La modélisation des hydrosystèmes souterrains est devenue un outil crucial dans la gestion des ressources d'eaux souterraines ainsi que pour la surveillance des sites contaminés. L'objectif de ce travail de thèse est de modéliser l'écoulement d'une phase non-aqueuse liquide dense (DNAPL) dans les sols, et de développer un code pour la simulation des écoulements triphasiques de fluides incompressibles en milieux poreux. Le modèle mathématique pour les écoulements multiphasiques de fluides en milieux poreux est généralement constitué d'une équation de pression et de deux équations de saturation. Notre approche est fondée sur une formulation en pression globale : elle permet un découplage partiel des équations de pression et de saturations, et elle est plus efficace en termes de résolution numérique. Le nouveau modèle est discrétisé selon un schéma IMPES. Dans ce travail de thèse, la méthode des Eléments Finis Discontinus de Galerkine est combinée à un schéma de Godunov généralisé pour la résolution de la partie convective de l'équation de saturation. Un écoulement diphasique non miscible avec effets gravitaires importants et sans capillarité a été simulé. Une analyse fonctionnelle démontre que le profil de saturation de la phase non-aqueuse entrante dépend essentiellement du rapport de la vitesse totale sur la différence de densité entre la phase non aqueuse et l'eau. Le code développé a permis de simuler un drainage gravitaire à grande échelle. Enfin, un modèle numérique non-linéaire d'écoulement triphasique de fluides utilisant la Méthode des Lignes est introduit. Les causes d'oscillations instables du système en zone elliptique sont examinées. Des méthodes de relaxation et la construction d'un modèle de perméabilités relatives vérifiant la condition de Différentielle Totale sont envisagées. / Numerical simulation has become a crucial tool in addressing water-resource management and other environmental problems such as polluted sites monitoring. The aim of this work is to model the flow of a dense non aqueous phase liquid (DNAPL) in the subsurface by developing a numerical code to simulate three-phase (DNAPL, water, and gas), incompressible flow in porous media. The mathematical model for multiphase flow in porous media is generally composed of a system of one pressure and two saturation equations. Our approach is based on a global pressure model : it leads to a partial decoupling of the pressure and the saturation equation and is more efficient from the computational point of view. The new model is discretized by a Mixed Hybrid Finite Elements Method (MHFEM), Discontinuous Galerkin Finite Elements (DGFEM), IMPES resolution method. In this work, the DGFEM scheme is combined with a generalised Godunov scheme to solve the convective part of the saturation equation. An immiscible two-phase flow with predominant gravity effects and whithout capillary effects has been modelled. It has been shown that the saturation profile of a displacing non-aqueous phase liquid (NAPL) in an initially water-saturated porous medium depends strongly on the ratio between the total specific discharge and the density difference between the NAPL and water. The 2D-code enabled a simulation of a large-scale gravity drainage. Finally, a non-linear three-phase 1D flow formulation using Method of Lines (MOL) has been introduced. Unstable oscillatory behavior of the system when the initial state are in the elliptic region of the ternary diagram is examined. Non-equilibrium formulation and construction of relative permeability model satisfying the Total-Differential are foreseen.

<div>Vacuum is needed in many applications and, there are many types of pumps that can provide the vacuum level needed. One widely used pump is the liquid-ring vacuum pump, which does not involve any solid-solid contacts at interfaces where moving and stationary parts meet. Though liquid-ring vacuum pumps are efficient and robust, manufacturers have aggressive goals on improving efficiency, performance, and range of operations.</div><div> </div><div> In this research, time-accurate computational fluid dynamic (CFD) analyses were performed to study the flow mechanisms in a liquid-ring vacuum pump to understand how it works and how the design can be improved. Based on the understanding gained, a physics based reduced order model was developed for preliminary design of the liquid ring vacuum pumps.</div><div> </div><div> In the CFD analyses, the liquid (water) was modeled as incompressible, the gas (air) as an ideal gas, and turbulence by the shear-stress transport model. The gas-liquid interface was resolved by using the volume-of-fluid method, and rotation of the impeller was enabled by using a sliding mesh. Parameters examined include the suction pressure (75, 300, and 600 Torr) and the impeller's rotational speed (1150, 1450 and 1750 rpm) with the temperature of the gas at the inlet of the suction chamber kept at 300 K and the pressure at the outlet of the exhaust chamber kept at one atmosphere. The CFD solutions generated were verified via a grid sensitivity study and validated by comparing with experimental data. When compared with experiments, results obtained for the flow rate of the gas ingested by the pump had relative errors less than 6\% and results obtained for the power consumed by the pump had relative errors less than 13\%.</div><div> </div><div> Results obtained show the shape of the liquid ring to play a dominant role in creating the expansion ratio or the vacuum needed to draw air into the pump through the suction port and the compression ratio needed to expel the air through the discharge ports. Results were generated to show how centrifugal force from rotation and how acceleration/deceleration from the difference in pressure at the pump's inlet and outlet along with the eccentricity of the impeller relative to the pump's housing affect the shape of the liquid ring. Results were also generated to show how the rotational speed of the impeller and the pressure at the suction port affect the nature of the gas and liquid flow in the pump and the pump’s effectiveness in creating a vacuum. </div><div> </div><div> With the knowledge gained from the CFD study, a physics-based reduced-order model was developed to predict air ingested and power consumed by the pump as well as the liquid ring shape and pressure of the gas and liquid in the pump as a function of design and operating parameters. This model was developed by recognising and demonstrating that the amount of air ingested and power consumed by the pump is strongly dependent on the shape and location of the liquid ring surface. The flow rates of the gas ingested by the pump and the power consumed by the pump predicted by the model were compared with experimental data and relative errors were less than 12\% and 17\% respectively.</div>

