Segui questo link per vedere altri tipi di pubblicazioni sul tema: Stratified flow.
Tesi sul tema "Stratified flow"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Stratified flow".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Kurban, Adib Paulo Abdalla. "Stratified liquid-liquid flow". Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7553.
Testo completo
2
Bourban, Sebastien E. "Stratified shallow flow modelling". Thesis, Open University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664520.
Testo completoAbstract (sommario):
Environmental hydraulics covers a very wide range of applications including free surface flows in rivers. estuaries and lakes. To find engineering solutions to environmental hydraulics problems. 3D numerical modelling is nowadays widely used. However. the computation of sharp spatial gradients (such as found in stratified estuaries and lakes. around plumes near outfalls along rivers and coasts or in exchange areas of high shear). and the modelling of these processes along steep bathymetric slopes (such as found at the edge of dredged channels or of the continental shelf) remains a challenge. In addition. crude assumptions (such as the hydrostatic assumption) are often made to the primary differential equations in order to simplify the problem and enable long term prediction of environmental hydraulic changes. In this thesis. a robust adaptive mesh displacement (AMD) method is implemented and validated against the lock exchange case in particular. The AMD method aims at vertically focusing nodes within each water column to capture sharp gradients. while reducing the number of nodes or requiring prior knowledge of the flow structure. Second. a direct computation of dynamic pressure is introduced based on the equation of vertical momentum and validated against the analytical potential flow theory solution of a source-sink pair. Dynamic pressure is necessary to model destratification recirculation devices. or flow over dredge channel. or solitary waves. for instance. This direct computation method makes the hydrostatic assumption redundant. Third. a new advection scheme is implemented. whose main advantage is simplicity averaging over Riemann problems without solving them. while excessive numerical viscosity is compensated for by using high-resolution MUSCL type reconstruction. Recommendations are made in this thesis to extend the advection scheme developed herein for tracer advection to the non-linear shallow water equations. to the diffusion terms and to turbulence closure laws within the same finite element framework.
3
Rea, Suzanne. "Stratified flow at T-junctions". Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287195.
Testo completo
4
Ng, Tzuu Shing. "Interfacial structure of stratified pipe flow". Thesis, Imperial College London, 2002. http://hdl.handle.net/10044/1/11274.
Testo completo
5
Shaha, Jonathan. "Phase interactions in transient stratified flow". Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/8653.
Testo completo
6
Iial-Awad, Ahmad Salmeh. "Stratified flow in the built environment". Thesis, University of Hertfordshire, 2006. http://hdl.handle.net/2299/14350.
Testo completoAbstract (sommario):
Stratified flow in an environmental chamber has been investigated. The chamber of dimensions (7.5m long, 5.6m wide and 3.0m) at the University of Hertfordshire has been used. Sets of experiments investigating the effect of the major flow parameters such as airflow rate, jet momentum, flow conditions and height of the air supply device have been conducted. Results have been obtained to evaluate the flow characteristics and thermal stratification mechanism. The study has demonstrated the validity of using smoke visualization to evaluate the stratified flow characteristics such as interface level height, stratified layer thickness, and degree of stratification. The effects of both hot and cold airflow rates in the ranges of (0.0 to 8.0 m3 /min) were investigated. The flow characteristics vary depending on the flow parameters and the experimental conditions. The effect of supply terminal and extract terminal at various airflow rates on the flow characteristics is experimentally investigated. It has been found that relative influence of inertia and buoyancy forces resolves the stratified flow characteristics. The stratification interface level height and the ventilation flow rates are two main factors in the design of natural ventilation system. The results can be used to obtain a good estimation of the effectiveness of a ventilation system at design stage. Experimental work was carried out using ceiling jet to supply hot and cold air to a confined space, to investigate the effect of jet momentum in breaking and mixing the stratified layer. The flow of high momentum was supplied downward from the ceiling. The magnitude of momentum needed depends on the degree of stratification, stratified layer interface level height and the stratification conditions. It can be seen that the jet momentum has significant influence on the mixing of the stratified flow characteristics. The results indicated that once the momentum was initiated a mixed flow grew in the occupied zone above the floor. The height of this zone depends on the stratified flow characteristics, and the temperature and momentum of the ceiling jet. Another area of experimentation was the inversion of input airflow supplies. In this case, the flow of high buoyancy was supplied upward, whilst the flow of high momentum was supplied downward from the ceiling. The stratified layer lost its stability and broke down due to the drag and tearing of cold air penetrated downward from higher levels. The compound effect of these two conditions will circulate the air in the whole space and disturb the stability of the stratified layer to reach fully mixed flow A comprehensive definition of the degree of stratification was formulated. Analytical solutions were developed for the stratified layer thickness and location as a function of temperature gradient and airflow ratios. These expressions were calibrated using the experimental results. The critical momentum needed to breakdown the stratified layer also evaluated. Comparisons with previous studies where also carried out. It was found that the stratified layer interface level height is dependent on the ratio of airflow rate and geometrical effects. If mixed flow is desired then the cold inflow aperture should be located higher than the hot inflow aperture, whiles the interface level height is not located at the exhaust aperture height. The critical vertical momentum necessary in order to break down a stratified layer has been found to depend on the stratified layer interface level height. A semi-empirical formula based on the present experimental results has been developed to predict the critical vertical momentum for given stratified conditions. Based on the present experimental results, the effect of momentum is greater than the effect of buoyancy and the time needed to break down the stratified layer is considerable less than the time it takes to stratify. Experimental data also demonstrate a ventilation method for increasing the occupied zone height without breaking down the stratified layer.
