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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Experimental and Numerical Modelling of Submerged Hydraulic Jumps at Low-Head Dams

Lopez Egea, Marta January 2015 (has links)
This study, which includes both experimental and numerical-modelling components, investigates the potentially dangerous conditions that can often occur when low-head dams (or weirs) are overtopped and ‘submerged’-type hydraulic jumps subsequently form downstream of them. The combination of high local turbulence levels, air entrainment, and strong surface currents associated with submerged jumps pose a significant risk to safety of boaters and swimmers. In this study, a wide range of flow regimes and different experimental conditions (i.e. crest length and downstream apron elevation) were considered. The experimental phase involved physical model testing to determine: (i) the hydraulic conditions that govern submerged jump formation, and (ii) the hydrodynamic characteristics of the submerged vortex. The numerical model, developed using OpenFOAM, was validated with the obtained experimental data. This research seeks to help develop improved guidelines for the design and safe operation of low-head dams. The experimental phase of the study involved physical model testing to determine: (i) the hydraulic conditions that govern submerged jump formation, and (ii) the hydrodynamic characteristics of the submerged vortex. The numerical modelling work involved using interFoam (OpenFOAM toolbox) for simulating the experimental results. InterFoam is an Eulerian 3-D solver for multiphase incompressible fluids that employs the Volume of Fluid approach (VOF) to capture the water-air interface. The developed numerical model was subsequently validated using the experimental data collected and processed by the author of this study. The range of tailwater depths associated with submerged hydraulic jump formation is dramatically reduced when a broad-crested weir is coupled with an elevated downstream apron, especially under high flow rate conditions. However sharp-crested weirs induced vortices which displayed reduced velocities and decreased spatial development, which were judged to be safer than broad crest lengths under the same discharge conditions. The classical formulation for the degree of submergence was not explicative when used to evaluate “how submerged the vortex was”. Consequently, a new normalized formulation which compares the local tailwater depth to the lower and upper tailwater limits for the submerged hydraulic jump is proposed. The numerical model developed for this study demonstrated the existence of residual turbulent kinetic energy at downstream sections located within the vortex’s extension, at instants coinciding with the presence of a fully formed roller. This turbulent energy is arguably responsible for the stationary nature of the vortex under constant flow conditions. Residual vertical and horizontal velocities at points located within the vortex’s domain are indicative of the existence of the free surface current.
82

Numerical Modelling of Extreme Hydrodynamic Loading on Coastal Structures

Sarjamee, Samieh January 2016 (has links)
Natural disasters usually occur without any warning. They can leave trail of destruction and cause much tragedy. We are at a time when we witness fast technological advances; hence, we need to apply the force of scientific advancements to decrease economic losses and the number of human deaths. Tsunami is one of the extreme environmental events that leaves nothing but a path of death and destruction, and as a result, it is essential to understand this phenomenon and identify the mitigation strategies. Several mitigation strategies have been proposed so far; however, more investigations are still required to achieve an acceptable solution. Researchers around the world are studying different aspects of this phenomenon. One of the proposed solutions that has received much attention is designing tsunami-resistant structures which can withstand the force of a tsunami bore. Various studies have been done so far to understand the base shear force of tsunami bore on structures. The focus of this thesis is to improve and better understand the characteristics of the tsunami base shear forces on structures. Hence, in this thesis, two numerical studies were proposed and performed with the main goal of estimating the total tsunami forces on structure under two different conditions. Those include structures with various cross sections, as well as positioning a mitigation wall at an appropriate location relative to the structure. The first study focused on developing a numerical model to study the relationship between tsunami forces and the geometry of the structure. The main goal of this study was to define a numerical model capable of simulating this case precisely. To ensure the accuracy of the model, a comparison was carried out between the results of the numerical model and experimental test performed at the NRC-CHC (National Research Council- Canadian Hydraulics Center) laboratory in Ottawa, Canada and Université Catholique de Louvain (UCL), Belgium, which revealed a very good agreement between the results of the experimental test and numerical model. Further, the validated model was applied to investigate the tsunami force on structures with various cross sections. The second study focus was on developing a numerical model for understanding the role of mitigation wall (a novel idea proposed as a mitigation strategy by the second author of technical paper 2) on reducing the exerted force of tsunami on structures. After developing various models and applying several turbulence models, a valuable result was obtained which demonstrated that a Large Eddy Simulation (LES) model seems to be an excellent approach for predicting the tsunami forces on the structure with a mitigation wall in the direction of the flow. The results of this study will be used to better estimate the tsunami forces exerted on coastal structures which will light the path to the main goal of designing tsunami resistant-structures.
83