This Master Thesis presents TMVOC simulations of a NAPL-spill (non-aqueous phase liquid) and following pumping remediation. TMVOC is a simulation program for three-phase non-isothermal multicomponent flow in saturated-unsaturated heterogeneous media. The models presented are based on an actual remediation project. The aim of the thesis was to study if the historical development of the NAPL-spill could be simulated and how long time the pumping remediation would take. A 3D-model and a radially symmetric cylindrical model were created. A large effort of the work done was in taking the complex TMVOC model in use and modifying it for the problem at hand. Therefore, the numerical results of the simulations should be considered as preliminary and as forming basis for future studies. The results from the spill simulation and historical pumping simulation indicated that the spill volume could be less than the estimated 1400 m3, perhaps around 700 m3, assuming a leakage time of 30 years. The historical pumping simulation of a 700 m3 diesel spill showed good agreement with measured values for some wells, but overestimated the recovery in other wells. The overestimation could be due to the fact that the 3D-model did not take seasonal changes in the groundwater level into consideration. Also, the model did not account for any heterogeneity or compartmentalization in soil material properties that could explain the differences between the wells.  Assuming the same spill of 700 m3, future pumping was simulated. The results from these simulations indicated the remediation time to be long due to fast decreasing mobility of the NAPL phase. The NAPL flow rate to the wells was halved in a couple of years. Much of the NAPL was distributed over a large area at near residual saturation with the highest NAPL saturation found at the opposite side of the pumping wells in the model.   Future simulation studies should address the effect of discretization as well as the effect of uncertainties in material properties e.g. conductivity, residual NAPL saturation and soil heterogeneity.

Les extensions bifluides des méthodes Lattice Boltzmann à frontière libre utilisent généralement des pseudopotentiels microscopiques pour modéliser l'interface. Nous avons choisi d'orienter nos recherches vers une méthode Lattice Boltzmann à capture d'interface où la fraction massique d'un des deux fluides, inconnue, est transportée. De nombreux travaux ont montré les difficultés des méthodes Lattice Boltzmann à traiter des systèmes bifluides, et ce d'autant plus que le ratio de densité est important. Nous expliquerons l'origine de ces problèmes en mettant en évidence le manque de diffusion numérique pour capturer précisément les discontinuités de contact. Pour régler cet obstacle, nous proposerons une formulation Arbitrary Lagrangian Eulerian (ALE) des méthodes Lattice Boltzmann. Cela permet de séparer le traitement des ondes matérielles de celui des ondes de pression. Une fois l'étape ALE terminée, une phase de projection ramène les variables sur la grille eulérienne de calcul initiale. Nous expliquons comment obtenir une procédure de projection ayant une précision d'ordre 2 et une interface fine et dépourvue d'oscillations. Il sera montré que la fraction massique satisfait un principe du maximum discret et qu'elle reste donc entre 0 et 1. Les simulations numériques sont en accord avec la théorie. Même si notre méthode n'est pour le moment utilisée que pour simuler des écoulements de fluides non visqueux (Equations d'Euler), nous sommes convaincus qu'elle pourra être étendue à des simulations d'écoulements bifluides visqueux. / Two-fluid extensions of Lattice Boltzmann methods with free boundaries usually consider ``microscopic'' pseudopotential interface models. In this paper, we rather propose an interface-capturing Lattice Boltzmann approach where the mass fraction variable is considered as an unknown and is advected. Several works have reported the difficulties of LBM methods to deal with such two-fluid systems especially for high-density ratio configurations. This is due to the mixing nature of LBM, as with Flux vector splitting approaches for Finite Volume methods. We here give another explanation of the lack of numerical diffusion of Lattice Boltzmann approaches to accurately capture contact discontinuities. To fix the problem, we propose an arbitrary Lagrangian-Eulerian (ALE) formulation of Lattice-Boltzmann methods. In the Lagrangian limit, it allows for a proper separated treatment of pressure waves and advection phenomenon. After the ALE solution, a remapping (advection) procedure is necessary to project the variables onto the Eulerian Lattice-Boltzmann grid.We explain how to derive this remapping procedure in order to get second-order accuracy and achieve sharp stable oscillation-free interfaces. It has been shown that mass fractions variables satisfy a local discrete maximum principle and thus stay in the range $[0,1]$. The theory is supported by numerical computations of rising bubbles (without taking into account surface tension at this current state of development).Even if our methods are currently used for inviscid flows (Euler equations) by projecting the discrete distributions onto equilibrium ones at each time step, we believe that it is possible to extend the framework formulation for multifluid viscous problems. This will be at the aim of a next work.