7
Feng, Yanhua. "Stably stratified shear flow over complex terrain". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264359.
Testo completo
8
Omar, Hanan. "Intrusion flow into a density stratified resevoir". Thesis, Omar, Hanan (2016) Intrusion flow into a density stratified resevoir. PhD thesis, Murdoch University, 2016. https://researchrepository.murdoch.edu.au/id/eprint/30247/.
Testo completoAbstract (sommario):
Steady two-dimensional flows from an angled structure into a lake or a reservoir where the interface between the intrusion and the ambient fluid separates from a solid wall is considered. The fluid is assumed to be of finite depth and the incoming channel makes an angle _ with the horizontal axis. The problem is formulated using conformal mapping and integral equation techniques and the resulting problem is solved using a surface angle approach. The shape of the interface is computed for a range of entry angle and flow rate. Exact solutions are presented at a high flow rate and compared with the solutions to nonlinear problem. Solutions with waves are shown to exist on the interface at small flow rate and these are computed at very small entry angles using a physical plane method. The case in which the lake or the reservoir is stratified in density is also considered and separation height is determined for different values of the stratification. In all cases, the parameter space in which steady solutions exist is studied and limiting solutions are obtained. The results have implications for the design of efficient inflow structures for reservoirs and for water quality management.
9
Siqueira, Renato do Nascimento. "Transport and mixing processes in stratified flow". Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/34335.
Testo completoAbstract (sommario):
The processes of transport and mixing in stratified open channel flows are investigated in this thesis. Detailed measurements of velocity and salinity were conducted, through the use of Laser-Induced Fluorescence (LIP) technique together with Laser Doppler anemometry, so that the effects of secondary current and stratification on the flow behaviour could be analysed. Two configurations were investigated: a rectangular open channel, and a compound open channel. For each configuration, four different stratification levels were analysed. The main flow characteristics, such as corner flow and velocity dip in a rectangular channel, and the twin vortices formed in compound channels, were found to be affected by stratification. In order to understand the mechanisms involved in secondary flow generation, the vorticity balance was carried out. Through the vorticity balance, the contribution of each term in the longitudinal vorticity equation could be evaluated. The mechanisms involved in the turbulence generation were also verified through the turbulent kinetic energy (TKE) budget. One of the contributions of this work refers to the understanding of the effects of stratification on turbulence and secondary flow generation. The exchange coefficients of momentum and solute were also investigated. These coefficients were found to depend not only on stratification level but also on other flow parameters, like for instance the aspect ratio. A new formulation is proposed for narrow channels, but more research is necessary in order to evaluate the effect of other parameters on the exchange coefficients.
10
Chilakamarri, Kiran Babu. "Rotating and stratified fluids /". The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612163036.
Testo completo
11
Sit, Ming-fai. "Computation of stratified flow past three dimensional surface mounted obstacles /". [Hong Kong] : University of Hong Kong, 1988. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12431060.
Testo completo
12
Gargallo, Gallego Mireia. "Countercurrent flow limitations in horizontal stratified flows of air and water". Karlsruhe : FZKA, 2004. http://bibliothek.fzk.de/zb/berichte/FZKA7018.pdf.
Testo completo
13
Skopovi, Ivan 1976. "The role of background flow variations in stratified flows over topography". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35632.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaves 89-91).
As the atmosphere and oceans feature density variations with depth, the flow of a density-stratified fluid over topography is central to various geophysical and meteorological applications and has been studied extensively. For reasons of convenience and mathematical tractability, the majority of theoretical treatments of stratified flow over a finite-amplitude obstacle assume idealized background flow conditions, namely constant free-stream velocity and either a homogeneous or two-layer buoyancy-frequency profile. In this work, a numerical model is developed that accounts for general variations in the buoyancy-frequency profile far upstream and the presence of unsteadiness in the free-stream velocity. The model employs a second-order projection method for solving the Euler equations for stratified flow over locally confined topography in a horizontally and vertically unbounded domain - the flow configuration most pertinent to atmospheric applications - combined with absorbing viscous layers at the upper and lateral boundaries of the computational domain. Using this model, a study is first made of the effect of variations in the buoyancy frequency on the generation of mountain gravity waves.
