Дисертації: "Computational Fluids Mechanic"

1

Andrade, Luiz Fernando de Souza. "Animação de jatos oscilantes em fluidos viscosos usando SPH em GPU." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-08082014-113954/.

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Nos últimos anos, o estudo de métodos de animação de escoamento de fluidos tem sido uma área de intensa pesquisa em Computação Gráfica. O principal objetivo desse projeto é desenvolver novas técnicas em GPGPU baseadas na arquitetura CUDA para simular o escoamento de fluidos não-newtonianos, tais como fluidos viscoplásticos e viscoelásticos. Ao invés dos tradicionais métodos com malha diferenças finitas e elementos finitos, essas técnicas são baseadas em uma discretização lagrangeana das equações de governo desses fluidos através do método sem malha conhecido como SPH (Smoothed Particle Hydrodynamics)
I n recent years, the study of methods of animating fluid flow has been an area of intense research in Computer Graphics. The main objective of this project is to develop new techniques based on the CUDA GPGPU architecture to simulate the flow of non-Newtonian fluids, such as viscoelastic and viscoplastic fluids. Instead of traditional methods with mesh - finite differences and finite elements, these techniques are based on a Lagrangian discretization of the governing equations of these fluids through the mesh free method known as SPH (Smoothed Particle Hydrodynamics)

2

Latour, Gillien. "Modélisation et simulation 3D des écoulements et transports au sein d'un bassin versant." Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP009.

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L'équilibre entre les besoins anthropiques en eau et la disponibilité des ressources hydrologiques souterraines est menacé par la présence de polluants dans les sols et les sous-sols. Afin d'étudier les risques de contamination des nappes phréatiques par des polluants issus d'activités nucléaires, le CEA (Commissariat à l'Énergie Atomique et aux énergies alternatives) utilise des modèles hydrogéologiques pour simuler des scénarios potentiels. Dans une volonté d'amélioration de la précision de ces simulations, la présente thèse propose des modèles tridimensionnels d'écoulement des eaux souterraines et du transport de polluants à l'échelle du bassin versant. Ces modèles permettent d'intégrer de nombreux mécanismes physiques négligés dans les modèles mono et bidimensionnels. Toutefois, la mise en œuvre des modèles 3D nécessite des paramètres adaptés ainsi que d'importantes ressources numériques. Dans un premier temps, nous avons mis en place une méthode de calibration des modèles d'écoulement 1D+2D et 3D, décomposée en une étape de calibration de la perméabilité par la méthode des points-pilotes, suivie par une étape de calibration des paramètres du modèle de capillarité par la méthode de Nelder-Mead. Cette méthode a permis l'obtention de paramètres dédiés aux modèles 3D, et les résultats ont été sujet à une publication. Sous l'hypothèse d'une perméabilité verticalement homogène, les calibrations des champs de perméabilité des modèles 1D+2D et 3D ont produits des résultats similaires et une interpolation du modèle 1D+2D vers le modèle 3D est alors pertinente. À l'inverse, les calibrations des paramètres du modèle de capillarité produisent des ensembles très différents. Des méthodes de calibration propres aux modèles 3D s'avèrent nécessaires. La comparaison des ressources numériques nécessaires à la calibration des modèles 1D+2D et 3D a mis en valeurs les importants coûts numériques nécessaires à l'exploitation des modèles 3D de l'écoulement.Pour limiter ces coûts, nous avons mis en œuvre deux méthodes numériques d'amélioration de l'efficacité sur les modèles 3D utilisés. La première méthode est le raffinement adaptatif du maillage (AMR). Cette méthode consiste à raffiner localement le maillage dans les zones d'intérêt au fur et à mesure de la simulation. En appliquant cette méthode sur les équations du transport en présence d'un écoulement stationnaire, nous avons retrouvé les résultats d'une simulation raffinée, tant sur des cas théoriques que sur un cas réaliste complexe. Nous avons également amorcé l'intégration des méthodes de raffinement adaptatif du maillage dans les solveurs de l'écoulement, mais une mise en œuvre complète et pleinement fonctionnelle nécessite encore des efforts. La seconde méthode numérique utilisée pour augmenter l'efficacité des simulations 3D est la méthode du double maillage. Appliquée aux phénomènes de transport en présence d’écoulement transitoires, cette méthode différencient les discrétisations spatiales des équations du transport et de l'écoulement, ce qui permet de raffiner uniquement un des deux maillages. Nous montrons alors que le raffinement du maillage dédié au transport est plus important que le raffinement maillage dédié à l'écoulement pour une localisation précise du panache de polluant et de ses concentrations. En associant cette méthode au raffinement adaptatif du maillage dédié au transport sur une colonne 1D et dans un domaine réaliste 3D, nous sommes parvenus à réduire d'un facteur 100 les temps de calculs sur des maillages raffinés deux fois en dégradant de façon négligeable la précision des résultats
The balance between human water needs and the availability of groundwater resources is threatened by the presence of pollutants in sub-surfaces. To study the risks of groundwater contamination from pollutants originating from nuclear activities, the CEA (French Alternative Energies and Atomic Energy Commission) uses hydro-geological models to simulate potential scenarios. In an effort to enhance the precision of these simulations, this thesis proposes three-dimensional models of groundwater flow and pollutant transport at the watershed scale. These models allow the incorporation of numerous physical mechanisms neglected in mono- and bi-dimensional models. However, the implementation of 3D models requires tailored parameters and significant computational resources.Initially, we established a calibration method for 1D+2D and 3D flow models, divided into a permeability calibration step using the pilot points method, followed by a capillarity model parameter calibration step using the Nelder-Mead method. This method yielded a correct parameter set for 3D models, and the results were subject to publication. Assuming vertically homogeneous permeability, calibrations of permeability fields for 1D+2D and 3D models produced similar results, making interpolation from the 1D+2D model to the 3D model possible. In contrast, calibrations of capillarity model parameters produced very different sets. Specific calibration methods for 3D models are therefore necessary. A comparison of the computational resources required for calibrating 1D+2D and 3D models highlighted the significant numerical costs associated with the operation of 3D flow models.To mitigate these costs, we implemented two numerical methods to enhance the efficiency of the employed 3D models. The first method is an adaptive mesh refinement (AMR), involving local mesh refinement in areas of interest during the simulation. By applying this method to transport equations in the presence of steady flow, we achieved results similar to those of a refined simulation, both for theoretical cases and a complex realistic scenario. We also initiated the integration of adaptive mesh refinement methods into flow solvers, but complete and fully functional implementation still requires further efforts.The second numerical method used to increase the efficiency of 3D simulations is the double-mesh method. Applied to transport in the presence of transient flow, this method distinguishes spatial discretizations of transport and flow equations, allowing for the refinement of only one of the two meshes. We demonstrate that refinement of the transport-dedicated mesh is more critical than refinement of the flow-dedicated mesh for precise localization of the pollutant plume and its concentrations. By combining this method with adaptive mesh refinement dedicated to transport in a 1D column and in a realistic 3D domain, we succeeded in reducing computation times by a factor of 100 on twice-refined meshes, with negligible degradation in result accuracy

3

Farhat, Hikmat. "Studies in computational methods for statistical mechanics of fluids." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0026/NQ50157.pdf.

