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Due to its advantages, the air lift pump has many applications in real life. Therefore, the present study is dealing with the effect of some parameters on the air lift pump performance. The present study is a continuation of a program started years ago by the fluid mechanics group in Faculty of Engineering, Alexandria University. Beginning by validating the obtained results of the experiment set-up by comparing these experimental results with international accepted sets of data. After that the present experiments shed some lights on the inlet injection region of the air lift pump due to the significant effect of its initial conditions on the pump efficiency. Thus the study directed towards investigating the effect of some parameters including the inlet restrictor resistance, the injection direction and the injector riser diameter. The upward injection technique shows higher peak efficiency of 34.7% compared to 29.7% and 28.9% for downward and side injection respectively while the larger injector inner diameter shows maximum water capacity of 928 kg/h. compared to 823 kg/h. water mass flow rate for the smaller inner diameter injector. In all the above experimental tests, flow visualization is used extensively giving a good agreement with well recognized flow pattern map.

Two-phase pressure drop in the debris has been studied by many researchers concerning the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional models for gas-liquid two-phase flow pressure drop have not been established to evaluate interfacial drag accurately. In this study, high-speed imaging of a two-dimensional network model was performed to clarify the effect of flow patterns on interfacial drag and pressure drop. Usually, it would not be easy to visualize such two-phase flow behavior in a randomly packed bed due to the reflection/refraction of light and/or overlapping bubbles, even if the test section is made of transparent materials. Therefore, in this study, a test section, which simulates a two-dimensional network of porous structures, was fabricated to avoid overlapping bubbles. The two-phase flow pattern in the porous structure has been identified by high-speed imaging of the two-dimensional network model. The flow regime map based on the flow pattern visualization results is applied to the pressure drop evaluation and it could reduce the overestimation of experimental values. The experimental results suggested that the interfacial drag term should be modified in the gas-liquid two-phase flow pressure drop model.

Increasing environmental concerns with climate change have led many people around the world to demand urgent action, forcing national governments to seek alternatives to carbon-based fuels. In the light of all this, it is of critical importance for our civilization that carbon-based energy sources are rapidly replaced by renewable and sustainable sources without carbon emissions. For this reason, the use of these clean energy sources and the efficiency of the processes in their production is a very important issue. In this study, 3-dimensional, two-phase (hydrogen and water) computational fluid dynamics (CFD) analysis was performed in a polymer electrolysis membrane cell (PEM). Analysis took place for 30 seconds. The water flow rate was kept constant at 260 ml/min. As a result of the analysis, pressure, gas volume fraction and velocity data in the manifolds and in the electrolysis channels where the electrolysis process takes place were interpreted. While the pressure change in the cell was quite high in the range of 0-1.8 seconds from the beginning of the flow, it was observed that a balance was formed in the pressure distribution after 1.8 seconds. It is understood that the number of channels in the model is a factor for the pressure inside the manifold and the cell. However, it was observed that the unit gas production amount in the cell also changed along the channels., İklim değişikliğiyle beraber yükselen çevresel kaygılar, dünyada birçok insanın acil eylem talep etmesine yol açarak, ulusal hükümetleri karbon kaynaklı yakıtların alternatiflerini aramaya mecbur bırakmıştır. Tüm bunların ışığında karbon kaynaklı enerji kaynaklarının yerini süratle karbon emisyonu olmayan yenilenebilir ve sürdürülebilir kaynakların alması medeniyetimiz için kritik bir öneme sahiptir. Bu sebeple bu temiz enerji kaynaklarının kullanımı ve üretimindeki proseslerin verimliliği oldukça önemli bir konudur. Bu çalışmada bir polimer elektroliz membran hücresinde (PEM), 3 boyutlu, iki fazlı (hidrojen ve su) hesaplamalı akışkanlar dinamiği (CFD) analizi yapılmıştır. Analiz 30 sn boyunca gerçekleşmiştir. Su akış hızı 260 ml/dk olarak sabit tutuldu. Analiz sonucunda manifoltlarda ve elektroliz işleminin gerçekleştiği elektroliz kanallarında basınç, gaz hacim fraksiyonu ve hız verileri yorumlandı. Akış başlangıcından itibaren 0-1.8 sn aralığında hücre içindeki basınç değişimi oldukça fazlayken, 1,8.saniyeden sonra basınç dağılımında bir dengenin oluştuğu gözlemlenmiştir. Modeldeki kanal sayısının manifold ve hücre içindeki basınç için bir faktör olduğu anlaşılmıştır. Bununla birlikte hücredeki birim gaz üretim miktarının da kanallar boyunca değiştiği gözlemlenmiştir.