(cont.) Balloon measurements reveal that, apart from a sharp increase (roughly by a factor of 2) at the so-called tropopause, atmospheric buoyancy-frequency profiles often feature appreciable oscillations (typical wavelength 1-2 kni). It is found that such short-scale oscillatory variations can have a profound effect on mountain waves owing to a resonance mechanism that comes into play at certain wind speeds depending on the oscillation length scale. A simple linear model assuming small sinusoidal buoyancy-frequency oscillations suggests, and numerical simulations for more realistic flow conditions confirm, that the induced gravity-wave activity under resonant conditions is significantly increased above and upstream of the mountain, causing transient wave breaking (overturning), similarly to resonant flow of finite depth over topography. The effect of temporal variations in the free-stream velocity is then explored for a range of amplitudes and periods typical of those encountered in the field. The simulations reveal that transient disturbances resulting from such variations can be significant, particularly in the nonlinear regime, and steady states predicted on the assumption of uniform wind may not be attainable.
by Ivan Skopovi.
Ph.D.
14
Abrishami-Savjublagh, Yoseph. "Numerical computations of dispersed flow and gravity stratified two-phase flow". Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/47736.
Testo completo
15
Olvera, Cabrera Daniel. "Coherent structures in stably stratified plane couette flow". Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.723480.
Testo completo
16
Johnstone, Roderick. "Numerical simulation of stably stratified flow over hills". Thesis, University of Surrey, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364820.
Testo completo
17
Oglethorpe, Rosalind Leigh Frances. "Mixing in stably stratified turbulent Taylor-Couette flow". Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708399.
Testo completo
18
Kay, David J. "Mixing processes in a highly stratified tidal flow /". Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9639.
Testo completo
19
Klymak, Jody Michael. "Stratified flow and turbulence over an abrupt sill /". Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/10982.
Testo completo
20
Renaud, Antoine. "On wave-mean flow interactions in stratified fluid". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN059/document.
Testo completoAbstract (sommario):
La dynamique des écoulements géophysiques planétaires est fortement influencée par des processus physiques souvent non résolus par les modèles numériques de circulation générale. Il est essentiel de comprendre les mécanismes physiques sous-jacents pour paramétrer l’effet des petites échelles sur les grandes. Dans cette thèse, nous étudions un problème emblématique d’interactions entre ondes et écoulements moyens : la dynamique des écoulements zonaux forces par des ondes internes de gravite. Une manifestation remarquable de ces interactions est l’oscillation quasi-biennale (QBO) des vents équatoriaux dans l’atmosphère terrestre. Dans un premier temps, nous décrivons une transition vers le chaos dans un modèle quasi-linéaire classique du QBO. Nous montrons que ces bifurcations persistent dans des simulations numériques directes. A l’aune de ces résultats, nous proposons une interprétation de l’observation d’une rupture inattendue de la périodicité du QBO en 2016. Le mécanisme de génération d’écoulements moyens par les ondes dans les fluides stratifies nécessite la prise en compte d’effets dissipatifs. Il s’agit d’un phénomène analogue au "streaming" acoustique. Dans un second temps nous exploitons cette analogie en étudiant la génération d’écoulements moyens par les ondes internes proche d’une paroi, a l’aide d’approches asymptotiques multi échelles. Finalement, nous proposons une approche inertielle pour décrire l’émergence spontanée d’écoulements vorticaux en présence d’ondes : nous appliquons les outils de mécanique statistique pour calculer la partition d’énergie entre petites et grandes échelles dans le modèle d’eau peu profondeThe dynamics of planetary-scale geophysical flows is strongly influenced by physicalprocesses, mostly unresolved by general circulation numerical models. To parametrisethe coupling between small and large scales, it is essential to understand the underlying physical mechanisms. In this thesis, we study an emblematic problem of interactions between waves and mean flows: the dynamics of zonal flows forced by internal gravity waves. A striking manifestation of these interactions is the quasi-biennial oscillation (QBO) of equatorial winds in the Earth’s atmosphere. First, we describe a transition to chaos in a classical quasilinear model of the QBO and show that these bifurcations persist in direct numerical simulations. Based on these results, we suggest an interpretation for the observation of the unexpected periodicity disruption of the QBO in 2016. The mechanism by which mean flows are generated by waves in stratified fluids requires the consideration of dissipative effects. This phenomenon is analogous to acoustic "streaming". In a second time, we exploit this analogy to study the generation of mean flows by internal gravity waves close to a wall, using multi-scale asymptotic approaches. Finally, we propose an inertial approach to describe the spontaneous emergence of vortical flows in the presence of waves: we apply the tools of statistical mechanics to calculate the partition of energy between small and large scales in the shallow-water model
21
Hughes, Graham Owen. "Aspects of mixing in stratified flows". Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324969.
Testo completo
22
Holmes, Damian J. "Gravity waves in uniform windflow over topography". Thesis, University of Surrey, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336449.
Testo completo
23
Khor, Siew Hiang. "Three-phase liquid-liquid-gas stratified flow in pipelines". Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8714.
Testo completo
24
薛明輝 e Ming-fai Sit. "Computation of stratified flow past three dimensional surface mounted obstacles". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1988. http://hub.hku.hk/bib/B31208897.