Dam spillways and downstream areas are used to guide large flows of water during for example heavy rainfall. The large flows give way to turbulent pattern sand velocities that may damage the river banks or the dam structure. Investigation of these water patterns at certain flows are therefore done to examine at risk areas. In this study CFD simulations were performed for different flows with different boundary conditions for varying surface roughness level. Results were then compared to a previous model study from 2009. The ANSYS ecosystem was used in production of the 3D model, construction of mesh and running of simulations.The flow for the maximum discharge capacity of the sluices was simulated as well as the design flow which is the highest flow the dam is supposed to be able to withstand. In this report the flow has been modeled using RANS with the SST kω-model in a VOF transient setup. Results showed that for both the design flow and the maximum discharge capacity flow the energy conversion is functioning poorly and that a considerable backward circulation exists on the right riverside. This behavior could possibly injure the right dam structure by moving debris upwards against the stream.

No description available.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23503号 / 工博第4915号 / 新制||工||1768(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 黒瀬 良一, 教授 花崎 秀史, 教授 岩井 裕 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

Two-Phase bubbly flows are encountered in a wide range of industrial applications, particularly where phase changes occur as seen in high performance heat exchangers and boiling reactors for power generation. These flows have been extensively studied in channels with circular geometries using air-water flows, though little data exists for flows through narrow rectangular channels. Measurements in thin geometries are particularly challenging since large bubbles bridge the gap, and it is difficult to compare point measurements with photographic techniques. The objective of this study is to explore the abilities of hot-film anemometry and high speed photography for taking measurements in a narrow vertical rectangular channel for a range of volume fractions, with particular attention on the narrow dimension. Hot-film anemometry (HFA) is a measurement technique originally developed for the measurement of fluid velocities, but has since been found to have applications for broader measurements in multiphase flow. With the sensor operating on the principle of heat loss, the method takes advantage of the differing abilities of the phases to transport heat, with each phase leaving its own signature in the signal response. The linchpin of this method lies in the ability to accurately distinguish between the two phases within the signal, and to execute this operation, various algorithms and techniques have been developed and used with some success for a wide range of flow conditions. This thesis is a study of the various methods of analysis such as amplitude threshold for triggering, and small slope threshold for finely tuning the edges of the bubble interactions, and demonstrates the capabilities of the hot-film sensor in a narrow rectangular vertical duct with a high aspect ratio. A vertical acrylic test section was fabricated for the purposes of this study, inset with a rectangular channel 38.1mm in width and 3.125mm in depth. Experiments were conducted for volume fractions ranging from 2% to 35%, which remained within the limits of the bubbly flow regime, but ranged from small uniform bubbles to larger bubbles coalescing into a transition regime. The hot-film signal was analyzed for void fraction, bubble speed, and bubble size. An in-depth study of the various methods of phase discrimination was performed and the effect of threshold selection was examined. High-speed video footage was taken in conjunction with the anemometer data for a detailed comparison between methods. The bubble speed was found to be in close agreement between the HFA and high-speed video, staying within 10% for volume fractions above 10%, but still remaining under a 30% difference for even as low as the 2% volume fraction, where measurements have been found to be historically difficult. The trends with volume fraction between the HFA and high-speed results were very similar. A correlation for narrow rectangular channels employing a simple drift flux model was found to compare with the void fraction data where appropriate. Good agreement was found between the methods using a hybrid phase discrimination technique for the HFA data for the void fraction and bubble speed results, with the high-speed video results showing a slight over-estimation in regards to the bubble size.

Determination of particle slip is a major concern for particle based measurements in un- heated supersonic facilities, as it is a limiting factor for the instruments' frequency response. For the purpose of determining the particle deceleration through a stationary shock wave in a super sonic windtunnel, a novel 1-D Laser Doppler probe with an unique spatial range (~1.5 mm) is presented. The study first gives a short review of the physics of particle motion with respect to different drag models and flow regime encountered in super sonic flows. In the second part, the focus lies on the development of a new Laser Doppler probe using non Gaussian beams to obtain a prolonged measurement volume. This volume covers a major part of the particle lag after a shock wave. An experimental investigation on particle acceleration and drag, using different types and sizes of seeding material, including standardized microspheres is carried out in the Mâ = 2.0 super sonic facility. Three different types of particles with four different sizes are experimentally investigated. The experimental data provides mean velocity as a function of distance from the shock and reveals significant agglomeration and evaporation problems with Titanium Oxide and Polystyrene Latex spheres. Particle acceleration measurements are presented, proving the unique concept of the new Laser Doppler probe. Mean and instantaneous acceleration data is extracted from high SNR signals. The acceleration data obtained is consistent in magnitude and trend with the physical phenomena expected and shows the feasibility of the new instrument. / Master of Science