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A lattice Boltzmann equation model for thermal liquid film flowHantsch, Andreas 05 December 2013 (has links)
Liquid film flow is an important flow type in many applications of process engineering. For supporting experiments, theoretical and numerical investigations are required. The present state of the art is to model the liquid film flow with Navier--Stokes-based methods, whereas the lattice Boltzmann method is employed here. The final model has been developed within this treatise by means of a two-phase flow and a heat transfer model, and boundary and initial conditions. All these sub-models have been applied to simple test cases.
It could be found that the two-phase model is capable of solving flow phenomena with a large density ratio which has been shown impressively in conjunction with wall boundary conditions. The heat transfer model was tested against spectral method results with a transient non-uniform flow field. It was possible to find optimal parameters for computation. The final model has been applied to steady-state film flow, and showed very good agreement to OpenFOAM simulations. Tests with transient film flow demonstrated that the model is also able to predict these flow phenomena. / Flüssigkeitsfilmströmungen kommen in vielen verfahrenstechnischen Prozessen zum Einsatz. Zur Unterstützung von Experimenten sind theoretische und numerische Untersuchungen nötig. Stand der Technik ist es, Navier--Stokes-basierte Modelle zu verwenden, wohingegen hier die Lattice-Boltzmann-Methode verwendet wird. Das finale Modell wurde unter Verwendung eines Zweiphasen- und eines Wärmeübertragungsmodell entwickelt und geeignete Rand- und Anfangsbedingungen formuliert. Alle Untermodelle wurden anhand einfacher Testfälle überprüft.
Es konnte herausgefunden werden, dass das Zweiphasenmodell Strömungen großer Dichteunterschiede rechnen kann, was eindrucksvoll im Zusammenhang mit Wandrandbedingungen gezeigt wurde. Das Wärmeübertragungsmodell wurde gegen eine Spektrallösung anhand eines transienten und nichtuniformen Strömungsproblemes getestet. Stationäre Filmströmungen zeigten sehr gute Übereinstimmungen mit OpenFOAM-Lösungen und instationäre Berechungen bewiesen, dass das Model auch solche Strömungen abbilden kann.
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Liquid metal flows drive by gas bubbles in a static magnetic fieldZhang, Chaojie 02 February 2010 (has links) (PDF)
This thesis presents an experimental study which investigates the behaviour of gas bubbles rising in a liquid metal and the related bubble-driven flow under the influence of external DC magnetic fields. The experimental configuration considered here concerns a cylindrical container filled with the eutectic alloy GaInSn. Argon gas bubbles are injected through a single orifice located at the container bottom in the centre of the circular cross-section. A homogeneous magnetic field was generated by a Helmholtz configuration of a pair of water-cooled copper coils. The magnetic field has been imposed either in vertical direction parallel to the main bubble motion or in horizontal direction, respectively. A vertical magnetic field stabilizes and damps the liquid metal flow effectively. The temporal variations of the fluid velocity with time become smaller with increasing magnetic induction. The velocity magnitudes are decreased, and the velocity distributions along the magnetic field lines are smoothed. The flow field keeps the axisymmetric distribution. A horizontal magnetic field destabilizes and enhances the flow within a range of moderate Hartmann numbers (100 < Ha < 400). The flow becomes non-axisymmetric due to the non-isotropic influence of the magnetic field. In the meridional plane parallel to the field lines, the flow changes its direction from a downward to an upward motion. Enhanced downward flows were observed in the meridional plane perpendicular to the field lines. The liquid velocity in both planes shows strong, periodic oscillations. The fluid motion is dominated by large-scale structures elongated along the magnetic field lines over the entire chord lengths of the circular cross-section.
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Parallele Algorithmen für die numerische Simulation dreidimensionaler, disperser Mehrphasenströmungen und deren Anwendung in der Verfahrenstechnik / Parallel algorithms for the numerical simulation of 3-dimensional disperse multiphase flows and theire application in process technologyFrank, Thomas 30 August 2002 (has links)
Many fluid flow processes in nature and technology are characterized by the presence
and coexistence of two ore more phases. These two- or multiphase flows are furthermore
characterized by a greater complexity of possible flow phenomena and phase interactions
then in single phase flows and therefore the numerical simulation of these multiphase
flows is usually demanding a much higher numerical effort. The presented work
summarizes the research and development work of the author and his research group on
"Numerical Methods for Multiphase Flows" at the University of Technology, Chemnitz over the
last years. This work was focussed on the development and application of numerical
approaches for the prediction of disperse fluid-particle flows in the field of
fluid mechanics and process technology.