Testo completo
25
梁偉文 e Wai-Man Leung. "Computational studies on the motion of a stratified fluid". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31226346.
Testo completo
26
Leung, Wai-Man. "Computational studies on the motion of a stratified fluid /". Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23589504.
Testo completo
27
Issaev, Vassili. "Turbulent mixing in temporally evolving stratified channel flow, an investigation through direct numerical simulations". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29903.
Testo completoAbstract (sommario):
Turbulent flows affected by stable density stratification occur ubiquitously in wide range of geophysical
and environmental flows such as the ocean, the atmosphere or rivers and lakes. Within such flows the
process of turbulent mixing plays a leading order role in numerous physical and ecological processes
such as the vertical transport of heat, salt and nutrients as well as being vital to accurately predict
global energy circulation models. A better understanding of the flow dynamics and the mechanisms
that govern turbulent mixing as well as its accurate prediction in stratified flows is therefore crucial to
accurately resolve such processes. If stratified flow is constrained by physical boundaries perpendicular
to the gravitational vector, then the flow develops into a distinctly vertically inhomogeneous state
that adds an additional layer of complexity into the mixing dynamics of the flow. Motivated by
the stratified river flows of Australia, this thesis aims to enhance our knowledge and understanding
of turbulent mixing in vertically inhomogeneous stratified flows through an extensive set of direct
numerical simulations (DNS) of stratified channel flow.
By performing a canonical ‘sunrise’ DNS of initially isothermal turbulent channel flow subject to
sudden radiative heating we demonstrate that the flow undergoes an initial ‘rapid’ suppression of
turbulence due the reduction of the fluctuating vertical velocity component w′ from the sudden introduction
of stable stratification. The flow ‘slowly’ recovers towards a stationary state as the flow
accelerates and the mean shear develops such that equilibrium is achieved in the turbulent kinetic energy
and momentum flux balances. We demonstrate that for the temporally evolving flow, the global
suppression of turbulent mixing defined by bulk measures of the eddy diffusivity and viscosity is well
predicted by the mixed bulk parameter Ri−1
τ Reτ , where Riτ and Reτ are the friction Richardson
and Reynolds numbers respectively such that mixing within the flow becomes strongly suppressed for
Ri−1
τ Reτ ≲ 10 and approaches neutral conditions for Ri−1
τ Reτ ≳ 100. We find that the convergence of
the flow towards stationarity is a globally parabolic process such that the flow at all depths simultaneously
obtains equilibrium in the buoyancy and momentum fluxes. Scaling arguments are presented
to demonstrate that this process may be parameterized through bulk flow properties such that the
flow achieves equilibrium at Ri−1/2
τ (t/Tτ ) ≈ 2 provided that Ri−1
τ Reτ ≲ 100, where t is the measured
time from its initial isothermal state and Tτ is the bulk friction time scale. We propose that the bulk
scaling presented could lend itself as a useful forecasting tool for the onset of suppressed mixing in
real stratified river flows.
By considering instantaneous horizontal planar averages of the temporally evolving flow we observe
three distinctly different mixing regimes separated by transitional values of turbulent Froude number
Fr: a weakly stratified regime for Fr > 1, an intermediate regime for 0.3 < Fr < 1 and a saturated
regime for Fr < 0.3. The mixing coefficient Γ is well predicted by the parametrization schemes of
Maffioli et al. (2016) and Garanaik and Venayagamoorthy (2019) across all three regimes through
instantaneous measurements of Fr and the ratio LE/LO, where LE and LO are the Ellison and
Ozmidov length scales respectively. The flux Richardon number Rf shows linear dependence on the
gradient Richardson number Rig up to a transitional value of Rig = 0.25 past which it saturates again
to a constant value independent of Fr or Rig. By examining the flow as a balance of inertial, shear
and buoyancy forces, we derive physically based scaling relationships to demonstrate that Rig ∼ Fr−2
and Rig ∼ Fr−1 in the weakly and moderately stratified regimes and that Rig becomes independent
of Fr in the saturated regime. Our scaling analysis and results suggest that an extended range of
the LE/LO ∼ Fr−1 scaling of Garanaik and Venayagamoorthy (2019) in the intermediate regime
manifests due to the influence of mean shear. Hence we directly reconcile the Fr,Rig and LE/LO
frameworks across all three mixing regimes for our shear driven flow.