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4

Hughes, Michael. "Computational magnetohydrodynamics." Thesis, University of Greenwich, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284683.

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5

Betancourt, Arturo. "Computational study of the heat transfer and fluid structure of a shell and tube heat exchanger." Thesis, Florida Atlantic University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10172609.

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A common technique to improve the performance of shell and tube heat exchangers (STHE) is by redirecting the flow in the shell side with a series of baffles. A key aspect in this technique is to understand the interaction of the fluid dynamics and heat transfer. Computational fluid dynamics simulations and experiments were performed to analysis the 3-dimensional flow and heat transfer on the shell side of an STHE with and without baffles. Although, it was found that there was a small difference in the average exit temperature between the two cases, the heat transfer coefficient was locally enhanced in the baffled case due to flow structures. The flow in the unbaffled case was highly streamed, while for the baffled case the flow was a highly complex flow with vortex structures formed by the tip of the baffles, the tubes, and the interaction of flow with the shell wall.

6

Peshkin, David Annesley. "Computational fluid dymanics using transputer systems." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335585.

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7

Marshall, G. S. "Muiticomponent fluid flow computation." Thesis, Teesside University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384659.

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8

Hunsaker, Doug F. "Evaluation of an Incompressible Energy-Vorticity Turbulence Model for Fully Rough Pipe Flow." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/1068.

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Traditional methods of closing the Boussinesq-based Reynolds-averaged Navier-Stokes equations are considered, and suggestions for improving two-equation turbulence models are made. The traditional smooth-wall boundary conditions are shown to be incorrect, and the correct boundary conditions are provided along with sample solutions to traditional models. The correct boundary condition at a smooth wall for dissipation-based turbulence models is that which forces both the turbulent kinetic energy and its first derivative to zero. Foundations for an energy-vorticity model suggested by Phillips are presented along with the near-smooth-wall behavior of the model. These results show that at a perfectly smooth wall, the turbulent kinetic energy may approach the wall at a higher order than is generally accepted. The foundations of this model are used in the development of a k-λ model for fully rough pipe flow. Closure coefficients for the model are developed through gradient-based optimization techniques. Results of the model are compared to results from the Wilcox 1998 and 2006 k-ω models as well as four eddy-viscosity models. The results show that the Phillips k-λ model is much more accurate than other models for predicting the relationship between Reynolds number and friction factor for fully rough pipe flow. However, the velocity profiles resulting from the model deviate noticeably from the law of the wall.

9

Alarcón, Oseguera Francisco. "Computational study of the emergent behavior of micro-swimmer suspensions." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/394065.

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It is known that active particles induce emerging patterns as a result of their dynamic interactions, giving rise to amazing collective motions, such as swarming or clustering. Here we present a systematic numerical study of self-propelling particles; our main goal is to characterize the collective behavior of suspensions of active particles as a result of the competition among their propulsion activity and the intensity of an attractive pair potential. Active particles are modeled using the squirmer model. Due to its hydrodynamic nature, we are able to classify the squirmer swimmer activity in terms of the stress it generates (referred to as pullers or pushers). We show that these active stresses play a central role in the emergence of collective motion. We have found that hydrodynamics drive the coherent swimming between swimmers while the swimmer direct interactions, modeled by a Lennard-Jones potential, contributes to the swimmers' cohesion. This competition gives rise to two different regimes where giant density fluctuations (GDF) emerge. These two regimes are differentiated by the suspension alignment; one regime has GDF in aligned suspensions whereas the other regime has GDF of suspensions with an isotropic orientated state. All the simulated squirmer suspensions shown in this study were characterized by a thorough analysis of global properties of the squirmer suspensions as well as a complementary cluster analysis. Active matter refers generically to systems composed of self-driven units, active particles, each capable of converting stored or ambient free energy into systematic movement. Examples of active systems are found at all length scales and could be classified in living and nonliving systems such as microorganisms, tissues and organisms, animal groups, self- propelled colloids and artificial nanoswimmers. Specifically, at the micro and nano scale we find an enormous range of interesting systems both biological and artificial; e.g. spermatozoa that fuse with the ovum during fertilization, the bacteria that inhabit our guts, the protozoa in our ponds, the algae in the ocean; these are but a few examples of a wide biological spectrum. In the artificial world we have self- healing colloidal crystals and membranes as well as self- assembled microswimmers and robots. Experiments in this field are now developing at a very rapid pace and new theoretical ideas are needed to bring unity to the field and identify "universal" behavior in these internally driven systems. One important feature of active matter is that their elements can develop emergent, coordinated behavior; collective motion constitutes one of the most common and spectacular example. Collective motion is ubiquitous and at every scale, from herds of large mammals to amoeba and bacteria colonies, down to the cooperative behavior of molecular motors in the cell. The behavior of large fish schools and the dance of starling flocks at dusk are among the most spectacular examples. From a physical perspective collective motion emerges from a spontaneous symmetry breaking that allows for long-range orientational orden The different mechanisms responsible for such symmetry breaking are still not completely understood. We have performed a systematic numerical study of interactive micro-swimmer suspensions building on the squirmer model, introduced by Lighthill. Since the squirmer identifies systematically the hydrodynamic origin of self-propulsion and stress generation it provides a natural scheme to scrutinize the impact that the different features associated to self-propulsion in a liquid medium have in the collective dynamics of squirmer suspensions. In this abstract we describe the simulation scheme and how squirmers are modeled, then some of the main results are discussed and finally we conclude emphasizing the main implications of the results obtained.
Los sistemas activos se definen como materiales fuera del equilibrio termodinámico compuestos por muchas unidades interactuantes que individualmente consumen energía y colectivamente generan movimiento o estreses mecánicos. Ejemplos se pueden encontrar en un enorme rango de escalas de longitud, desde el mundo biológico hasta artificial, incluyendo organismos unicelulares, tejidos y organismos pluricelulares, grupos de animales, coloides auto-propulsados y nano-nadadores artificiales. Actualmente se están desarrollando experimentos en este campo a un ritmo muy veloz, en consecuencia son necesarias nuevas ideas teóricas para traer unidad al campo de estudio e identificar comportamientos “universales” en estos sistemas propulsados internamente. El objetivo de esta tesis es el estudiar mediante simulaciones numéricas, el comportamiento colectivo de un modelo de micro-nadadores. En particular, el modelo de squirmers, donde el movimiento del fluido es axi-simétrico. Existen estructuras coherentes que emergen de estos sistemas así que, el entender si las estructuras coherentes son generadas por la firma hidrodinámica intrínseca de los squirmers individuales o por un efecto de tamaño finito se vuelve algo de primordial importancia. Nosotros también estudiamos la influencia que tiene la geometría en la aparición de estructuras coherentes, la interacción directa entre las partículas, la concentración, etc.