Numerical Modeling of Extreme Flow Impacts on Structures

Asadollahi Shahbaboli, Nora January 2016 (has links)
Recent tsunami disasters caused devastating damages to well-engineered coastal infrastructures. In fact, the current design guidelines are not able to provide realistic estimations of tsunami loads in order to design structures to withstand tsunamis. Tsunami hydrodynamic forces are estimated using the drag coefficient. This coefficient is traditionally calculated based on a steady flow analogy. However, tsunami bores behave like unsteady flows. The present work aims at investigating the tsunami forces for different structure geometries to provide realistic guidelines to estimate drag coefficients considering unsteady flows. In the present paper, the dam-break approach is used to investigate the tsunami-like bore interaction with structures. A three-dimensional multiphase numerical model is implemented to study the tsunami induced forces on rectangular shape structures with various aspect ratios (width/depth) and orientations. The numerical model results are validated using measured forces and bore surface elevations of the physical experiments. A scaled-up domain is modeled in order to eliminate the effects of domain sidewalls in the simulation results. The drag coefficient relations with structure geometries and bore depths are provided. The obtained hydrodynamic forces and drag coefficients are compared with existing data in the literature and design codes. For the second topic, a multi-phase three-dimensional numerical reproduction of a large scale laboratory experiment of tsunami-like bores interaction with a surface-piercing circular column is presented. The numerical simulation is conducted in OpenFOAM. The dam-break mechanism is implemented in order to generate tsunami-like bores. The numerical model is validated using the experimental results performed at Canadian Hydraulics Center of the National Research Council (NRC-CHC) in Ottawa. The unsteady Reynolds Averaged Navier-Stokes equations (RANS) are used in order to treat the turbulence effects. The Shear Stress Transport (SST) k-ω turbulence model showed high level of accuracy in replication of the bore-structure interaction. Further, a scaled-up domain is used to investigate the influence of the bed condition in terms of various downstream depths and roughness. Finally, a broad investigation on the bore propagation characteristics is performed. The resulting stream-wise forces exerted on the structural column as well as the bore velocity are compared and analyzed for smooth, rough, dry and wet beds with varying depths.
84

Estudio computacional de la influencia del levantamiento de aguja sobre el flujo interno y el fenómeno de la cavitación en toberas de inyección diésel