A main part of the work presented here is concerned with the modelling of different
physical phenomena in fluid-particle flows under the paradigm of the Lagrangian treatment
of the particle motion in the fluid. The Eulerian-Lagrangian approach has proved to be an
especially well suited numerical approach for the simulation of disperse multiphase flows.
On the other hand its application requires a large amount of (parallel) computational power
and other computational ressources. The models described in this work give a mathematical
description of the relevant forces and momentum acting on a single spherical particle in
the fluid flow field, the particle-wall interaction and the particle erosion to the wall.
Further models has been derived in order to take into account the influence of
particle-particle collisions on the particle motion as well as the interaction of the
fluid flow turbulence with the particle motion. For all these models the state-of-the-art
from literature is comprehensively discussed.
The main field of interest of the work presented here is in the area of development,
implementation, investigation and comparative evaluation of parallelization
methods for the Eulerian-Lagrangian approach for the simulation of disperse multiphase
flows. Most of the priorly existing work of other authors is based on shared-memory
approaches, quasi-serial or static domain decomposition approaches. These parallelization
methods are mostly limited in theire applicability and scalability to parallel computer
architectures with a limited degree of parallelism (a few number of very powerfull compute
nodes) and to more or less homogeneous multiphase flows with uniform particle concentration
distribution and minor complexity of phase interactions. This work now presents a novel
parallelization method developed by the author, realizing a dynamic load balancing
for the Lagrangian approach (DDD - Dynamic Domain Decomposition) and therefore leading
to a substantial decrease in total computation time necessary for multiphase flow
computations with the Eulerian-Lagrangian approach.
Finally, the developed and entirely parallelized Eulerian-Lagrangian approach MISTRAL/PartFlow-3D
offers the opportunity of efficient investigation of disperse multiphase flows with
higher concentrations of the disperse phase and the resulting strong phase interaction
phenomena (four-way coupling). / Viele der in Natur und Technik ablaufenden Strömungsvorgänge sind durch die
Koexistenz zweier oder mehrerer Phasen gekennzeichnet. Diese sogenannten Zwei- oder
Mehrphasensysteme zeichnen sich durch ein hohes Maß an Komplexität aus und
erfordern oft einen sehr hohen rechentechnischen Aufwand zu deren numerischer Simulation.
Die vorliegende Arbeit faßt langjährige Forschungs- und Entwicklungsarbeiten
des Autors und seiner Forschungsgruppe "Numerische Methoden für Mehrphasenströmungen"
an der TU Chemnitz zusammen, die sich mit der Entwicklung und Anwendung numerischer
Berechnungsverfahren für disperse Fluid-Partikel-Strömungen auf dem Gebiet
der Strömungs- und Verfahrenstechnik befassen.
Ein wesentlicher Teil der Arbeit befaßt sich mit der Modellierung unterschiedlicher
physikalischer Phänomene in Fluid-Partikel-Strömungen unter dem Paradigma der Lagrange'schen
Betrachtungsweise der Partikelbewegung. Das Euler-Lagrange-Verfahren hat sich als
besonders geeignetes Berechnungsverfahren für die numerische Simulation disperser
Mehrphasenströmungen erwiesen, stellt jedoch in seiner Anwendung auch höchste
Anforderungen an die Ressourcen der verwendeten (parallelen) Rechnerarchitekturen.
Die näher ausgeführten mathematisch-physikalischen Modelle liefern eine Beschreibung
der auf eine kugelförmige Einzelpartikel im Strömungsfeld wirkenden Kräfte
und Momente, der Partikel-Wand-Wechselwirkung und der Partikelerosion. Weitere Teilmodelle
dienen der Berücksichtigung von Partikel-Partikel-Stoßvorgängen und der
Wechselwirkung zwischen Fluidturbulenz und Partikelbewegung.