10

Dhruv, Akash. "A Multiphase Solver for High-Fidelity Phase-Change Simulations over Complex Geometries." Thesis, The George Washington University, 2021. http://pqdtopen.proquest.com/#viewpdf?dispub=28256871.

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Complex interactions between solid, liquid and gas occur in many practical engineering applications, and are often difficult to quantify experimentally. A few examples include boiling over solid heaters, solidification melt-dynamics in metal casting, and convective cooling of electronic components. With the availability of scalable computational tools, high-fidelity simulations can provide new insight into these phenomena and answer open questions. In the present work, a multiphase solver is presented which can simulate problems involving phase transition over complex geometries. The dynamics of liquid-gas interface are modeled using a level-set technique, which utilizes Ghost Fluid Method (GFM) to account for sharp jump in pressure, velocity, and temperature across the multiphase boundary. The fluid-solid interactions are modeled using an Immersed Boundary Method (IBM) which uses a Moving Least Squared (MLS) reconstruction to calculate fluid-flow around the solid, along with an additional GFM forcing to model its effect on pressure, temperature and Conjugate Heat Transfer (CHT). The resulting three dimensional solver is fully explicit in time and uses a fractional step method for Navier-Stokes, energy, and mass transfer equations. Validation and verification cases are presented to demonstrate the accuracy of the solver in comparison to experimental and analytical problems, and results of high fidelity pool boiling simulations in varying gravity environments are discussed in detail.

11

Emmanuelli, Gustavo. "An Assessment of State Equations of Air for Modeling a Blast Load Simulator." Thesis, Mississippi State University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10979719.

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When an explosive detonates above ground, air is principally the only material involved in the transmission of shock waves that can result in damage. Hydrodynamic codes that simulate these explosions use equations of state (EOSs) for modeling the behavior of air at these high-pressure, high-velocity conditions. An investigation is made into the effect that the EOS selection for air has on the calculated overpressure-time waveforms of a blast event. Specifically, the ideal gas, Doan-Nickel, and SESAME EOSs in the SHAMRC code were used to reproduce experiments conducted at the Blast Load Simulator (BLS), a large-scale shock tube operated by the U.S. Army Engineer Research and Development Center, that consisted of subjecting an instrumented rigid box at three angles of orientation inside the BLS to a blast environment. Numerical comparisons were made against experimentally-derived confidence intervals using peak values and several error metrics, and an attempt was made to rank the EOS based on performance. Issues were noted with the duration of decay from maximum pressure to negative phase that resulted in a general underprediction of the integrated impulse regardless of EOS, while the largest errors were noted for gages on faces at 45 to 90 degrees from the initial flow direction. Although no significant differences were noticed in the pressure histories from different EOSs, the ideal gas consistently ranked last in terms of the error metrics considered and simultaneously required the least computing resources. Similarly, the Doan-Nickel EOS slightly performed better than SESAME while requiring additional wallclock time. The study showed that the Doan-Nickel and SESAME EOSs can produce blast signatures with less errors and more matches in peak pressure and impulse than the ideal gas EOS at the expense of more computational requirements.

12

Ichinose, Matthew Hiroki. "Fluid Agitation Studies for Drug Product Containers using Computational Fluid Dynamics." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1980.

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At Amgen, the Automated Vision Inspection (AVI) systems capture the movement of unwanted particles in Amgen's drug product containers. For quality inspection, the AVI system must detect these undesired particles using a high speed spin-stop agitation process. To better understand the fluid movements to swirl the particles away from the walls, Computational Fluid Dynamics (CFD) is used to analyze the nature of the two phase flow of air and a liquid solution. Several 2-D and 3-D models were developed using Fluent to create simulations of Amgen's drug product containers for a 1 mL syringe, 2.25 mL syringe, and a 5 mL cartridge. Fluid motion and potential bubble formations were studied within the liquid/gas domain inside the container by varying parameters such as viscosity, angular velocity, and surface tension. Experiments were conducted using Amgen's own equipment to capture the images of the spin-stop process and validate the models created in Fluent. Observations were made to see the effects of bubble formation or splashing during spin-down to rest. The numerical and experimental results showed favorable comparison when measuring the meniscus height or the surface profile between the air and liquid. Also, at high angular velocity and dynamic viscosity, the container experiences instabilities and bubble formations. These studies indicate that CFD can be used as an useful and important tool to study fluid movement during agitation and observe any undesirable results for quality inspection.

13

Shelley, Jonathan Knighton. "Incorporating Computational Fluid Dynamics Into The Preliminary Design Cycle." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd979.pdf.

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14

Siwale, Namwawa Alice. "Modeling of flow in impeller stirred tanks using computational fluids dynamics." Master's thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/6761.

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Includes bibliographical references (leaves 63-68).
The efficiency of mixing processes in impeller agitated tanks depends highly on the hydrodynamics. Computational fluids dynamics (CFD) provides a method of predicting the complex flow structures in stirred tanks. As with any approximate numerical method, CFD methods are subject to errors due to assumptions in the underlying mathematical models, as well as errors due to the numerical solution procedures. The aim of this thesis was to present a CFD method that accurately models the hydrodynamic properties of the 110w in stirred tanks. The general purpose CFD software Fluent 6. 1 was used to develop the model of a laboratory scale stirred tank. Numerical experiments were conducted to investigate the effects of the computational grid density, discretization schemes, turbulence models and impeller modelling method on the accuracy of the simulated flow. The results were validated with Laser Doppler Velocimetry data from the literature. It was found that the density of the numerical grid had more influence on the predicted turbulent quantities than on the mean velocity components. For the mean velocity components, reasonable agreement with the experimental data was observed even on relatively coarse grids. The choice of discretization scheme was found to have significant effect on the predicted turbulent kinetic energy and Power numbers. Very good agreement with experimental data was achieved for both these flow variables when higher order discretization schemes were used on fine grids. This is an important finding as it suggests that the generally reported underestimation of turbulence in literature is caused by numerical errors in the CFD simulation as opposed to inadequacies in the turbulence models as suggested by most researchers. Steady-state and time-dependent impeller models were compared and found to have little effect on the mean velocity and turbulent kinetic energy. However impeller Power numbers calculated from the time-dependent simulations were found to be in better agreement with the experimental values. A comparison was also made between the standard k-s and RNG models. It was found that the standard k-s turbulence model gave better predictions of the flow than the RNG- k-s turbulence model.