Despite the importance of droplet monodispersity, a universal methodology for high monodispersity droplet generation does not exist yet. We have recently demonstrated that unlike the conventional method of droplet generation, applying an identical pressure from a single source makes the microfluidic droplet system immune to the external fluctuations that originate from the imperfection of the flow source. In this work, we show that our method is universal and applicable to other common microfluidic devices and flow sources. We applied this method to flow-focusing and coflow devices that are commonly used for high-frequency microdroplet generation. In addition to the pressure pump, we used a syringe pump to show that our method is applicable to flow rate controllable systems as well. We compared the monodispersity of droplets formed by the conventional methods and the novel method explained in this work. © 2022 The Authors

V magisteriju smo opravili toplotno analizo prototipa diverterskega elementa za stelarator W7-X, ki je sestavljen iz nosilne strukture, toplotnega ščita, medsloja in hladilnega kanala z vodo. Analizirali smo temperaturno porazdelitev elementa pri predvidenih pogojih obratovanja. Analizo smo numerično izvedli na podlagi metode kontrolnih volumnov s programskim paketom za računalniško dinamiko tekočin ANSYS CFX. Za verifikacijo modela diverterske enote smo opravili analizo občutljivosti računske mreže. Za validacijo izbranega modela vrenja smo primerjali rezultate simulacije z dostopnimi eksperimentalnimi podatki. Simulacije so obsegale različne materiale ščita, toplotne obremenitve ter tudi z vključitvijo spiralnega vložka v hladilni kanal. V modelu smo najprej privzeli model enofaznega turbulentnega toka vode v hladilnem kanalu na podlagi modela SST, kjer smo reševali sklopljen prenos toplote za trdnino in tekočino. Na podlagi parametrične študije smo ugotovili, da temperature materialov komponent v nobenem od analiziranih primerov ne dosežejo kritičnih vrednosti. Na posameznih mestih lahko temperatura stene hladilnega kanala presega temperaturo vrelišča vode. Zato smo opravili tudi dvofazno simulacijo toka z vključenim modelom vrenja. Rezultati kažejo, da je količina pare, ki nastane zaradi vrenja pri obratovalnih pogojih zanemarljiva, in zato ne predstavlja nevarnosti za prehod v filmsko vrenje. In this thesis we conducted thermal analysis of the prototype divertor element for W7-X stellarator, composed of the supporting structure, heat shield, interlayer and a cooling channel with water. We have analysed the temperature distribution at anticipated operating conditions. Based on the finite volume method, we performed the numerical analysis with the ANSYS CFX software. To verify the model of the diverter unit, we performed a sensitivity analysis of the computational mesh. We compared the simulation results with available experimental data to validate the selected boiling model. The simulations included different shielding materials, thermal loads and inclusion of a spiral insert in the cooling channel. In the model, we first adopted the model of a single-phase turbulent flow of water in the cooling channel based on the SST model, where we solved the coupled heat transfer for the solid and the liquid. Based on the parametric study, we found that the temperatures of the component materials do not reach critical values. At individual places, the temperature of the cooling channel wall can exceed the boiling temperature of water. Therefore, we also performed a two-phase flow simulation with the included boiling model. Results show that the amount of vapour generated by boiling is negligible and therefore does not pose a danger of transitioning into a film boiling.

Electrowinning is the process of depositing copper of the electrolyte solution inside the cell to the cathode. In the present study, the hydrodynamic simulation of the electrowinning cell of Miduk Copper Complex is studied using computational fluid dynamics. The software used is Ansys CFX. The Navier-Stokes and continuity equations are considered in the form of two phases of fluid and gas, turbulent, incompressible and steady state, and the equation for copper concentration in the electrolyte is solved with consideration of its specific boundary condition. The flow turbulence is modeled using K-ω relationships. Due to large variations in the properties near cathode and anode, and also the large size of the electrowinning cell, to create a good grid, and increase the speed and accuracy of the results, global and local simulations are used together. First, in global simulation, the entire geometry of the cell is modeled by creating an appropriate grid, then, in the local simulation, the volume between two cathodes of the cell only is considered and modeled with a much smaller mesh. Data on boundary conditions of the common border plates in the local simulation are obtained from global simulation data, which increases the accuracy of modeling. The results of this simulation are the velocity vectors, the concentrations of acid and copper, turbulence Intensity, the amount of pressure, and the volume ratio of the oxygen phase in the entire electrowinning cell domain. Finally, for model validation, the model is compared with experiments conducted on actual cells in the industry. Results show high accuracy with less than 2.5% deviation of this modeling technique. Then, the mass transfer coefficient values for the different electrode intervals are obtained by this modeling and the results are validated using the results of the experimental relations, indicating a deviation of only 0.5%. In the next step, the electrolyte mixture containing different mass fractions of oxygen is sprayed into the electrowinning cell from the inlet of the simulated cell. The results demonstrate that spraying 16 liters per second of oxygen at the inlet can increase the overall mass transfer coefficient of the electrode plates up to 7%. The effect of changing inlet temperature and flow rate of the electrolyte on the mass transfer coefficient is also investigated by the obtained model.