Der Schwerpunkt dieser Arbeit liegt im Weiteren in der Entwicklung, Untersuchung und vergleichenden
Bewertung von Parallelisierungsverfahren für das Euler-Lagrange-Verfahren zur Berechnung von
dispersen Mehrphasenströmungen. Zuvor von anderen Autoren entwickelte Parallelisierungsmethoden
für das Lagrange'sche Berechnungsverfahren basieren im Wesentlichen auf Shared-Memory-Ansätzen,
Quasi-Seriellen Verfahren oder statischer Gebietszerlegung (SDD) und sind somit in ihrer
Einsetzbarkeit und Skalierbarkeit auf Rechnerarchitekturen mit relativ geringer Parallelität
und auf weitgehend homogene Mehrphasenströmungen mit geringer Komplexität der Phasenwechselwirkungen
beschränkt. In dieser Arbeit wird eine vom Autor entwickelte, neuartige Parallelisierungsmethode
vorgestellt, die eine dynamische Lastverteilung für das Lagrange-Verfahren ermöglicht (DDD - Dynamic
Domain Decomposition) und mit deren Hilfe eine deutliche Reduzierung der Gesamtausführungszeiten
einer Mehrphasenströmungsberechnung mit dem Euler-Lagrange-Verfahren möglich ist.
Im Ergebnis steht mit dem vom Autor und seiner Forschungsgruppe entwickelten vollständig parallelisierten
Euler-Lagrange-Verfahren MISTRAL/PartFlow-3D ein numerisches Berechnungsverfahren zur Verfügung,
mit dem disperse Mehrphasenströmungen mit höheren Konzentrationen der dispersen Phase und
daraus resultierenden starken Phasenwechselwirkungen (Vier-Wege-Kopplung) effektiv untersucht
werden können.
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Coherent gas flow patterns in heterogeneous permeability fieldsSamani, Shirin 16 February 2012 (has links) (PDF)
Gas injection into saturated porous media has a high practical relevance. It is applied in
groundwater remediation (air sparging), in CO2 sequestration into saline aquifers, and
in enhanced oil recovery of petroleum reservoirs. This wide range of application
necessitates a comprehensive understanding of gas flow patterns that may develop
within the porous media and required modeling of multi-phase flow. There is an
ongoing controversy in literature, if continuum models are able to describe the complex
flow pattern observed in heterogeneous porous media, especially the channelized
stochastic flow pattern. Based on Selker’s stochastic hypothesis, a gas channel is
caused by a Brownian-motion process during gas injection. Therefore, the pore-scale
heterogeneity will determine the shape of the single stochastic gas channels. On the
other hand there are many studies on air sparging, which are based on continuum
modeling. Up to date it is not clear under which conditions a continuum model can
describe the essential features of the complex gas flow pattern. The aim of this study is
to investigate the gas flow pattern on bench-scale and field scale using the continuum
model TOUGH2. Based on a comprehensive data set of bench-scale experiments and
field-scale experiments, we conduct for the first time a systematic study and evaluate
the prediction ability of the continuum model.
A second focus of this study is the development of a “real world”-continuum model,
since on all scales – pore-scale, bench scale, field scale – heterogeneity is a key driver
for the stochastic gas flow pattern. Therefore, we use different geostatistical programs
to include stochastic conditioned and unconditioned parameter fields.
Our main conclusion from bench-scale experiments is that a continuum model, which is
calibrated by different independent measurements, has excellent prediction ability for
the average flow behavior (e.g. the gas volume-injection rate relation). Moreover, we
investigate the impact of both weak and strong heterogeneous parameter fields
(permeability and capillary pressure) on gas flow pattern. The results show that a
continuum model with weak stochastic heterogeneity cannot represent the essential
features of the experimental gas flow pattern (e.g., the single stochastic gas channels).
Contrary, applying a strong heterogeneity the continuum model can represent the
channelized flow. This observation supports Stauffer’s statement that a so-called subscale
continuum model with strong heterogeneity is able to describe the channelized
flow behavior. On the other hand, we compare the theoretical integral gas volumes with
our experiments and found that strong heterogeneity always yields too large gas
volumes.