15

Aharon, Ofer S. M. Massachusetts Institute of Technology. "Stress distributions around hydrofoils using computational fluid dynamics." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46382.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaf 108).
This research describes the reciprocal influence between two foils, vertically and horizontally oriented, on each other for different gaps between them. Those cases are the focus part of a bigger process of lowering significantly the drag of a ship when hydrofoils are attached to its hull. The research results are based on CFD analyses using the ADINA software. In order to verify the CFD process, a comparison was made between analytical, experimental and ADINA?s results for a single foil. The chosen foil was the famous Clark-Y foil; however a correction to its geometry was made using the Unigraphics software. Using the corrected geometry with an analytical solution well detailed and explained, the results of the CFD model were compared to experimental and analytical solutions. The matching of the results and the obtained accuracy are very high and satisfactory. In addition, the research contains an examination of the results when one of the boundary conditions is changed. Surprisingly, it was discovered that the FREE slip condition along the foil is much closer to reality than the NO slip condition. Another examination was stretching horizontally the foil and checking the pressure distribution behavior. Those results met exactly the expectations. As for the main core of this research, both the bi-plane case and the stagger case were found to be less effective than using a single foil. The conclusion of those investigations is that using those cases a few decades ago was for a structural reason rather than stability or speed. Since this research is very wide but also deep in its knowledge, references and academic work, many future research works may be based on it or go on from its detailed stages.
by Ofer Aharon.
S.M.

16

Abdulrazaq, Muhammed. "Extensional Instability in Complex Fluids: A Computational Study." Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-290228.

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In this study, instability and failure in complex fluids (Elastoviscoplastic fluids) is explored using the classic Considère (F˙ < 0) and stress curvature (σ¨ < 0) criteria. Employing the Saramito model, numerical simulation of the extensional protocol on non-Newtonian fluids is carried out. Validation is firstly performed (with a purely viscoelastic model) and in general found to be in agreement with previous works. Parameter variation of the Bingham number (Bi), capillary number (Ca) and extension rate (ε˙) is then undertaken. It is found out that for Oldroyd-B based fluids, the stress curvature condition almost always occurs from inception of the flow for all cases. Additionally, increasing surface tension has a stabilizing effect on the extending fluid when it is below a critical value, above which it aids breakup. Increasing the yield stress, though, delays the onset of instability, but reduces the final length of the extending filament. At mild to high extension rates, the Considère criterion and the extension at the maximum stress are suit-able indicators of the final extension at strain-to-break(εST B). Furthermore, the rate of the of necking instability till final breakup varies with the εST B at moderate to high ε˙.
I denna studie undersöks instabilitet och misslyckande i komplexa vätskor (Elastoviskoplas-tiska vätskor) med den klassiska Considère (F˙ < 0) och stresskurvatur (σ¨ < 0) kriterier. Genom att använda Saramito-modellen utförs numerisk simulering av det utökade protokol-let på icke-newtonska vätskor. Valideringen utförs först (med en rent viskoelastisk modell) och i allmänhet visar sig överensstämma med tidigare verk.Parametervariation av Bingham-numret (Bi), kapillärnummer (Ca) och förlängningshastighet (ε˙) genomförs sedan. Det har visat sig att för Oldroyd-B-baserade vätskor, uppträder stresskrökningstillståndet nästan alltid från början av flödet i alla fall. Dessutom har ökande ytspänningen stabiliserande effekt på den utsträckande vätskan när den är under ett kritiskt värde, över vilket den underlättar uppbrytning. En ökning av sträckgränsen fördröjer dock instabiliteten men minskar den slutliga längden på det utsträckta filamentet. Vid milda till höga utvidgningshastigheter är Considère-kriteriet och förlängningen vid maximal spänning lämpliga indikatorer för den slutliga förlängningen vid spänning till brott (εST B). Vidare varierar frekvensen av instabilitet i halsen till slutlig upplösning med εST B vid måttlig till hög ε˙.

17

Mallone, Kevin Charles. "A more robust wall model for use with the two-equation turbulence model." Thesis, University of Hertfordshire, 1995. http://hdl.handle.net/2299/14149.

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The applicability of computational fluid dynamics (CFD) modelling schemes to turbulent wall-bounded flows is a matter of concern. In the near-wall region of bounded flows, the standard high Reynolds number k-e model is not valid and requires the use of empirical wall models to mimic the behaviour of this region. A theoretical study of the physics of prevalent wall modelling techniques showed that the velocity distribution took no account of the pressure gradient. To determine the effect of this shortcoming, a typical transient three-dimensional flow was analysed using current CFD methods and the results compared with experimental flow measurements. Consideration of these results showed that the 'traditional' wall model was unable to replicate observed flow features in the near-wall region: further analysis of the computational results confirmed that these poor flow predictions arose from the inability of the model to consider local pressure gradient effects. Consequently, a strong case was made for a more robust wall model for use in conjunction with the standard high Reynolds number k-e model. A number of boundary layer analyses were reviewed and Coles' law of the wake (1956) presented as a viable candidate for the development of a new wall modelling scheme. In theory, Coles' law (1956) provides a description of bounded flows under arbitrary pressure gradients up to the point of near-separation and may be extended to the study of reversed flows. A generic algorithm for Coles' law was prepared and used to study the fundamental test cases of U-bend and backward facing step flows. In a comparison between documented experimentation, 'conventional' CFD modelling and Coles' law models of these flows, the Coles' law model was shown to provide a viable alternative to 'traditional' schemes. Consequently, the Coles' law model of the near-wall region, being valid for pressure-driven flows, offers an extension to the range of flows for which the standard high Reynolds number k-e model may be used.

18

Aggarwal, Nishith. "Computational viscoelastic drop dynamics and rheology." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 122 p, 2008. http://proquest.umi.com/pqdweb?did=1456285651&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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19

Rhodes, Norman. "The modelling of ventilation-related flows using computational fluid dynamics." Thesis, London South Bank University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386261.

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20

Al-Rashed, Mohsen Hassan Jaber. "A study of reactive precipitation processes using computational fluid dynamics." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286284.

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21

Boromand, Arman. "Computational Studies on Multi-phasic Multi-componentComplex Fluids." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480500319335545.

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22

Fu, Song. "Computational modelling of turbulent swirling flows with second-moment closures." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267917.