The trapped air in the water conveyance systems may cause the obstruction of flow, corrosion and adverse effect on the performance of valves and pumps. This study is part of the Abbas Abad Dam Drinking Water Transmission Line using Ansys Fluent Software, The behavior of air entrapped during the filling and discharging process and the effect of its existence on pressure changes were studied. Entrapped air was simulated at 0.5, 2, 3 m lengths and inlet pressures of 1.2456, 1.7456 and 2.2456 atmospheres for a 35-meter-long metal pipe with a discharge valve embedded in its outlet end. The effects of pressure-time changes were investigated in two ways: a) pressure changes in the pipe and drain valve and b) pressure changes inside the entrapped air. The results showed that the pressure changes in both cases were due to the large fluctuations in confined air and that the fluctuations continued until the drain valve was fully opened and the longer the confined air length was, the greater the amplitude and length of the created fluctuations. Modeling with similar boundary conditions without the presence of air indicates no pressure fluctuations. The results of the verification confirm the research results. Besides the Palau et al, 2019 results, calculation of relative error, RMSE and NRMSE were used in order to validate the numerical model results.

The purpose of this paper is to understand the capability and consistency of large eddy simulation (LES) in Eulerian–Lagrangian studies aimed at predicting inertial particle dispersion in turbulent wall-bounded flows, in the absence of ad hoc closure models in the Lagrangian equations of particle motion. The degree of improvement granted by LES models is object of debate, in terms of both accurate prediction of particle accumulation and local particle segregation; therefore, we assessed the accuracy in the prediction of the particle velocity statistics by comparison against direct numerical simulation (DNS) of a finer computational mesh, under both one-way and two-way coupling regimes. We performed DNS and LES at friction Reynolds number Re τ= 180 in smooth and rough channels, tracking particles with different inertia, with the aim to conduct a parametric study that examines the accuracy of particle statistics obtained from LES computations. The issue has been widely analysed in turbulent flow bounded by smooth walls, whereas the effect of rough boundaries on momentum coupled two-phase flows has been much less investigated until now. The action of the roughness of the wall is studied in terms of both turbulence modification and particle interaction with the wall surface due to particle rebounding off the solid boundary, without the introduction of a virtual rebound model. Results show that resolved LES adequately predicts particle-induced changes in both fluid and particle statistics in rough channels, at least for the range of parameters considered here. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.

Erosion wear of the centrifugal pump impeller are the key issues since its operating in sediment-laden flow. Experiment and numerical method are adopted in this study to investigate the erosion wear of the impeller in a double-suction pump in the Jingtai Yellow River Irrigation Project (JYRIP). Observation during operation combined with morphology study is carried out to verify erosion mechanisms at the different sections of the impeller blade. For numerical study, the Eulerian-Lagrangian approach combined with the Mclaury model is employed to predict the trajectories of the particles under different particle parameters. Also the effects of particle size and concentration on impeller erosion wear is studied. Numerical results are consistent with experimental data. The surface wear of the blade changes obviously from circular shape to strip shape in the direction from the Leading Edge (LE) to the Trailing Edge (TE), and the wear damage area increases correspondingly. Trajectories of larger particles are more uniform and tend to cause more severe erosion wear damage. The wear damage tends to be slow after the particle size increases to a certain extent under the same sediment concentration. Besides, erosion rate increases with an increase in sediment concentration, and the erosion rate of the suction side is greater than the pressure side at the same position of the blade surface. These results can offer a good reference for the design of wear resistance impeller of the double suction pump.