Martínez López, Jorge 30 May 2013 (has links)
Durante el proceso de apertura y cierre de un inyector Diesel, las características del combustible a la salida de la tobera cambian significativamente como consecuencia del movimiento de la aguja. Este hecho tiene una enorme influencia en el desarrollo del chorro y en el proceso de mezcla entre el aire y el combustible y, por tanto, en el posterior proceso de combustión. Sin embargo, y a pesar de su importancia, todavía hoy existen multitud de cuestiones sobre el proceso de inyección que permanecen sin resolver debido, en parte, a la dificultad para llevar a cabo experimentos a levantamientos de aguja parciales. Teniendo en cuenta lo anterior, la presente tesis se ha centrado en el estudio de la influencia del levantamiento de aguja sobre el flujo interno en toberas de inyección Diesel. Este trabajo se ha llevado a cabo mediante simulaciones tridimensionales del flujo en condiciones cavitantes y no cavitantes, modelando la cavitación mediante un modelo de equilibrio homogéneo implementado en OpenFOAM. Antes de analizar en profundidad la influencia de la posición de la aguja, el código ha sido puesto a punto y validado con resultados experimentales en un orificio calibrado, una tobera monorificio y una tobera multiorificio en condiciones de levantamiento de aguja máximo. El modelo de cavitación ha mostrado una gran precisión en la predicción del gasto másico, el flujo de cantidad de movimiento, la velocidad, los coeficientes de flujo y la apariencia de la cavitación. Además, los resultados computacionales y experimentales obtenidos en la validación del código han servido para estudiar alguno de los fenómenos asociados a la cavitación, como el colapso de gasto másico o el aumento de velocidad y de turbulencia. Tras la validación del código, éste ha sido utilizado para analizar la influencia del levantamiento de aguja en una tobera microsaco real. Inicialmente, se ha llevado a cabo un estudio de más de 500 ejecuciones simulando diferentes levantamientos de aguja fijos mediante métodos RANS. En este estudio, centrado principalmente en las características del combustible a la salida de la tobera y en el desarrollo de la cavitación, se ha podido observar un cambio significativo en el aspecto de la cavitación en función de la posición de la aguja: para levantamientos grandes, el vapor se desarrolla a lo largo de la parte superior del orificio, mientras que para levantamientos pequeños, la cavitación aparece en el asiento de la aguja y en la parte inferior del orificio para contrapresiones relativamente bajas. Este hecho tiene una enorme influencia sobre los valores de gasto másico, de flujo de cantidad de movimiento y de velocidad efectiva, los cuales apenas varían para levantamientos de aguja mayores de 75 ¿m. Posteriormente, los efectos del levantamiento de aguja han sido estudiados aplicando métodos LES. El uso de Large Eddy Simulation ha proporcionado información de gran relevancia sobre el flujo interno, especialmente sobre el desarrollo de la turbulencia y su interacción con el fenómeno de la cavitación. Los resultados de este estudio han demostrado que la cavitación favorece el desarrollo de la turbulencia, provocando un cambio notable de los niveles de turbulencia y de la región más turbulenta de la tobera en función de la posición de la aguja. Además, los resultados han puesto en evidencia la existencia de una cierta interacción o interdependencia entre ambos fenómenos, puesto que la turbulencia tiene a su vez importantes efectos sobre la apariencia de la cavitación. Profundizando en el desarrollo de la turbulencia, se ha observado también un aumento significativo del número de vórtices presentes en el fluido y un descenso de su tamaño a medida que la aguja desciende. Finalmente, se ha analizado la influencia del levantamiento de aguja mediante malla móvil, reproduciendo así el movimiento real de la aguja durante todo el proceso de inyección. Este último estudio ha sido posible gracias a la modificación del código y ha sido utilizado a partir de condiciones de contorno proporcionadas por un modelo unidimensional del inyector creado en AMESim. Por una parte, se han comparado los resultados obtenidos mediante simulaciones estacionarias y transitorias, mostrando diferencias despreciables en el cálculo de las características del combustible en la salida de los orificios de la tobera. No obstante, se ha detectado un menor volumen de combustible en fase vapor en las simulaciones transitorias, especialmente para pequeños levantamientos de aguja. Por otra parte, se ha comparado la tasa de inyección experimental con la tasa obtenida en OpenFOAM y AMESim. Dicha comparación ha permitido demostrar el gran potencial de AMESim y el buen comportamiento de OpenFOAM para predecir la tasa de inyección. / Martínez López, J. (2013). Estudio computacional de la influencia del levantamiento de aguja sobre el flujo interno y el fenómeno de la cavitación en toberas de inyección diésel [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29291 / TESIS
85

Implementation and Development of an Eulerian Spray Model for CFD simulations of diesel Sprays