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This work focuses on the simulation of turbulent swirling flows within the framework of second-moment closure. The main objectives are to assess the performance of currently available turbulence models in predicting such flows, and to develop new closure models which would further enhance current predictive ability, and hence, to provide a reliable turbulence model for engineering applications that would help the design process and reduce the development costs of industrial combustion systems. Attention is confined to isothermal flows, and predictions have been carried out for three major swirling cases: a weakly and a strongly swirling free jet and a confined strongly swirling flow in which an annular swirling stream is discharged together with a non-swirling central jet into a suddenly enlarging circular chamber. In the last case, mass transfer has also been examined by predicting the behaviour of an inert scalar tracer with which the central jet has been laced. The existing turbulence models examined are the standard versions of the k — e Boussinesq-viscosity model, the algebraic stress closure and the differential stress closure (BVM, ASM and DSM, respectively), as well as modified ASM and DSM variants. One outcome of this study is that neither the standard versions of the BVM, ASM and DSM nor their previously modified forms examined here predict adequately swirling-flow behaviour. An important conclusion emerging from preliminary efforts has been that the algebraic approximation of stress transport in terms of the transport of turbulence energy—which is a widely used practice—is fundamentally flawed in the presence of swirl. Specifically, the method returns a physically unrealistic behaviour of the normal stresses. It is this conclusion which eventually led to the ASM methodology being discarded and to the exclusive use of the differential methodology. Within the framework of differential closures, two new pressure-strain models have been proposed, namely the Isotropization of Production and Convection Model (IPCM) and the Cubic Quasi-Isotropic Model (CQIM). The former emerged as an extension of the standard DSM approach with the inclusion of the convection tensor into the turbulence isotropization mechanism, whereas the latter follows from a more rational and fundamental approach in which non-linear anisotropy effects have been incorporated, with the resulting model made to satisfy the limit of two-dimensional turbulence. Comparisons between predicted solutions and measurements for swirling flow show that the IPCM produces a marked improvement over all the other models considered, while it does not significantly alter the behaviour of the standard stress closure in non-swirling conditions. Only very limited improvement is achieved by the CQIM, however, despite its success in predicting nearly homogeneous shear flows. The merits and weaknesses of all the models examined are discussed in detail, and the IPCM is recommended as the best approach for predictions of swirling flows. Within the study of the confined case, considerations were extended to the modelling of scalar transport by a second-moment flux closure, and comparisons are made between eddy-diffusivity and flux-closure calculations and experimental data. Computational results show that the distribution of the scalar field is primarily governed by aero-dynamic features. There are indications, however, that the flux model is superior to the eddy-diffusivity model.

23

Duffy, Graham James. "A computational study of particulate deposition from turbulent gas flows." Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334338.

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24

Morrison, D. J. "Experimental and computational modelling of the flows in service reservoirs." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323928.

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25

TIAN, BINYU. "COMPUTATIONAL AEROELASTIC ANALYSIS OF AIRCRAFT WINGS INCLUDING GEOMETRY NONLINEARITY." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1070398084.

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26

Simpson, Benjamin Alec Field. "A computational study of gas leak jets relevant to offshore structures." Thesis, University of Hertfordshire, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268043.

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In the present research three dimensional, incompressible turbulent jet flows from sharp edged rectangular orifices were numerically simulated. Preliminary studies employing the standard k-E turbulence model stressed the sensitivity of the flow to the specification of turbulence quantities at the inlet. The definition of correct turbulence quantities at the inflow of large eddy simulations was also shown to be crucial for realistic simulations. Consequently, a novel computationally inexpensive boundary condition, that provided turbulence data with known energy, was developed and programmed into a commercial finite element code. The large eddy simulations provided instantaneous data that demonstrated the emergence of complex flow patterns within a short axial distance. The upstream geometry from the jet exit was not included in the present simulations. Therefore, the swirling motion and vortical structures observed could not be related to the different rates of contraction upstream of the discharge plane. In addition, saddle-backed profiles were observed in the long axis of the jet stream. The saddlebacked profiles were formed by a combination of the secondary motions and curvature of the streamlines due to the entrained fluid entering normally to the main jet stream. Turbulence quantities were quantified from the large eddy simulations and showed similar trends to the verifying experimental data. The round jet assumption used in the past to study gas leakage from pipework was found to be invalid in the near field. The simulations clearly illustrate differences between the flow field, the turbulence field, and the coherent structures of a rectangular jet and a round jet. Regions of high and low mixing between the escaping flammable gas and the surrounding air were identified in the large eddy simulations. Furthermore, the coherent structures in the shear layers that resulted in a flapping motion in the lateral direction of the jet, were recognised as important entrainment mechanisms. Numerical techniques have been developed that can be used to investigate gas leakage in detail. The time dependent numerical data provides valuable insight into the mixing mechanisms of the local gas/air mixture thus aiding the safer design of offshore structures.

27

Rashid, Tariq Mahmood. "Computational modelling of dynamic wind effects relevant to compliant offshore structures." Thesis, University of Hertfordshire, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332219.

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28

Stipcich, Goran. "High-order methods for computational fluid dynamics." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7764.

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2010/2011
In the past two decades, the growing interest in the study of fluid flows involving discontinuities, such as shocks or high gradients, where a quadratic-convergent method may not provide a satisfactory solution, gave a notable impulse to the employment of high-order techniques. The present dissertation comprises the analysis and numerical testing of two high-order methods. The first one, belonging to the discontinuous finite-element class, is the discontinuous control-volume/finite-element method (DCVFEM) for the advection/ diffusion equation. The second method refers to the high-order finite-difference class, and is the mixed weighted non-oscillatory scheme (MWCS) for the solution of the compressible Euler equations. The methods are described from a formal point of view, a Fourier analysis is used to assess the dispersion and dissipation errors, and numerical simulations are conducted to confirm the theoretical results.
XXIV Ciclo
1980

29

Aichouni, Mohamed. "Development and decay of turbulent pipe flows : an experimental and computational study." Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305082.

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30

Unwin, Anna Theresa. "Variational characterizations of steady two-dimensional vortex motions." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291456.

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31

Glover, Ian Christopher. "Some convergence enhancing schemes for systems of conservation laws." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335828.

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32

Deligiannis, Christos. "Two-dimensional vortex methods : analysis, development and applications." Thesis, University of Brighton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273864.

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33

Mason, Darren M. "The nonlinear evolution of the elliptical instability : an example of inertial wave breakdown." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299329.

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34

Crossley, Peter Simon. "On spectral methods for shock wave calculations." Thesis, Manchester Metropolitan University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361577.

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35

Dawes, A. S. "Natural co-ordinates and high speed flows : a numerical method for reactive gases." Thesis, Cranfield University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333184.

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36

Barber, Robert William. "Numerical modelling of jet-forced circulation in reservoirs using boundary-fitted coordinate systems." Thesis, University of Salford, 1990. http://usir.salford.ac.uk/26561/.

