puissant nécessiterait un temps très long (environ deux ans).</p> <p>Il est possible de réduire à la fois le temps d'exécution et la quantité de mémoire requise par ordinateur en exécutant les simulations LB de manière distribuée, par exemple en utilisant un cluster. Un Cluster Hétérogène Dynamique (CHD) est une classe de clusters impliquant des ordinateurs qui sont interconnectés au moyen d'un réseau local, qui ne sont pas nécessairement fiables et qui ne partagent pas la même architecture, le même système d'exploitation, la même puissance de calcul, etc. En revanche, les CHD sont faciles à installer, à étendre et peu coûteux.</p> <p>Concevoir et développer un logiciel capable de gérer des CHD à grande échelle de façon efficace, extensible et robuste et capable d'effectuer des simulations LB à très grande échelle constitue un défi. L'hétérogénéité de la puissance de calcul doit être prise en compte afin d'éviter que certains ordinateurs soient débordés et ralentissent le temps global d'exécution. En outre, une panne d'un ou de plusieurs ordinateurs pendant l'exécution d'une simulation ne devrait pas empêcher son achèvement.</p> <p>Dans le contexte de cette thèse, un outil de simulation appelé LaBoGrid a été conçu. LaBoGrid utilise des outils existants de répartition statique de la charge et implémente une méthode originale de répartition dynamique de la charge, ce qui lui permet de distribuer une simulation LB de manière à minimiser son temps d'exécution. De plus, un mécanisme distribué et extensible de tolérance aux pannes, fondé sur une sauvegarde régulière de l'état de simulation, est proposé. Enfin, LaBoGrid se base sur un modèle distribué de type « maître-esclaves » qui est robuste et potentiellement extensible.</p>

An understanding of the motion of soft capsules in microchannels is useful for a number applications. This knowledge can be used to develop devices to sort biological cells based on their size and stiffness. For example, cancer cells have a different stiffness from healthy cells and thus can be readily identified. Additionally, devices can be developed to detect flaws in synthetic particles. Using a 3D hybrid lattice Boltzmann and lattice spring method, the motion of rigid and soft capsules in a pressure-driven microfluidic flow was probed. The effect of inertial drift is evaluated in channels different Reynolds numbers. Other system parameters such as capsule elasticity and channel size are also varied to determine their effect. The equilibrium position of capsules in the channel is also obtained. The equilibrium position of rigid and soft capsules depends on the relative particle size. If the capsule is small, the equilibrium position is found to be closer to the channel wall. Conversely, for larger capsules, the equilibrium position is closer to the channel centerline. The capsule stiffness affects the magnitude of the cross-stream drift velocity. For a given Reynolds number, the equilibrium position of softer capsules is closer to the channel centerline. However, It is found that the equilibrium position of soft capsules is insensitive to the magnitude of the Reynolds number.

This thesis focuses on the lattice-Boltzmann method (LBM) and its ability to simulate immiscible two-phase flow. We introduce the main lattice-Boltzmann-based approaches for analyzing two-phase flow: the color-fluid model by Gunstensen, the interparticle-potential model by Shan and Chen, the free-energy model by Swift and Orlandini, and the mean-field model by He. The first objective is to assess the ability of these methods to maintain continuity at the interface of two fluids, especially when the two fluids have different viscosities or densities. Continuity issues have been mentioned in the literature but have never been quantified. This study presents a critical comparison of the four lattice-Boltzmann-based approaches for analyzing two-phase flow by analyzing the results of the two-phase Poiseuille flow for different viscosity ratios and density ratios. The second objective is to present the capability of the most recent version of the color-fluid model for simulating 3D flows. This model allows direct control over the surface tension at the interface. We demonstrate the ability of this model to simulate surface tension effects at the interface (Laplace bubble test), stratified two-phase flows Poiseuille two-phase flow), and bubble dynamics (the free rise of a bubble in a quiescent viscous fluid).

Helicopter performance is greatly influenced by its drag. Pylons, fuselage, landing gear, and especially the rotor hub of a helicopter experience large separated flow regions, even under steady level flight conditions the vehicle has been designed for, contributing to the helicopter drag. Several passive and active flow control concepts have been studied for reducing helicopter drag. While passive flow control methods reduce drag, they do so at one optimized design condition. Therefore, passive drag reduction methods may not work for helicopters that operate under widely varying flight conditions. Active flow control (AFC) methods overcome this disadvantage and consequently are widely being pursued. The present investigator has studied some of these AFC methods using computational fluid dynamics (CFD) techniques and has found synthetic (or pulsed) jets as one of the more effective drag reduction devices. Two bluff bodies, representative of helicopter components, have been studied and the mechanism behind drag reduction has been analyzed. It was found that the increase in momentum due to the jet, and a resultant reduction in the separated flow region, is the main reason for drag reduction in these configurations. In comparison with steady jets, synthetic jets were found to use less power for a greater drag reduction. The flow inside these synthetic jet devices is incompressible. It is computationally inefficient to use compressible flow solvers in incompressible regions. In such regions, using Lattice Boltzmann equations (LBE) is more suitable compared to solving the incompressible Navier-Stokes equations. The length scales close to the synthetic jet devices are very small. LBE may be used to better resolve these small length scale regions. However, using LBE throughout the whole domain would be computationally expensive since the grid spacing in the LBE solver has to be of the order of the mean free path. To address this need, a coupled Lattice Boltzmann-Navier-Stokes (LB-NS) methodology has been developed. The LBE solver has been successfully validated in a standalone manner for several benchmark cases. The solver has also been shown to be of second order accuracy. This LBE solver has been subsequently coupled with an existing Navier-Stokes (NS) solver. Validation of the coupled methodology has been done for analytical problems with known closed form solution. This LB-NS methodology is further used to simulate the flow past a cylinder where synthetic jet devices have been used to reduce drag. The LBE solver is used in the cavity of the synthetic jet nozzle while the NS solver is employed in the rest of the domain. The cylinder configuration was chosen to demonstrate drag reduction on helicopter hub shape geometries. Significant drag reduction is observed when synthetic jets are used, compared to the baseline no flow control case.