Pandal Blanco, Adrián 01 September 2016 (has links)
[EN] The main objective of this work is the modeling of diesel sprays under engine conditions, including the atomization, transport and evaporation processes pivotal in the diesel spray formation and its development. For this purpose, an Eulerian single fluid model, embedded in a RANS environment, is implemented in the CFD platform OpenFOAM. The modeling approach implemented here is based on the ⅀-Y model. The model is founded on the assumption of flow scales separation. In actual injection systems, it can be assumed that the flow exiting the nozzle is operating at large Reynolds and Weber numbers and thus, it is possible to assume a separation of features such as mass transport (large scales) from the atomization process occurring at smaller scales. The liquid/gas mixture is treated as a pseudo-fluid with variable density and which flows with a single velocity field. Moreover, the mean geometry of the liquid structures can be characterized by modeling the mean surface area of the liquid-gas interphase per unit of volume. Additionally, an evaporation model has been developed around the particular characteristics of the current engine technologies. This means that vaporization process is limited by fuel-air mixing rate and fuel droplets evaporate as long as there is enough air for them to heat up and vaporize. Consequently, the evaporation model is based on the Locally Homogeneous Flow (LHF) approach. Under the assumption of an adiabatic mixing, in the liquid/vapor region, the spray is supposed to have a trend towards adiabatic saturation conditions and to determine this equilibrium between phases Raoult's ideal law is considered. Finally, the spray model is coupled with an advanced combustion model based on approximated diffusion flames (ADF), which reduces the computational effort especially for complex fuels and is a natural step for modeling diesel sprays. First, the model is applied to a basic external flow case under non-vaporizing conditions, extremely convenient due to both the experimental database available and the symmetric layout which allows important simplification of the modeling effort. Good agreement between computational results and experimental data is observed, which encourages its application to a more complex configuration. Secondly, the model is applied to the "Spray A" from the Engine Combustion Network (ECN), under non-vaporizing conditions, in order to reproduce the internal structure of diesel sprays as well as to produce accurate predictions of SMD droplets sizes. Finally, vaporizing "Spray A" studies are conducted together with the baseline reacting condition of this database. The calculated spray penetration, liquid length, spray velocities, ignition delay and lift-off length are compared with experimental data and analysed in detail. / [ES] El objetivo principal de este trabajo es el modelado de chorros diésel en condiciones de motor, incluyendo los fenómenos de atomización, transporte y evaporación fundamentales en la formación y desarrollo del chorro. Para este fin, se implementa un modelo de spray euleriano de tipo monofluido en un entorno RANS en la plataforma CFD OpenFOAM. El enfoque de modelado aplicado aquí sigue la idea de un modelo del tipo ⅀-Y. El modelo se fundamenta en la hipótesis de separación de escalas del flujo. En los sistemas de inyección actuales, es posible asumir que el flujo que sale de la tobera opera a altos números de Reynolds y Webber y por tanto, es posible considerar la independencia de fenómenos como el transporte de masa (grandes escalas del flujo) de los procesos de atomización que ocurren a escalas menores. La mezcla líquido/gas se trata como un pseudo-fluido con densidad variable y que fluye según un único campo de velocidad. Además, la geometría promedio de las estructuras de líquido se puede caracterizar mediante el modelado de la superficie de la interfase líquido/gas por unidad de volumen. Completando el modelo de chorro, se ha desarrollado un modelo de evaporación alrededor de las características particulares de las tecnologías actuales de los motores. Esto supone que el proceso de evaporación está controlado por mezcla aire-combustible y las gotas de combustible se evaporan siempre que exista suficiente aire para calentarlas y evaporarlas. Debido a esto, el modelo de evaporación implementado está basado en el enfoque de Flujos Localmente Homogéneos (LHF). Considerando una mezcla adiabática, en la región líquido/vapor, se supone que el chorro tiende a las condiciones adiabáticas de saturación y para determinar este equilibrio entre fases, se utiliza la ley ideal de Raoult. Finalmente, el modelo de chorro se acopla con un modelo avanzado de combustión basado en llamas de difusión aproximadas (ADF), que reduce el coste computacional especialmente para combustibles complejos y supone el paso lógico en el desarrollo del modelo para simular chorros diesel. En primer lugar, el modelo se aplica al cálculo de un caso básico de flujo externo no evaporativo, muy adecuado tanto por la extensa base de datos experimentales disponible como por la simetría geométrica que presenta, permitiendo una importante simplificación de la simulación. Los resultados obtenidos presentan un buen acuerdo con los experimentos, lo cual estimula su aplicación en configuraciones más complejas. En segundo lugar, el modelo se aplica al cálculo del "Spray A" del Engine Combustion Network (ECN), no evaporativo, para reproducir la estructura interna del chorro diesel así como predecir tamaños de gota (SMD) de forma precisa. Finalmente, se realizan estudios evaporativos del "Spray A" junto con la condición nominal reactiva de esta base de datos. La penetración de vapor, la longitud líquida, velocidad, el tiempo de retraso y la longitud de despegue de llama calculados se comparan con los datos experimentales y se analizan en detalle. / [CAT] L'objectiu principal d'aquest treball és el modelatge de dolls dièsel en condicions de motor, incloent els fenòmens d'atomització, transport i evaporació fonamentals en la formació i desenvolupament del doll. Amb aquesta finalitat, s'implementa un model de doll eulerià de tipus monofluid en un entorn RANS a la plataforma CFD OpenFOAM. L'enfocament de modelatge aplicat ací segueix la idea d'un model del tipus ⅀-Y. El model es fonamenta en la hipòtesi de separació d'escales del flux. En els sistemes d'injecció actuals, és possible assumir que el flux que surt de la tovera opera a alts nombres de Reynolds i Webber, i per tant és possible considerar la independència de fenòmens com el transport de massa (grans escales del flux) dels processos d'atomització que ocorren a escales menors. La mescla líquid / gas es tracta com un pseudo-fluid amb densitat variable i que flueix segons un únic camp de velocitat. A més, la geometria mitjana de les estructures de líquid es pot caracteritzar mitjançant el modelatge de la superfície de la interfase líquid / gas per unitat de volum. Completant el model, s'ha desenvolupat un model d'evaporació al voltant de les característiques particulars de les tecnologies actuals dels motors. Això suposa que el procés d'evaporació està controlat per la mescla aire-combustible i les gotes de combustible s'evaporen sempre que hi hagi suficient aire per escalfar i evaporar. A causa d'això, el model d'evaporació implementat està basat en el plantejament de fluxos Localment Homogenis (LHF). Considerant una mescla adiabàtica, a la regió líquid / vapor, se suposa que el doll tendeix a les condicions adiabàtiques de saturació i per determinar aquest equilibri entre fases, s'utilitza la llei ideal de Raoult. Finalment, el model de doll s'acobla amb un model avançat de combustió basat en flamelets de difusió aproximades (ADF), que redueix el cost computacional especialment per a combustibles complexos i suposa el pas lògic en el desenvolupament del model per simular dolls dièsel. En primer lloc, el model s'aplica al càlcul d'un cas bàsic de flux extern no evaporatiu, molt adequat tant per l'extensa base de dades experimentals disponible com per la simetria geomètrica que presenta, permetent una important simplificació de la simulació. Els resultats obtinguts presenten un bon acord amb els experiments, la qual cosa estimula la seva aplicació en configuracions més complexes. En segon lloc, el model s'aplica al càlcul del "Spray A" no evaporatiu de la xarxa Engine Combustion Network (ECN), per reproduir l'estructura interna del doll dièsel així com predir mides de gota (SMD) de forma precisa. Finalment, es realitzen estudis evaporatius del "Spray A" juntament amb la condició nominal reactiva d'aquesta base de dades. La penetració de vapor, la longitud líquida, velocitat, el temps de retard i la longitud d'enlairament de flama calculats es comparen amb les dades experimentals i s'analitzen en detall. / Pandal Blanco, A. (2016). Implementation and Development of an Eulerian Spray Model for CFD simulations of diesel Sprays [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/68490 / TESIS
86