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Throughout the past decade, interest has grown in the use of boundary-fitted coordinate systems in many areas of computational fluid dynamics. The boundary-fitted technique provides an exact method of implementing finite-difference numerical schemes in curved flow geometries and offers an alternative solution procedure to the finite-element method. The unavoidable large bandwidth of the global stiffness matrix, employed in finite-element algorithms, means that they are computationally less efficient than corresponding finite-difference schemes. As a consequence, the boundary-fitted method offers a more efficient process for solving partial differential flow equations in awkwardly shaped regions. This thesis describes a versatile finite-difference numerical scheme for the solution of the shallow water equations on arbitrary boundary-fitted non-orthogonal curvilinear grids. The model is capable of simulating flows in irregular geometries typically encountered in river basin management. Validation tests have been conducted against the severe condition of jet-forced flow in a circular reservoir with vertical side walls, where initial reflections of free surface waves pose major problems in achieving a stable solution. Furthermore, the validation exercises have been designed to test the computer model for artificial diffusion which may be a consequence of the numerical scheme adopted to stabilise the shallow water equations. The thesis also describes two subsidiary numerical studies of jet-forced recirculating flow in circular cylinders. The first of these implements a Biot-Savart discrete vortex method for simulating the vorticity in the shear layers of the inflow jet, whereas the second employs a stream function/vorticity-transport finite-difference procedure for solving the two-dimensional Navier-Stokes equations on a distorted orthogonal polar mesh. Although the predictions from the stream function/vorticity-transport model are confined to low Reynolds number flows, they provide a valuable set of benchmark velocity fields which are used to confirm the validity of the boundary-fitted shallow water equation solver.

37

Popat, Nilesh R. "Steep capillary waves on gravity waves." Thesis, University of Bristol, 1989. http://hdl.handle.net/1983/78695ee9-b923-4374-b70c-6589b4215241.

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The frequent presence of ripples on the free surface of water. on both thin film flows and ponds or lakes motivates this theoretical investigation into the propagation of ripples on gravity waves. These ripples are treated as "slowly-varying" waves in a reference frame where the gravity wave flow is steady. The methods used are those of the averaged Lagrangian (Whitham 1965,1967,1974) and the averaged equations of motion (Phillips 1966) which are shown to be equivalent. The capillary wave modulation is taken to be steady in the reference frame which brings the gravity wave, or gravity driven flow, to rest. Firstly the motion over ponds or lakes is considered. Linear capillary-gravity waves are examined in order to set the scene. Crapper's (1957) exact finite-amplitude waves are examined next to show the actual behaviour of the flow field. The underlying gravity driven flow is that of pure gravity waves over an' "infinite" depth liquid. These gravity waves are modelled with "numerically exact" solutions for periodic plane-waves. The initial studies are inviscid and show that steep gravity waves either "absorb" or "sweep-up" a range of capillary waves or, alternatively, cause them to break in the vicinity of gravity wave crests. Improvements on the theory are made by including viscous dissipation of wave energy. This leads to a number of solutions approaching "stopping velocities" or the "stopped waves solution". In addition to these effects "higher-order dispersion" is introduced for weakly nonlinear waves near linear caustics. This clarifies aspects of the dissipation results and shows that wave reflection sometimes occurs. Secondly, waves on thin film flows are considered. Linear capillary-gravity waves are again examined in order to set the scene. Kinnersley's (1957) exact finite-amplitude waves are examined next to show the actual behaviour of the flow field. The underlying gravity driven flow is given by shallow water gravity waves. No modelling of these is necessary simply because they are included within Whitham's or Phillips' equations ab initio. This study is inviscid and shows the unexpected presence of critical velocities at which pairs of solution branches originate. iii

38

Nagai, Toshiki. "Space-time Extended Finite Element Method with Applications to Fluid-structure Interaction Problems." Thesis, University of Colorado at Boulder, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10844711.

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This thesis presents a space-time extended finite element method (space-time XFEM) based on the Heaviside enrichment for transient problems with moving interfaces, and its applications to the fluid-structure interaction (FSI) analysis. The Heaviside-enriched XFEM is a promising method to discretize partial differential equations with discontinuities in space. However, significant approximation errors are introduced by time stepping schemes when the interface geometry changes in time. The proposed space-time XFEM applies the finite element discretization and the Heaviside enrichment in both space and time with elements forming a space-time slab. A simple space-time scheme is introduced to integrate the weak form of the governing equations. This scheme considers spatial intersection configuration at multiple temporal integration points. Standard spatial integration techniques can be applied for each spatial configuration. Nitsche's method and the face-oriented ghost-penalty method are extended to the proposed space-time XFEM formulation. The stability, accuracy and flexibility of the space-time XFEM for various interface conditions including moving interfaces are demonstrated with structural and fluid problems. Moreover, the space-time XFEM enables analyzing complex FSI problems using moving interfaces, such as FSI with contact. Two FSI methods using moving interfaces (full-Eulerian FSI and Lagrangian-immersed FSI) are studied. The Lagrangian-immersed FSI method is a mixed formulation of Lagrangian and Eulerian descriptions. As solid and fluid meshes are independently defined, the FSI is computed between non-matching interfaces based on Nitsche's method and projection techniques adopted from computational contact mechanics. The stabilized Lagrange multiplier method is used for contact. Numerical examples of FSI and FSI-contact problems provide insight into the characteristics of the combination of the space-time XFEM and the Lagrangian-immersed FSI method. The proposed combination is a promising method which has the versatility for various multi-physics simulations and the applicability such as optimization.

39

Iverson, Jared M. "Computational fluid dynamics validation of buoyant turbulent flow heat transfer." Thesis, Utah State University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1550153.

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Computational fluid dynamics (CFD) is commonly implemented in industry to perform fluid-flow and heat-transfer analysis and design. Turbulence model studies in literature show that fluid flows influenced by buoyancy still pose a significant challenge to modeling. The Experimental Fluid Dynamics Laboratory at Utah State University constructed a rotatable buoyancy wind tunnel to perform particle image velocimetry experiments for the validation of CFD turbulence models pertaining to buoyant heat-transfer flows. This study validated RANS turbulence models implemented within the general purpose CFD software STAR-CCM+, including the k – ε models: realizable two-layer, standard two-layer, standard low-Re, v² – f, the k- ω models from Wilcox and Menter, and the Reynolds stress transport and Spalart - Allmaras models. The turbulence models were validated against experimental heat flux and velocity data in mixed and forced convection flows at mixed convection ratios in the range of 0.1 ≤ Gr/Re² ≤ 0.8. The k- εε standard low-Re turbulence model was found most capable overall of predicting the fluid velocity and heat flux of the mixed convection flows, while mixed results were obtained for forced convection.

40

Janosky, Kyle. "Computational Fluid Dynamics Modeling and Lab Testing of Hydraulic Spool Valves." Cleveland State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=csu1600280326762048.

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41

陳彤{272b21} and Tong Chen. "Numerical computations on free-surface flow." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31238245.

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42

Chen, Tong. "Numerical computations on free-surface flow /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21020292.

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43

Lindstens, Robin. "Computational fluid dynamics calculations of a spillway’s energy dissipation." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-417950.