At field-scale the 3D continuum model is used to design and optimize the direct gas
injection technology. The field-scale study is based on the working hypotheses that the
key parameters are the same as at bench-scale. Therefore, we assume that grain size and
injection rate will determine whether coherent channelized flow or incoherent bubbly
flow will develop at field-scale. The results of four different injection regimes were
compared with the data of the corresponding field experiments. The main conclusion is
that because of the buoyancy driven gas flow the vertical permeability has a crucial
impact. Hence, the vertical and horizontal permeability should be implemented
independently in numerical modeling by conditioned parameter fields.
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35 |
Coherent gas flow patterns in heterogeneous permeability fields: Coherent gas flow patterns in heterogeneous permeability fields: from bench-scale to field-scaleSamani, Shirin 02 August 2012 (has links)
Gas injection into saturated porous media has a high practical relevance. It is applied in
groundwater remediation (air sparging), in CO2 sequestration into saline aquifers, and
in enhanced oil recovery of petroleum reservoirs. This wide range of application
necessitates a comprehensive understanding of gas flow patterns that may develop
within the porous media and required modeling of multi-phase flow. There is an
ongoing controversy in literature, if continuum models are able to describe the complex
flow pattern observed in heterogeneous porous media, especially the channelized
stochastic flow pattern. Based on Selker’s stochastic hypothesis, a gas channel is
caused by a Brownian-motion process during gas injection. Therefore, the pore-scale
heterogeneity will determine the shape of the single stochastic gas channels. On the
other hand there are many studies on air sparging, which are based on continuum
modeling. Up to date it is not clear under which conditions a continuum model can
describe the essential features of the complex gas flow pattern. The aim of this study is
to investigate the gas flow pattern on bench-scale and field scale using the continuum
model TOUGH2. Based on a comprehensive data set of bench-scale experiments and
field-scale experiments, we conduct for the first time a systematic study and evaluate
the prediction ability of the continuum model.
A second focus of this study is the development of a “real world”-continuum model,
since on all scales – pore-scale, bench scale, field scale – heterogeneity is a key driver
for the stochastic gas flow pattern. Therefore, we use different geostatistical programs
to include stochastic conditioned and unconditioned parameter fields.
Our main conclusion from bench-scale experiments is that a continuum model, which is
calibrated by different independent measurements, has excellent prediction ability for
the average flow behavior (e.g. the gas volume-injection rate relation). Moreover, we
investigate the impact of both weak and strong heterogeneous parameter fields
(permeability and capillary pressure) on gas flow pattern. The results show that a
continuum model with weak stochastic heterogeneity cannot represent the essential
features of the experimental gas flow pattern (e.g., the single stochastic gas channels).
Contrary, applying a strong heterogeneity the continuum model can represent the
channelized flow. This observation supports Stauffer’s statement that a so-called subscale
continuum model with strong heterogeneity is able to describe the channelized
flow behavior. On the other hand, we compare the theoretical integral gas volumes with
our experiments and found that strong heterogeneity always yields too large gas
volumes.
At field-scale the 3D continuum model is used to design and optimize the direct gas
injection technology. The field-scale study is based on the working hypotheses that the
key parameters are the same as at bench-scale. Therefore, we assume that grain size and
injection rate will determine whether coherent channelized flow or incoherent bubbly
flow will develop at field-scale. The results of four different injection regimes were
compared with the data of the corresponding field experiments. The main conclusion is
that because of the buoyancy driven gas flow the vertical permeability has a crucial
impact. Hence, the vertical and horizontal permeability should be implemented
independently in numerical modeling by conditioned parameter fields.
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36 |
Liquid metal flows drive by gas bubbles in a static magnetic fieldZhang, Chaojie 18 January 2010 (has links)
This thesis presents an experimental study which investigates the behaviour of gas bubbles rising in a liquid metal and the related bubble-driven flow under the influence of external DC magnetic fields. The experimental configuration considered here concerns a cylindrical container filled with the eutectic alloy GaInSn. Argon gas bubbles are injected through a single orifice located at the container bottom in the centre of the circular cross-section. A homogeneous magnetic field was generated by a Helmholtz configuration of a pair of water-cooled copper coils. The magnetic field has been imposed either in vertical direction parallel to the main bubble motion or in horizontal direction, respectively. A vertical magnetic field stabilizes and damps the liquid metal flow effectively. The temporal variations of the fluid velocity with time become smaller with increasing magnetic induction. The velocity magnitudes are decreased, and the velocity distributions along the magnetic field lines are smoothed. The flow field keeps the axisymmetric distribution. A horizontal magnetic field destabilizes and enhances the flow within a range of moderate Hartmann numbers (100 < Ha < 400). The flow becomes non-axisymmetric due to the non-isotropic influence of the magnetic field. In the meridional plane parallel to the field lines, the flow changes its direction from a downward to an upward motion. Enhanced downward flows were observed in the meridional plane perpendicular to the field lines. The liquid velocity in both planes shows strong, periodic oscillations. The fluid motion is dominated by large-scale structures elongated along the magnetic field lines over the entire chord lengths of the circular cross-section.