By adapting the density inversion criterion method of Portwood et al. (2016) for our flow, we demon-
1
strate that the flow may be robustly separated into regions of active turbulence for which ReB ≳ O(10)
and quiescent fluid where ReB ≲ O(10), where ReB is the buoyancy Reynolds number. The intermittency
in the surface heated channel flow spontaneously manifests as a deformed horizontal interface
between the upper quiescent and lower turbulent flow. We find the region just below the interface is
characterized by vigorous and efficient energetic mixing from Kelvin-Helmholtz type overturning instabilities,
with the thickness of the interfacial layer being proportional to the Ellison length LE. The
resulting vertical intermittency profile quantified through a depth varying turbulent volume fraction
is accurately predicted by a local Monin-Obukhov length normalized in viscous wall units Λ+ such
that the flow begins to display intermittency within the parameter range of 2.5 ≲ Λ+ ≲ 260. We
find the ‘turbulent’ flow within this region to be described by constant critical gradient Richardson
and turbulent Froude numbers of Rig,c ≈ 0.2, Frc ≈ 0.3 and Γc ≈ 0.25, suggesting that for our flow,
critical mixing conditions arise from the intermittency resulting from stratification. By considering
conditional averages of both the ‘turbulent’ and ‘quiescent’ flow separately within this critical regime,
we find that the ‘turbulent’ flow continues to display a Γ ∼ Fr−1 relationship in the limit of Fr < Frc,
while the quiescent flow shows no correlation between Γ and Fr. We demonstrate that for stratified
open channel flow, the emergence of an asymptotic ‘saturated’ Γ regime in the limit of a low ‘global’
Fr occurs directly due to intermittency and increasing contributions to measurements of Γ from the
quiescent flow.
28
Khallahle, Jack Buckhill. "Numerical Simulation of Flow Parameters in Stratified Gas-Liquid Flow in a Horizontal Pipe". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29931.
Testo completoAbstract (sommario):
The transportation of gas-liquid mixtures in horizontal pipes as two-phase stratified flow is examined using computational fluid dynamics (CFD) method. The design of these pipelines requires accurate prediction of flow parameters such as pressure drop and liquid holdup. Many empirical correlations have been developed in the last 70 years and are well documented in the literature to obtain these parameters using experimental, analytical and numerical methods.
In this investigation, the numerical method based on CFD code-FLUENT is used as an alternative to the experimental method to obtained numerical data such as gas wall shear stress, liquid holdup and pressure drop in order to calculate interfacial shear stress using semi-mechanistic flow model for stratified-smooth and stratified-wavy flow based on the 3D CFD models developed in FLUENT DesignModeler. The Volume of Fluid (VOF) model and k-ω SST turbulence model were used to obtain numerical data from the CFD models for validations.
In the 3D CFD model for gas flow over stationary liquid surface, the average gas velocities and corresponding liquid heights from the experimental data were validated in the two-phase flow domain. The interfacial friction factor correlation proposed was in good agreement against the existing two-phase friction factors using conventional two-phase flow calculation method, while the mathematical formulations involving hydrostatic force for the interfacial and gas wall shear stresses were poorly correlated against existing correlations.
In the co-current gas-liquid flow 3D CFD model, the pressure drop, gas wall shear stress, interfacial shear stress and liquid holdups were in excellent agreement and the interfacial friction factor correlations proposed were in good agreement with the published correlations. The flow patterns were correctly predicted as stratified-smooth and wavy flow on the flow map.
A design procedure involving both 3D CFD models was proposed and presented in Appendix D.
29
Davies, Wykes Megan Sydney. "Efficient mixing in stratified flows : Rayleigh-Taylor instability within an otherwise stable stratification". Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708349.
Testo completo
30
Omgba-Essama, C. "Numerical modelling of transient gas-liquid flows (application to stratified & slug flow regimes)". Thesis, Cranfield University, 2004. http://hdl.handle.net/1826/1057.
Testo completoAbstract (sommario):
A new methodology was developed for the numerical simulation of transient two-phase
flow in pipes. The method combines high-resolution numerical solvers and adaptive mesh
refinement (AMR) techniques, and can achieve an order of magnitude improvement in
computational time compared to solvers using conventional uniform grids.
After a thorough analysis of the mathematical models used to describe the complex
behaviour of two-phase flows, the methodology was used with three specific models in
order to evaluate the robustness and accuracy of the numerical schemes developed, and to
assess the ability of these models to predict two physical flow regimes, namely stratified
and slug flows.
The first stage of the validation work was to examine the physical correlations required for
an accurate modelling of the stratified smooth and wavy flow patterns, and a new
combination of existing correlations for the wall and interfacial friction factors was
suggested in order to properly predict the flow features of the experimental transient case
investigated.
The second and final phase of the work dealt with the complex and multi-dimensional
nature of slug flow. This flow regime remains a major and expensive headache for oil
producers, due to its unsteady nature and high-pressure drop. The irregular flow results in
poor oil/water separation, limits production and can cause flaring. The modelling
approached that was adopted here is based on the two-fluid model, which can theoretically
follows each formed slug and predicts its evolution, growth and decay, as it moves along
the pipe.
However, the slug flow study, performed here through a test case above the Inviscid
Kelvin-Helmholtz transition from stratified to slug flow, showed that the incompressible
two-fluid model used is unable to accurately predict most of the features of this complex
flow. Mechanisms such as the interfacial wave formation, the slug growth and propagation,
although observed from the simulations, cannot be accurately determined by the model.
31
Brown, Harmony Rose. "Numerical simulations of stratified fluid flow over topography near resonance". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p1450159.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed Mar. 25, 2008). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 83-85).