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To make sure that a dam is safe it is important to have good knowledge about the energy dissipation in the spillway. Physical hydraulic model tests are reliable when investigating how the water flow behaves on its way through the spillway. The problem with physical model testing is that it is both expensive and time consuming, therefore computational fluid dynamics, CFD, is a more feasible option. This projects focuses on a spillway located in Sweden that Vattenfall R&D built a physical model of to simulate the water discharge and evaluate the energy dissipation in order to rebuild the actual spillway. The main purpose of this project is to evaluate if the physical hydraulic test results can be reproduced by using CFD, and obtain detailed results about the flow that could not be obtained by physical testing. There are several steps that need to be completed to create a CFD-model. The first step is to create a geometry, then the geometry needs to be meshed. After the meshing the boundary conditions need to be set and the different models, multiphase model and the viscous model, need to be defined. Next step is to set the operating conditions and decide which solution method that will be used. Then the simulation can be run and the results can get extracted. In this project two CFD simulations were performed. The first simulation was to be compared with the physical hydraulic model test results and the second CFD simulation was of the rebuilt spillway. The results proved that the physical model test results could be recreated by using CFD. It also gave a better understanding of how the energy dissipation was in the spillway and indicates that the reconstruction of the actual spillway was successful since the new spillway both had a higher water discharge capacity and better energy dissipation.

44

Deng, Xiaolong. "APPLICATIONS OF COMPUTATIONAL FLUID DYNAMICS TO PLANETARY ATMOSPHERES." UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/711.

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Computational Fluid Dynamics (CFD) has been applied to many areas. As one of the most important fluids, the atmosphere is closely related to people’s life. Studying the atmospheres on other planets can help people understand the Earth’s atmosphere and the climate and weather phenomena in it. Because of the complexity of a planetary atmosphere and the limitation of observations, applying CFD to the study of planetary atmospheres is becoming more and more popular. This kind of CFD simulations will also help people design the mission to the extra planets. In this dissertation, through CFD simulations, we studied the three important phenomena in a planetary atmosphere: vortices, zonal winds and clouds. The CFD model Explicit Planetary Isentropic Coordinate (EPIC) Global Circulation Model (GCM) was applied in these simulations. Dynamic simulations of the Great Dark Spots (GDS) on Neptune and the Uranian Dark Spot (UDS) were performed. In this work, constructed zonal wind profiles and vertical pressure-temperature profile were constructed based on the observational data. Then, we imported a two-flux radiation model with two-band absorption coefficients into EPIC to study the seasonal changes on Uranus. Finally, a methane cloud model was imported to study the cloud formation around a great vortex and its effects on the vortex. In the process of the dynamic simulations of Neptune’s atmosphere and its vortices in it, the parameters about the background and the vortex itself were investigated to try to fit the observational results. We found that a small gradient of background absolute vorticity near a GDS is needed to sustain a great vortex in the atmosphere. The drift rate and oscillations of a GDS are closely related to the zonal wind profile and the vortex characteristics. The dynamic simulations of the UDS suggested why it is hard to observe a great vortex on Uranus and indicated that a region of near constant absolute vorticity appearing at ∼28◦N in the zonal wind profile is possibly recommended to the sustainability of the UDS.With the two-flux radiation model, we simulated the seasonal change of the zonal wind profile on Uranus. The observational temperature distribution and global convection were also achieved. With the methane cloud model, we simulated the poleward cloud above great vortices on both Neptune and Uranus. The results suggested that the cloud model can help the GDS on Neptune to keep its shape and moderate its oscillations. Similarly, it can also help the UDS to keep its form.

45

Chhunchha, Aakash C. "Aerodynamic Heating Analysis of Re-entry Space Capsule Using Computational Fluid Dynamics." Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10752510.

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The present study deals with solving two-dimensional Reynolds Averaged Navier-Stokes equations for the Fire II re-entry capsule using Computational Fluid Dynamics (CFD). The primary goal is to model the aero thermodynamic flow characteristics around the capsule and estimate the surface heat flux distribution. Mach number value of 15.16 is chosen as a free stream condition corresponding to an altitude of 50 km. Taking advantage of the symmetry, only a quarter portion of the geometry is considered to generate the volume mesh for the simulation. The numerical models and convergence techniques that are implemented by the CFD solver are thoroughly described.

Special attention has been paid to validate the code. The value of shock stand-off distance obtained by means of benchmark empirical formulation is compared to the CFD analysis. An additional comparison between the simulated results and the approximated engineering correlations of convective stagnation point heat fluxes is made to ensure the validity of the obtained results. Overall, a satisfactory agreement is observed between the estimated values by engineering correlations and those predicted by the numerical solver.

46

Del, Toro Adam. "Computational Fluid Dynamics Analysis of Butterfly Valve Performance Factors." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1456.

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Butterfly valves are commonly used in industrial applications to control the internal flow of both compressible and incompressible fluids. A butterfly valve typically consists of a metal disc formed around a central shaft, which acts as its axis of rotation. As the valve's opening angle is increased from 0 degrees (fully closed) to 90 degrees (fully open), fluid is able to more readily flow past the valve. Characterizing a valve's performance factors, such as pressure drop, hydrodynamic torque, flow coefficient, loss coefficient, and torque coefficient, is necessary for fluid system designers to account for system requirements to properly operate the valve and prevent permanent damage from occurring. This comparison study of a 48-inch butterfly valve's experimental performance factors using Computational Fluid Dynamics (CFD) in an incompressible fluid at Reynolds numbers ranging approximately between 105 to 106 found that for mid-open positions (30-60 degrees), CFD was able to appropriately predict common performance factors for butterfly valves. For lower valve angle cases (10-20 degrees), CFD simulations failed to predict those same values, while higher valve angles (70-90 degrees) gave mixed results. (152 pages)

47

Zoueshtiagh, Farzam. "Experimental and computational study of spiral patterns in granular media underneath a rotating fluid." Thesis, University of Warwick, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247353.

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48

Burström, Per. "Computational Fluid Dynamics of Processes in Iron Ore Grate-Kiln Plants." Doctoral thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17118.