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37 |
Numerical modeling of compositional two-phase reactive transport in porous media with phase change phenomena including an application in nuclear waste disposalHuang, Yonghui 03 December 2018 (has links)
Non-isothermal compositional two-phase flow is considered to be one of the fundamental physical processes in the field of water resources research. The strong non-linearity and discontinuity emerging from phase transition phenomena pose a serious challenge for numerical modeling. Recently, Lauser et al.[1] has proposed a numerical scheme, namely the Nonlinear Complementary Problem (NCP), to handle this strong non-linearity. In this work, the NCP is implemented at both local and global levels of a Finite element algorithm.
In the former case, the NCP is integrated into the local thermodynamic equilibrium calculation. While in the latter one, it is formulated as one of the governing equations. The two different formulations have been investigated through several well established benchmarks and analyzed for their efficiency and robustness. In the second part of the thesis, the presented numerical formulations are applied for application and process studies in the context of nuclear waste disposal in Switzerland. Application studies comprehend the coupling between multiphase transport model and complex bio-geo-chemical process to investigate the degradation of concrete material due to two major reactions: carbonation and Aggregate Silica Reaction(ASR). The chemical processes are simplified into a lookup table and cast into the transport model via source and sink term. The efficiency and robustness of the look-up table are further compared with a fully reactive transport model.
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Parallele Algorithmen für die numerische Simulation dreidimensionaler, disperser Mehrphasenströmungen und deren Anwendung in der VerfahrenstechnikFrank, Thomas 21 June 2002 (has links)
Many fluid flow processes in nature and technology are characterized by the presence
and coexistence of two ore more phases. These two- or multiphase flows are furthermore
characterized by a greater complexity of possible flow phenomena and phase interactions
then in single phase flows and therefore the numerical simulation of these multiphase
flows is usually demanding a much higher numerical effort. The presented work
summarizes the research and development work of the author and his research group on
"Numerical Methods for Multiphase Flows" at the University of Technology, Chemnitz over the
last years. This work was focussed on the development and application of numerical
approaches for the prediction of disperse fluid-particle flows in the field of
fluid mechanics and process technology.
A main part of the work presented here is concerned with the modelling of different
physical phenomena in fluid-particle flows under the paradigm of the Lagrangian treatment
of the particle motion in the fluid. The Eulerian-Lagrangian approach has proved to be an
especially well suited numerical approach for the simulation of disperse multiphase flows.
On the other hand its application requires a large amount of (parallel) computational power
and other computational ressources. The models described in this work give a mathematical
description of the relevant forces and momentum acting on a single spherical particle in
the fluid flow field, the particle-wall interaction and the particle erosion to the wall.
Further models has been derived in order to take into account the influence of
particle-particle collisions on the particle motion as well as the interaction of the
fluid flow turbulence with the particle motion. For all these models the state-of-the-art
from literature is comprehensively discussed.
The main field of interest of the work presented here is in the area of development,
implementation, investigation and comparative evaluation of parallelization
methods for the Eulerian-Lagrangian approach for the simulation of disperse multiphase
flows. Most of the priorly existing work of other authors is based on shared-memory
approaches, quasi-serial or static domain decomposition approaches. These parallelization
methods are mostly limited in theire applicability and scalability to parallel computer
architectures with a limited degree of parallelism (a few number of very powerfull compute
nodes) and to more or less homogeneous multiphase flows with uniform particle concentration
distribution and minor complexity of phase interactions. This work now presents a novel
parallelization method developed by the author, realizing a dynamic load balancing
for the Lagrangian approach (DDD - Dynamic Domain Decomposition) and therefore leading
to a substantial decrease in total computation time necessary for multiphase flow
computations with the Eulerian-Lagrangian approach.