32
Davis, Kevin S. (Kevin Scott) 1975. "Flow of nonuniformly stratified fluid of large depth over topography". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9409.
Testo completo
33
Epifanio, Craig Charles. "High-drag states and lee vortices in stratified flow over topography /". Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/10072.
Testo completo
34
Walker, Sharon Amanda. "The effect of time on interfacial mixing in density stratified flows". Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361235.
Testo completo
35
Roberts, Ian Frank. "Modelling and experimental studies of transient stratified multiphase flows". Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/7433.
Testo completo
36
Al-Gheithy, Ali Amor. "Modelling of transient flow and pressure behaviour in multilayer stratified reservoirs". Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261209.
Testo completo
37
SILVA, ALBERTO MILONE. "EXPERIMENTAL RESULTS OF INTERFACIAL SHEAR STRESS IN STRATIFIED GAS-LIQUID FLOW". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1991. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19314@1.
Testo completoAbstract (sommario):
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO presente trabalho analisa experimentalmente o escoamento estratificado gás-líquido (ar-água) em um duto de seção retangular. Obteve-se uma correlação empírica para a tensão de cisalhamento na interface. Verifica-se que tal tensão, além de ser função dos números de Reynolds de ambos os escoamentos, depende também de características inerentes à fase líquida. Um perfil teórico de velocidade do gás foi comparado com os dados experimentais obtidos por anemometria para a região logarítmica. Foi realizada uma análise de incertezas, que mostrou uma elevada confiabilidade nos resultados obtidos.
Experiments were carried out to analyse a gás-liquid (air-water) stratified flow through a retangular duct. An empirical correlation was ontained for the shear stress at the interface. Such shear stress, that depends on the Reynolds numbers of both flows, is also a function of liquid specific parameters. A theoretical gas velocity profile was compared with experimental data using a hot-wire anemometry with good results in the logaritimic region. The uncertainly abalysis shows that this correlation presents a very low degree of uncertainly.
38
Podber, David P. "Modeling strongly stratified flow using the dynamic grid adaptation (DGA) technique /". The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487946776024051.
Testo completo
39
Musiak, Jeffery Daniel. "Three-dimensional circulation dynamics of along-channel flow in stratified estuaries /". Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/6823.
Testo completo
40
Lu, Zhiming. "Numerical simulation of internal waves in stratified fluid flow over topography". Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/35028.
Testo completoAbstract (sommario):
The main purpose of this thesis is to investigate internal solitary wave generation and evolution in density-stratified fluid flows over both two-dimensional and three-dimensional bottom topographies using mainly numerical methods supported by some theoretical results. The numerical scheme to solve the forced KdV, KPII and KPI equation is a combination of the Runge–Kutta and Crank–Nicholson methods; a pseudo-spectral method is used to solve the two-dimensional fully nonlinear Euler equations in the streamfunction-vorticity form. The numerical results for a stratified flow over a two-dimensional step or an obstacle show that, in the resonant region, a forward step mainly generates upstream-advancing waves, while a backward step mainly generates downstream-propagating waves (a depression followed by lee waves), so the waves generated by a localised positive obstacle can be regarded as a simple superposition of the waves generated by its fore part and aft part. In contrast, the waves generated by a negative obstacle are quite different due to the nonlinear interaction between waves generated by its fore part and aft part.
41
Aigner, Andreas 1972. "Numerical simulations of internal and inertial solitary waves". Monash University, Dept. of Mathematics and Statistics, 2001. http://arrow.monash.edu.au/hdl/1959.1/8880.
Testo completo
42
Zhou, Jingnan. "Numerical studies of stably stratified planetary boundary-layer flows over topography and their parameterization for large scale numerical model". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq27395.pdf.
Testo completo
43
Akiyama, Shinsaku. "Measurement of the flow past a sphere descending at a constant speed in a salt stratified fluid". Kyoto University, 2018. http://hdl.handle.net/2433/235086.
Testo completo
44
Mathews, Tobias John. "Void structure, colloid and tracer transport properties of stratified porous media". Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/2794.
Testo completoAbstract (sommario):
The characterisation of the properties of porous materials is of great importance in the effective management of natural and manmade systems. A sophisticated network model, 'Pore-Cor', of some of these properties has been previously developed. The present study has significantly extended the scope of the model's predictive capabilities. Flow and transport behaviour was examined in laboratory sand columns of various depths. These experiments examined unsaturated flow of water and conservative solute tracer transport through homogeneous sand samples. Flow through these was not homogeneous or repeatable. Experimental observations found that this may have been due to subtle random variations in packing, and the network model was shown to be able to simulate these. Solute transport of bromide was studied, applied both uniformly and from a point source. Both scenarios were modelled using a convection-dispersion equation, and it was demonstrated that the lateral component of such transport was highly significant. It was shown how convection-dispersion equation predictions of uniformly applied tracer transport might be improved by the application of the network model and a method for improving predicted lateral solute transport was outlined. It has been shown that levels of correlation in the distribution of differently sized voids within porous material may be responsible for large variations in permeability. This can make accurate modelling of permeability very difficult. A technique was developed for assessing the degree and nature of such correlations. The new method was tested on a variety of artificial and real samples and demonstrated to provide a quantitative assessment of such correlations. A method by which this could be used to improve network model simulations of materials possessing such correlation was described.