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Computational Fluid Dynamics (CFD) approaches have been developed to studypollution reduction in the manufacturing phase and heat transfer in the packed beds of iron ore pellets. CFD is a versatile tool that can be applied to study numerous problems in fluid mechanics. In the present thesis it is used, verified and validated to reveal the fluid mechanics of a couple of processes taking place during the drying and sintering of iron ore pellets. This is interesting in itself and can facilitate the optimization of the production as to product quality of the pellets, reduced energy consumption and reduction of emissions such as NOx and CO2. The practical aim with the pollution reduction research project is to numerically study the use of Selective Non-Catalytic Reduction (SNCR) technologies in gratekiln pelletizing plants for NOx reduction which had, to the best knowledge of the author, never been used in this context before despite that it is commonly used in cement and waste incineration plants. The investigation is done in several stages: 1)Reveal if it is possible to use the technique with the two most commonly reagents, ammonia and urea. 2) Derive a chemistry model for cyanuric acid (CA) so that this reagent also can be scrutinized. 3) Compare the reagents urea and CA in the gratekiln pelletizing process.A CFD model was developed and numerical simulations were carried out solving the flow field. A model for spray injection into the grate was then included in the model enabling a study of the overall mixing between the injected reagent droplets and the NOx polluted air. The results show that the SNCR technique with urea and CA may reduce the amount of NOx in the grate-kiln process under certain conditions while ammonia fails under the conditions investigated. The work also lays grounds for continued development of the proposed chemistry model by the adding of reactions to the RAPRENOx-process for CA as reagent, facilitating an extension to ammonia and urea as reagents.The grate-kiln plant consists of a grate, a rotating kiln and an annular cooler. The pellets are loaded onto the grate to shape a bed with a mean height of about 0.2 m. The pellets in LKABs processes consist mainly of magnetite and different additives chosen to fit the demand from the customer. Throughout the grate a temperature gradient is formed in the bed. This gradient should be as even as possible throughout the grate to ensure an even quality of the pellets. Method to study this numerically is the second main task in this thesis. The aim is to find out how temperature distributions in the bed can be modeled and adjusted. Of special interest is how the incoming process gas, leakage, and the detailed composition of the pellet bed influence the heat transfer through the bed. To achieve the goals and create a trustful model for the heat transfer through the packed bed the model must be build up in steps. Heat transfer to a bed of iron ore pellets is therefore examined numerically on several scales and with three methods: a one-dimensional continuous model, a discrete three-dimensional model and traditional computational fluid dynamics.In a first study the convective heat transport in a relatively thin porous layer ofmonosized particles is set-up and computed with the one-dimensional continuous model and the discrete three-dimensional model. The size of the particles is only one order of magnitude smaller than the thickness of the layer. For the three-dimensional model the methodology applied is Voronoi discretization with minimization of dissipation rate of energy. The discrete model captures local effects, including low heat transfer in sections with low speed of the penetrating fluid and large velocity and temperature variations in a cross section of the bed. The discrete and continuousmodel compares well for low velocities for the studied uniform boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The influence is larger from an increase in pellet diameter to bed height ratio than from increased velocity. In a second study the discrete model is compared to simulations performed with CFD. If local values are of importance the discrete model should always be used but if mean predictions are sufficient the CFD model isan attractive alternative that is easy to couple to the physics up- and downstream the packed bed. The good agreement between the discrete and continuous model furthermore indicates that the discrete model may be used also for non-Stokian flow in the transitional region between laminar and turbulent flow, as turbulent effects show little influence of the overall heat transfer rates in the continuous model.
Godkänd; 2015; 20150407 (burper); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Per E.C. Burström Ämne: Strömningslära/Fluid Mechanics Avhandling: Computational Fluid Dynamics of Processes in Iron Ore Grate-Kiln Plants Opponent: Professor Xue-Song Bai, Avd för strömningsteknik, Institutionen för energivetenskaper, Lunds tekniska högskola, Lund Ordförande: Professor Staffan Lundström, Avd för strömningslära och experimentell mekanik, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Torsdag 4 juni kl 13.00 Plats: E231, Luleå tekniska universitet

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Salim, Salim Mohamed. "Computational study of wind flow and pollutant dispersion near tree canopies." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12077/.

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Air quality in urban and industrial complexes is of great importance owing to the many implications on human and environmental health. Air pollution in built-up areas is typically associated with traffic exhaust emissions. High pedestrian level concentrations are the result of a non trivial combination of pollutant sources, climate and city morphological configurations. The increase of urbanisation puts a strain on city resources, resulting in increased use of transport and a denser and more compact urban fabric. The consequence of such a change in city morphology exacerbates current human air pollution exposure. There have been several Computational Fluid Dynamics (CFD) studies on air pollution problems in urban areas, which have largely centred on employing the conventional Reynolds-Averaged Navier-Stokes (RANS) approach, and in all of these investigations, the RANS models have been reported to numerically overpredict pollutant concentration levels when compared to wind tunnel (WT) measurements. In addition, the majority of previous investigations have failed to account for the aerodynamic effects of trees, which can occupy a significant portion of typical urban street canyons. The presence of trees aggravates the pollutant concentration at pedestrian level by altering the air circulation and ventilation. Trees act as obstacles to the airflow, reducing wind velocity within street canyons and restricting air exchange with the above-roof flow. As a result fewer pollutants are dispersed out of the canyon. To address shortcomings of previous numerical investigations, the work undertaken in this project has two main objectives. The study first aims to implement Large Eddy Simulation (LES) to improve the flow and concentration predictions, and second to demonstrate the aerodynamic impacts of trees. A wall y+ approach is used to determine the computational grid configuration and corresponding RANS turbulence model. The approach is evaluated in the present numerical study and is found to be exceptionally useful in resolving flow structures near shear zones, particularly in tree-lined canyons. This allows for the appropriate mesh resolution to be selected, when taking into account a compromise between prediction accuracy and computational cost. In part one of the project, the prediction accuracy of the pollutant dispersion within tree-free urban street canyons of width to height ratios W/H = 1 and W/H=2, are examined using two steady-state RANS turbulence closure models - the standard k-ε and Reynolds Stress Model (RSM) and LES coupled with the advection-diffusion method for species transport. The numerical results, which include the statistical properties of pollutant dispersion, e.g. the mean concentration distributions, the time-evolution and three-dimensional spreads of the pollutant, are then compared to WT measurements available from the online database (CODASC, 2008) www.codasc.de. The accuracy and computational cost of both numerical approaches are compared. The time-evolution of the pollutant concentration (for LES only) and the mean values are presented. It is observed that amongst the two RANS models, RSM performs better than standard k-ε except at the centreline of the canyon walls. However, LES, although more computationally expensive, does better than RANS. A supplementary investigation is performed to illustrate that unsteady RANS (URANS) is not a suitable replacement for LES when wishing to resolve the internally induced fluctuations of flow and concentration fields. URANS fails to capture the transient mixing process. Part two of the research extends the study from the tree-free street canyons by investigating the aerodynamic influence of tree plantings. Configurations of W/H=1 with single row of trees and W/H=2 with two rows of trees are simulated. In both cases, two tree crown porosities are studied, one for a loosely (Pvol = 97.5%) and another for a densely (Pvol = 96%) packed tree crown, corresponding to pressure loss coefficients λ = 80 m-1 and λ = 200 m-1, respectively. Results of the tree-lined cases are then compared to the tree-free street canyons from the previous investigation. It is observed that the presence of trees reduces the in-canyon circulation and air exchange, thus increasing the overall concentration levels. Similar to the tree-free cases, LES performs better than RANS. In addition, it is shown that a wider street W/H = 2 with two rows of trees promotes better air ventilation and circulation with lower pollutant accumulation at pedestrian level, as opposed to a narrow street W/H = 1 with one row of trees. This is also true for tree-free cases.

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Bezzo, Fabrizio. "Design of a general architecture for the integration of process engineering simulation and computational fluid dynamics." Thesis, Imperial College London, 2001. http://hdl.handle.net/10044/1/7142.

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