Single-Phase Turbulent Enthalpy Transport

Shields, Bradley J 07 November 2014 (has links)
Vapor generation is central to the flow dynamics within fuel injector nozzles. Because the degree of atomization affects engine emissions and spray characteristics, quantification of phase change within diesel fuel injectors is a topic of design interest. Within the nozzle, the large pressure gradient between the upstream and downstream plena induce large velocities, creating separation and further pressure drop at the inlet corner. When local pressure in the throat drops below the fluid vapor pressure, phase change can occur with sufficient time. At the elevated temperatures present in diesel engines, this process can be dependent upon the degree of superheat, motivating the modeling of heat transfer from the wall. By modeling cavitation and flash boiling phenomena as a departure from equilibrium conditions, the HRMFoam model accurately reproduces canonical adiabatic flows. An experimentally determined relaxation time controls the rate at which vapor is generated, and includes model constants tuned for water and a diesel fuel surrogate. The model is shown to perform well for several benchmark experimental cases, including the work of Reitz, Lichtarowicz, and Nurick. With the implementation of the Farve-averaged energy equation, the present work examines and validates the transport of enthalpy through the fixed heat flux and fixed wall temperature boundary conditions. The pipe heat transfer experiments of Boelter and Allen are replicated using the kEpsilon, Realizable kEpsilon, and Spalart-Allmaras models. With proper turbulence model selection, Allen's heat transfer coefficient data is reproduced within 2.9%. Best-case bulk temperature rise prediction is within 0.05%. Boelter's bulk temperature rise is reproduced within 16.7%. Turbulent diffusivity is shown to determine radial enthalpy distribution.
87