Finally, the developed and entirely parallelized Eulerian-Lagrangian approach MISTRAL/PartFlow-3D
offers the opportunity of efficient investigation of disperse multiphase flows with
higher concentrations of the disperse phase and the resulting strong phase interaction
phenomena (four-way coupling). / Viele der in Natur und Technik ablaufenden Strömungsvorgänge sind durch die
Koexistenz zweier oder mehrerer Phasen gekennzeichnet. Diese sogenannten Zwei- oder
Mehrphasensysteme zeichnen sich durch ein hohes Maß an Komplexität aus und
erfordern oft einen sehr hohen rechentechnischen Aufwand zu deren numerischer Simulation.
Die vorliegende Arbeit faßt langjährige Forschungs- und Entwicklungsarbeiten
des Autors und seiner Forschungsgruppe "Numerische Methoden für Mehrphasenströmungen"
an der TU Chemnitz zusammen, die sich mit der Entwicklung und Anwendung numerischer
Berechnungsverfahren für disperse Fluid-Partikel-Strömungen auf dem Gebiet
der Strömungs- und Verfahrenstechnik befassen.
Ein wesentlicher Teil der Arbeit befaßt sich mit der Modellierung unterschiedlicher
physikalischer Phänomene in Fluid-Partikel-Strömungen unter dem Paradigma der Lagrange'schen
Betrachtungsweise der Partikelbewegung. Das Euler-Lagrange-Verfahren hat sich als
besonders geeignetes Berechnungsverfahren für die numerische Simulation disperser
Mehrphasenströmungen erwiesen, stellt jedoch in seiner Anwendung auch höchste
Anforderungen an die Ressourcen der verwendeten (parallelen) Rechnerarchitekturen.
Die näher ausgeführten mathematisch-physikalischen Modelle liefern eine Beschreibung
der auf eine kugelförmige Einzelpartikel im Strömungsfeld wirkenden Kräfte
und Momente, der Partikel-Wand-Wechselwirkung und der Partikelerosion. Weitere Teilmodelle
dienen der Berücksichtigung von Partikel-Partikel-Stoßvorgängen und der
Wechselwirkung zwischen Fluidturbulenz und Partikelbewegung.
Der Schwerpunkt dieser Arbeit liegt im Weiteren in der Entwicklung, Untersuchung und vergleichenden
Bewertung von Parallelisierungsverfahren für das Euler-Lagrange-Verfahren zur Berechnung von
dispersen Mehrphasenströmungen. Zuvor von anderen Autoren entwickelte Parallelisierungsmethoden
für das Lagrange'sche Berechnungsverfahren basieren im Wesentlichen auf Shared-Memory-Ansätzen,
Quasi-Seriellen Verfahren oder statischer Gebietszerlegung (SDD) und sind somit in ihrer
Einsetzbarkeit und Skalierbarkeit auf Rechnerarchitekturen mit relativ geringer Parallelität
und auf weitgehend homogene Mehrphasenströmungen mit geringer Komplexität der Phasenwechselwirkungen
beschränkt. In dieser Arbeit wird eine vom Autor entwickelte, neuartige Parallelisierungsmethode
vorgestellt, die eine dynamische Lastverteilung für das Lagrange-Verfahren ermöglicht (DDD - Dynamic
Domain Decomposition) und mit deren Hilfe eine deutliche Reduzierung der Gesamtausführungszeiten
einer Mehrphasenströmungsberechnung mit dem Euler-Lagrange-Verfahren möglich ist.
Im Ergebnis steht mit dem vom Autor und seiner Forschungsgruppe entwickelten vollständig parallelisierten
Euler-Lagrange-Verfahren MISTRAL/PartFlow-3D ein numerisches Berechnungsverfahren zur Verfügung,
mit dem disperse Mehrphasenströmungen mit höheren Konzentrationen der dispersen Phase und
daraus resultierenden starken Phasenwechselwirkungen (Vier-Wege-Kopplung) effektiv untersucht
werden können.
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