45
Badeau, Allen E. "A droplet formation and entrainment model for stratified liquid-liquid flows". Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1737.
Testo completoAbstract (sommario):
Thesis (M.S.)--West Virginia University, 2000.Title from document title page. Document formatted into pages; contains xiii, 150 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 140-144).
46
Bambrey, Ross R. "Strong interactions between two co-rotating vortices in rotating and stratified flows /". St Andrews, 2007. http://hdl.handle.net/10023/341.
Testo completo
47
LIMA, HELENA ASSAF TEIXEIRA DE SOUZA MOTA. "FLOW SIMULATION OF MACRO-EMULSION FLOODING AT STRATIFIED RESERVOIRS CONSIDERING CAPILLARY EFFECTS". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=28384@1.
Testo completoAbstract (sommario):
PETRÓLEO BRASILEIRO S. A.O aumento do fator de recuperação e o uso de métodos de recuperação avançada no atual cenário de novos patamares de preços representam um enorme desafio para a indústria do petróleo. Neste contexto, o uso de emulsões óleo-água como um método de recuperação avançada torna-se bastante atrativo. Diversos trabalhos mostraram um aumento no volume de óleo produzido através da injeção de emulsões óleo-água. Resultados de pesquisas experimentais indicam que a injeção de emulsões pode ser utilizada como agente de controle de mobilidade, bem como reduzindo a saturação residual de óleo. A aplicação do método de injeção alternada água-emulsão-água (WAE) requer o entendimento do escoamento de emulsões no meio poroso e dos mecanismos responsáveis pela melhora na recuperação. Este entendimento tanto na escala de poros como na escala de reservatórios permite incorporação destes mecanismos na modelagem para simulação de fluxo de reservatórios. No presente trabalho foi feita a incorporação dos efeitos gravitacionais no modelo desenvolvido para o escoamento de emulsões em meios porosos através da parametrização das curvas de permeabilidade relativa em função da concentração de gotas e do Número de Capilaridade. O processo WAE foi avaliado através de simulações em duas e três dimensões (2D/3D) utilizando um conjunto de camadas do segundo modelo comparativo do SPE10. Com simulações 2D e 3D foi possível realizar um estudo de sensibilidade do processo em relação ao momento da injeção de emulsão, o tamanho do banco, e as faixas de vazão e respectivos números de capilaridades de atuação da emulsão.
In the current crude oil price scenario, the increase in oil recovery factor and the use of enhanced recovery methods represent a major challenge for the Oil Industry. In this context, the use of oil-water emulsion flooding as an enhanced recovery method becomes very attractive. Several studies have shown a significant potential to increase oil volume recovery by the injection of oil-water emulsions. Experimental results indicate that the emulsions injection can be used as a mobility control agent, resulting in a more uniform fluid displacement in the reservoir and lower residual oil saturation. Based on these experimental results, the most relevant parameters for emulsion injection performance effectiveness are droplet size, the local concentration of the dispersed phase of the emulsion and the local capillary number. The application of water alternating emulsion injection (WAE) method requires understanding of the flow of emulsions in porous media and the mechanisms responsible for the improved recovery. The understanding of this process in both porous scale and reservoir scale is fundamental to model emulsion injection effects in reservoir flow simulation. In this work, the gravitational effects was incorporated in the macroscopic model to represent flow of emulsions in porous media by relative permeability curves parametrization as function of emulsion concentration and of the local capillary number. The WAE process was evaluated in two and three dimensional simulations (2D / 3D) using a set of layers of the second SPE 10 comparative model. With 2D and 3D simulations, it was possible to explore a WAE injection performance sensitivity analysis considering the time at which the emulsion injection is started, the size of emulsion bank, and the injection flow rates and consequently the flow their capillary number.