CFD Study of Dense Effluent Discharges in Deep and Shallow Waters

Kheirkhah Gildeh, Hossein 29 November 2021 (has links)
Liquid wastes discharged from industrial outfalls have been researched for many years in the past. Majority of past studies, initiated in 1960s, were experimental studies mainly focused on basics of discharges such as key geometrical properties. Eventually, more robust experimental studies were performed to measure the mixing properties of effluent discharges with various jet configurations and ambient water conditions. Discharges could be as a means of submerged diffusers or surface channels and receiving water could vary from a homogenous calm ambient to a very complex stratified turbulent cross flow ambient. Depending on the bathymetric and economic situation around an outfall project, submerged discharges are preferred designs for most of ocean outfalls. It is the reason that majority of past studies have evaluated the mixing characteristics of submerged jets. Since early 1990s, the numerical modelling has emerged to support complex fluid mechanic problems. Later in 1990s and early in 2000s, the use of computational fluid dynamic (CFD) tools emerged in predicting the jet properties for the effluent discharges. Since then different numerical models have been developed for different applications. Similar to experimental studies, most of numerical studies have been focused on the submerged dense jet discharges. The current study intends to stay focused on the numerical modelling of such jets too; however, to cover the gaps in the literature. To achieve this, a thorough literature review was performed on the past CFD studies of over past 20 years to better understand what was done and what the gaps are. The results of this thorough review revealed that although there has been a great progress in the CFD studies in the field of effluent discharges, there are some applications that have not been investigated before, yet. It was found that there are some discharge inclinations that were not studied numerically before. Four discharge angles of 60°,75°, 80° and 85° were selected in this study, as previous studies mostly focused on 30° and 45°. The higher inclinations are more suitable for deep water outfalls where terminal rise height of the jet does not attach to the ambient water surface. The numerical model OpenFOAM was used in this study which is based on the Finite Volume Method (FVM) applying LRR turbulence model closure. LRR turbulence models was proved to be a capable choice for effluent discharge modelling. The second gap identified in the comprehensive literature review completed was the submerged dense effluent discharge into shallow water with surface attachment (for both inclined and vertical discharges). There was no previous numerical study of such jets identified. Three different regimes were identified: full submergence, plume contact and centerline impingement regimes (i.e. FSR, PCR and CIR). Key geometrical and dilution properties of these jets at surface contact (Xs, Ss) and return point (Xr, Sr) were extracted numerically and compared to those available from experiments. Two discharge angles (30° and 45°) were investigated based on the available experimental data. Five Reynolds-averaged Navier-Stokes (RANS) turbulence models were examined in this study: realizable k-ε and k-ω SST models (known as two-equation turbulence models), v2f (four equations to model anisotropic behavior) and LRR and SSG turbulence models (known as Reynolds stress models - six equations to model anisotropic behavior). Vertical dense effluent discharges are popular in the design of outfall systems. Vertical jets provide the opportunity to be efficient for a range of ambient currents, where the jet will be pushed away not to fall on itself. This research work investigates worst case scenario in terms of mixing and dilution of such jets: vertical dense effluent discharges with no ambient current and in shallow water where jet impacts the surface. This scenario provides a conservative design criteria for such outfall systems. The numerical modelling of such jets has not been studied before and this research work provides novel, though preliminary, insights in simulations of vertical dense effluent discharges in shallow waters. Turbulent vertical discharges with Froude numbers ranging from 9 to 24 were simulated using a Reynolds stress model (RSM), based on the results from inclined dense discharges to characterize the geometrical (i.e., maximum discharge rise Zm and lateral spread Rsp) and dilution μmin properties of such jets. Three flow regimes were reproduced numerically, based on the experimental data: deep, intermediate and impinging flow regimes.
88

Cavitation Induced by Rotation of Liquid / Cavitation Induced by Rotation of Liquid

Kozák, Jiří January 2020 (has links)
Tato disertační práce se zabývá experimentálním a numerickým výzkumem kavitace vyvolané rotací. Pro potřeby tohoto výzkumu byla využita transparentní osově symetrická Venturiho dýza, díky čemuž bylo možné zkoumat dynamiku kavitujícího proudění pomocí analýzy vysokorychlostních nahrávek.
89

Development and assessment of a one-dimensional CFD solver for boiling flows in bubbly regimes