Defective or diseased native valves have been replaced by bileaflet mechanical heart valves (BMHVs) for many years. However, severe complications still exist, and thus blood damage that occurs in BMHV flows must be well understood. The aim of this research is to numerically study platelet damage that occurs in BMHV flows. The numerical suspension flow method combines lattice-Boltzmann fluid modeling with the external boundary force method. This method is validated as a general suspension flow solver, and then validated against experimental BMHV flow data. Blood damage is evaluated for a physiologic adult case of BMHV flow and then for BMHVs with pediatric sizing and flow conditions. Simulations reveal intricate, small-scale BMHV flow features, and the presence of turbulence in BMHV flow. The results suggest a shift from previous evaluations of instantaneous flow to the determination of long-term flow recirculation regions when assessing thromboembolic potential. Sharp geometries that may induce these recirculation regions should be avoided in device design. Simulations for predictive assessment of pediatric sized valves show increased platelet damage values for potential pediatric valves. However, damage values do not exceed platelet activation thresholds, and highly damaged platelets are found far from the valve. Thus, the increased damage associated with resized valves is not such that pediatric valve development should be hindered. This method can also be used as a generic tool for future evaluation of novel prosthetic devices or cardiovascular flow problems.

The characteristics of fibers suspensions depend on the properties of fibers, the suspending fluid, and fiber-fiber interactions. This thesis demonstrates the development and application of a novel coupled method (lattice Boltzmann and finite element methods) to investigate these relationships. Fibers are modeled as flexible rod particles which are simulated by the finite element method. The fluid flow that causes the fibers to deform is calculated by the lattice Boltzmann method. The method is extended from the two dimensional case to the three dimensional case. Results from simulation show the rigid fiber in simple shear flow produces a good agreement for orientation of a fiber relative to the theoretical study by Jeffery (1922). The flexible fiber exhibits an increase on the rotational period from the rigid fiber due to more deformation shape is revealed during rotation. The simulation technique demonstrates the ability to simulate fiber-fiber interactions to further study of relative viscosity of suspensions in shear flow. Simulation results show that fiber orientation and relative viscosity depend on the fiber characteristics (fiber aspect ratio, fiber flexibility, and volume fraction). The results are verified against known experimental measurements and theoretical results. The broad aim of this research is to better understand the behavior of fibers in fluid flow. It is hoped that future researchers may benefit from the new technique and algorithms developed here.

[Truncated abstract] The hydrodynamic forces on a marine pipeline and the local scour around it are the most serious and important issues in designing and maintaining pipelines. This thesis explores the vortex shedding phenomena for the flow over smooth surface and rough surface isolated cylinders. This thesis also explores the two-dimensional and three-dimensional scour process beneath offshore pipelines numerically. A series of numerical models are proposed in this dissertation for the prediction of flow characteristics and the time development of local scour around pipelines. All the models presented in this thesis are deliberately developed based on novel lattice Boltzmann method (LBM), because in recent years it has been considered as a serious alternative to standard computational fluid dynamics (CFD) as it is ideally suited to massively parallel computations. The lattice Boltzmann method is described in details to reveal how it recovers the Navier- Stokes equations. Various grid refinement schemes available in literature are discussed and a slightly modified new scheme is proposed to remove oscillatory solutions at high velocity change regime. The proposed scheme is then validated against bench mark tests for low Reynolds number flow. A turbulent model based on LBM is developed in order to predict the vortex shedding flow around an isolated square smooth surface cylinder. The various local and global flow parameters and structure of vortices are validated against experimental and numerical data available in literature. The model is then extended to investigate the vortex shedding flow over an isolated rough surface cylinder as it has an engineering significance in the design process of pipelines. The model is employed to investigate the influence of pipe roughness on various local and global parameters of flow. ... Significant part of this thesis is aimed at modelling flow and local scour around pipelines employing LBM and cellular automata (CA) methods. The erosion mechanism of the CA method available in literature for sand particles is improved by defining the threshold of sediment entrainment on bed in a similar manner to that employed in the traditional scour models. The predicted scour profiles for various incoming flow conditions are found to compare well with the experimental results reported in the literature. The existence of lee wake erosion due to continuous generation of vortex shedding in the lee of the pipelines is revealed. The time development of the maximum scour depth below the pipe is also found to be in good agreement with the experimental measurements reported in literature Finally, a three-dimensional flow and scour model is developed in order to explore the scour process beneath pipelines. It is revealed that the three-dimensionality effects are more pronounced near the span shoulder. On the other hand, there exists a two-dimensional scour regime in the vicinity of the middle section of the suspended pipe. It is found that the propagation speed of the scour hole in the sapnwise direction remains almost constant at all stages of scour process.