48
CAMPOS, DEIBI ERIC GARCÍA. "STUDY OF INSTABILITY OF INTERFACIAL WAVES IN STRATIFIED LAMINAR-LAMINAR CHANNEL FLOW". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34760@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
AGÊNCIA NACIONAL DE PETRÓLEO
PROGRAMA DE EXCELENCIA ACADEMICA
No presente trabalho estudou-se numericamente a instabilidade das ondas na interface do escoamento estratificado de água e óleo em um canal plano. Esse padrão de escoamento, associado ao estágio inicial da formação de golfada, é comum em aplicações industriais, de áreas como produção de petróleo, nuclear, química e muitas outras. Através da introdução de perturbações controladas na interface do escoamento estratificado, analisou-se a evolução dessas perturbações à luz das teorias de estabilidade hidrodinâmica. Os experimentos numéricos foram realizados utilizando o método de Volume of Fluid (VOF) do simulador comercial ANSYS Fluent versão 15.0. Analisou-se o comportamento do escoamento em dois regimes distintos com relação a amplitude das ondas interfaciais. No primeiro regime, empregaram-se ondas pequenas o suficiente para que efeitos não lineares fossem desprezíveis. Os resultados obtidos apresentaram boa concordância com as previsões fornecidas por um solver das equações de Orr-Sommerfeld, para escoamento bifásico estratificado em um canal, indicando que a ferramenta numérica foi capaz de reproduzir o comportamento das ondas interfaciais. Mostrou-se que existe uma faixa de amplitudes, em torno de 0,2 porcento da altura do canal, a partir da qual os efeitos não lineares se tornam relevantes. No regime não linear foram avaliados diferentes cenários de interação não linear entre ondas, os quais geralmente são associados a transição do regime do escoamento estratificado para golfadas. Identificou-se o cenário mais relevante, analisando-se,a eficiência de cada uma dessas interações isoladamente. Observou-se que interações não lineares entre ondas de comprimento parecido são as que crescem mais rapidamente. Esse mecanismo parece ser dominante também na presença de um grande número de ondas, como é o caso esperado em um evento natural. Utilizou-se um modelo fracamente não linear, baseado nas equações de Stuart-Landau, para modelar o comportamento das ondas no escoamento, obtendo-se excelente concordância com os resultados das simulações. Isso é interessante do ponto de vista prático, pois sugere que modelos não lineares simples, como é o caso da equação de Stuart-Landau, podem ser implementados para melhorar as ferramentas utilizadas para prever mudanças de regime em escoamentos bifásicos.
In the present work, the instability of waves at the interface of the stratified flow of water and oil in a plane channel was numerically studied. This flow pattern, which is associated with the initial stages of slug formation, is common in industrial application in areas such as oil production, nuclear, chemical and many others. Through the introduction of controlled perturbations at the interface of a stratified flow, the evolution of the perturbations was analyzed based on hydrodynamics stability theories. Numerical experiments were performed using the Volume of Fluid (VOF) method of the ANSYS Fluent release 15.0 commercial simulator. The behavior of the flow in two different regimes with respect to the amplitude of the interfacial waves was analyzed. In the first regime, small enough waves were employed so that non-linear effects were negligible. The results obtained presented good agreement with the predictions provided by a solver of the Orr-Sommerfeld equations for stratified two-phase flow in a channel, indicating that the numerical tool was able to reproduce the behavior of the interfacial waves. It was shown that there is a range of amplitudes, around 0.2 per cent of the channel height, above which the non-linear effects become relevant. In the nonlinear regime, different scenarios of nonlinear interaction between waves, which are usually associated with transition from stratified flow pattern to slug flow, were evaluated. The most relevant scenario was identified, based on the efficiency of each independent interaction. It was observed that non-linear interactions between waves of similar length present the fastest growth. This mechanism seems to be dominant also in the presence of a large number of waves, as present in natural events. A weakly nonlinear model, based on the Stuart- Landau equations, was employed to model the wave behavior in the flow, obtaining an excellent agreement with the results of the simulations. This is interesting from a practical point of view, since it suggests that simple nonlinear models, such as the Stuart-Landau equation, can be implemented to improve the tools used to predict regime changes in two-phase flows.
49
Lim, Kahn Yung 1976. "Trapped disturbances and effects of tropopause height in stratified flow over topography". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/89314.
Testo completo
50
Nguyen, Duy. "An Investigation Of The Effect Of Meanders On Thermally Stratified Riverine Flow". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29567.
Testo completoAbstract (sommario):
This thesis describes the influences of meander geometrics on thermally stratified open-channel flow. Results of this study contribute toward a greater understanding of the physical characteristics of flow in riverine environments.
The presence of thermal stratification due to short-wave solar heating from above inhibits mixing, resulting in oxygen stratification and accumulation of contaminants and nutrients - conditions that have been found to cause long-term damage to the ecosystems. Reduced flow rates can also lead to acute damage events such as cyanobacterial outbreaks and mass fish kills. These conditions are progressively found in nature, linearly with the recent changing in climate and global warming. Topography, precisely the geometrical aspect, is one crucial factor that influences the evolution of thermal stratification in natural rivers. Hence, it is essential to investigate the effect of geometrical parameters on the thermally stratified flow.
Direct Numerical Simulation results for turbulent open-channel flow through idealized meanders with and without an internal heat source are used to investigate these effects.
The computational domain was meshed using an orthogonal, curvilinear coordinate system with velocity represented using physical components on a staggered grid arrangement.
For a very sharp meander, a comparison between stratified and neutral flows is carried out to investigate the distribution of secondary circulations, temperature field, vortices, and turbulence characteristics.
Five different channel curvatures at a moderate sinuosity are then used to investigate the effect of curvature on the flow features, stratification, mixing, and the energy transfers between the global potential and kinetic energy reservoirs.
Finally, simulation results of neutral and stratified flows at four different channel sinuosities at a moderate curvature are presented to explore the effects of meander geometry on the flow separation and boundary shear stress.