Gómez-Zarzuela Quel, Consuelo 21 July 2020 (has links)
[EN] The present PhD thesis aims at the development of a one-dimensional solver capable of solving single- and two-phase flow fluid systems. The novelty of this project lies in the use of an open source CFD platform, called OpenFOAM, as a development framework for the new tool. For the new solver development, the conservation equations based on Navier- Stokes (three-dimensional system) have been analyzed and reduced to one dimension. For the two-phase simulations, the Two Fluid Model method was used as base. In addition, a series of empirical models have been selected as closing equations of the system. The final solver includes a series of requirements that reinforce their capabilities. Among them, the use of a second mesh that represents the solid and takes into account the heat transmitted to the fluid by conduction through a solid, stands out. On the other hand, the possible transfer of mass between phases in twophase fluids has been taken into account. Similarly, a subcooled boiling model has been implemented which takes into account the possible generation of vapor near the wall while the bulk is kept below saturation temperature. Finally, this paper presents the verification and validation of the solver. The verification has been carried out mainly with the system code TRACE, whose validation has been demonstrated in numerous works and its use is very extended in the scientific community. For the validation, we have the results of two experimental cases that allow us to demonstrate the physical validity of the new application developed. The use of this platform allows for a much more direct coupling between one- and three-dimensional domains, obtaining a better optimization of the calculation. / [ES] El presente trabajo de doctorado tiene por objetivo el desarrollo de un solver unidimensional capaz de resolver sistemas de fluidos monofásicos y bifásicos. La novedad de este proyecto reside en el uso de una plataforma CFD de código abierto, llamada OpenFOAM, como marco para el desarrollo de la nueva herramienta. Para el desarrollo del nuevo solver, se han analizado las ecuaciones de conservación basadas en Navier-Stokes (tridimensionales) y se han reducido a una dimensión. Para la parte bifásica del solver, se utiliza el método Two Fluid Model. Además, se han incluido todos los modelos empíricos necesarios como ecuaciones de cierre del sistema. El solver final incluye una serie de requerimientos que refuerzan sus capacidades. Entre ellas, destacan, por un lado, el uso de una segunda malla que represente el sólido y tenga en cuenta el calor transmitido al fluido por conducción a través de un sólido. Por otro lado, se ha tenido en cuenta la posible transferencia de masa entre fases en fluidos bifásicos. Igualmente, se ha implementado un modelo de ebullición subenfriada que tiene en cuenta la posible generación de vapor cerca de la pared mientras el centro del fluido se mantiene por debajo de la temperatura de saturación. Finalmente, este trabajo presenta la verificación y validación del solver. La verificación se ha realizado principalmente con el código de sistema TRACE. Para la validación, se cuenta con los resultados de dos casos experimentales que permiten demostrar la validez física de la nueva aplicación desarrollada. La implementación del nuevo solver en esta plataforma abierta permite un futuro acoplamiento mucho más directo entre mallas unidimensionales y tridimensionales, obteniendo una mayor optimización del cálculo. / [CA] El present treball de doctorat té per objectiu el desenvolupament d'un nou solver unidimensional capaç de solucionar sistemes amb fluids monofàsics i bifàsics. La novetat d'aquest projecte resideix en l'ús d'una plataforma CFD de codi obert, anomenada OpenFOAM com a marc de desenvolupament de la nova eina. Per al desenvolupament del nou solver, s'han analitzat les equacions de conservació basades en Navier-Stokes (tridimensionals) i s'han reduït a una dimensió. Per a la part bifàsica del solver s'utilitza el mètode Two Fluid Model. A més, s'han inclòs tots els models empírics necessaris com a equacions de tancament del sistema. El solver final inclou una sèrie de requeriments que reforcen les seues capacitats. Entre elles, destaquen, d'una banda, l'ús d'una segona malla que represente el sòlid i es tinga en compte la calor transmesa al fluid per conducció a través d'un sòlid. D'altra banda, s'ha tingut en compte la possible transferència de massa entre fases en fluids bifàsics. Igualment, s'ha implementat un model d'ebullició subrefredada que té en compte la possible generació de vapor prop de la paret mentre el centre del fluid es manté per davall de la temperatura de saturació. Finalment, aquest treball presenta la verificació i validació del solver. La verificació s'ha realitzat principalment amb el codi de sistema TRACE, la validació del qual s'ha demostrat en nombrosos treballs i el seu ús està molt estés en la comunitat científica. Per a la validació, es compta amb els resultats de dos casos experimentals que permeten demostrar la validesa física de la nova aplicació desenvolupada. L'ús d'esta plataforma permiteix un futur acoblament més directe, entre elements unidimensionals i tridimensionals, obtenint una major optimització del càlcul. / Gómez-Zarzuela Quel, C. (2020). Development and assessment of a one-dimensional CFD solver for boiling flows in bubbly regimes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/148368 / TESIS
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Direct Simulation of Two-Phase Flows in Porous Media using Volume-Of-Fluid (VOF) Method to Investigate Capillary Pressure-Saturation (Pc-Sw) Relation under Dynamic Flow Conditions

Konangi, Santosh January 2021 (has links)
No description available.

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