Two-phase flow through porous media leads to the formation of drops and fingers, which eventually break and merge or may be trapped behind obstacles. This complex dynamical behavior highly influences macroscopic properties such as the effective permeability and it also creates characteristic fluctuations in the velocity fields of the two phases, as well as in their relative permeability curves. In order to better understand how the microscopic behavior of the flow affects macroscopic properties of two phases, we simulate the velocity fields of two immiscible fluids flowing through a two-dimensional porous medium. By analyzing the fluctuations in the velocity fields of the two phases, we find that the system is ergodic for large volume fractions of the less viscous phase and high capillary numbers Ca. We also see that the distribution of drop sizes m follows a power-law scaling, (Formula presented.). The exponent ξ depends on the capillary number. Below a characteristic capillary number, namely Ca* ≈ 0.046, the drops are large and cohesive with a constant scaling exponent ξ ≈ 1.23 ± 0.03. Above the characteristic capillary number Ca*, the flow is dominated by many small droplets and few finger-like spanning clusters. In this regime the exponent ξ increases approaching 2.05 ± 0.03 in the limit of infinite capillary number. Our analysis also shows that the temporal mean velocity of the entire mixture can be described by a generalization of Darcy’s law of the form (Formula presented.) where the exponent β is sensitive to the surface tension between the two phases. In the limit of infinite capillary numbers the mobility term increases exponentially with the saturation of the less viscous phase. This result agrees with previous observations for effective permeabilities found in dissolved-gas-driven reservoirs., Frontiers in Physics, 10, ISSN:2296-424X

Accurate prediction of wave loads from extreme waves on individual beams in offshore jacket structures are important to ensure the structural integrity. As the load distribution along a beam is strongly tied to the wave kinematics it is crucial to have an accurate prediction of the surface elevation and the velocity field. The open-source CFD code OpenFOAM contains two solution algorithms (interFoam and interIsoFoam), which are used for ocean wave simulations and wave load predictions. The algorithms are often applied using a too coarse spatial discretisation, which violates the assumption of a continuous solution at the free surface. The consequence is inaccurate and unphysical predictions even for propagation of a steady wave. Our recently developed Direct Surface Description (DSD) solution algorithm in OpenFOAM is used to simulate a solitary wave with different cell aspect ratios. The solitary wave case shows that the DSD method provides accurate velocity fields and surface elevations both for square and horizontally elongated cells.

Disintegration of liquid masses in a free-surface flow is still an open question in the field of small-scale spray applications such as dispensing of detergents or sanitizing products. In this context, the pressure-swirl atomizer is widely investigated. It allows to improve several spray characteristics through the formation and breakup of a conical liquid sheet that results in the well-known hollow-cone atomization. From this perspective, the characterization of a small-scale pressure-swirl spray under laminar flow conditions is the focus of this work. The configuration of the device and the physical properties of the discharged liquid are the key parameters that modify the attributes of such multiscale flow. In this regard, the entire picture of the fragmentation process is structured into multiple stages: internal nozzle flow, outer displacement of the liquid–gas interface, droplet spread into the atmosphere, and droplet-wall interactions on a collection surface. Through the computational fluid dynamics, we analyze the influence of the main fluid/packaging parameters on the hollow-cone spray properties, and on the whole atomization process. Reynolds and Ohnesorge numbers are coupled with the Sauter mean diameter to distinguish different breakup mechanisms and spray performances. The solution of the entire spray system is performed by implementing the volume-of-fluid-to-discrete-phase-model, which allows to capture the liquid–gas interface displacement and track the droplets produced downstream the primary atomization, simultaneously. With this Eulerian–Lagrangian hybrid model, we link key features of the hollow-cone spray process to spray pattern and droplet size distribution for both Newtonian and non-Newtonian fluid properties.

In this study, Galerkin weighted residual Finite Element Method is used to find the thermophoresis and Brownian diffusion motion of two phase nanofluid flow around a vertical cone in porous media. Gravity, Drag, Thermophoresis and Brownian forces are confided on the nanoparticles to find their motion during the time. The problem is solved in both transient and steady conditions. The effect of Nc and Nv parameters on the temperature and velocity profiles are investigated. Also, the effect of boundary conditions on the temperature and nanoparticles concentrations are investigated through the graphical contours. As a main result, variable thermal conductivity parameter (Nc) increament from zero to unity increased the velocity and temperature profile values, while had not significant effect on the nanoparticles concentration. Also, results revealed that increasing the Nv (from 2 to 200) and Nc (from 0 to 1), increased the (− θ ′ ( 0 ) ) and (− f ′ ( 0 ) ) to 1.36% and 0.15%, respectively.

Two phase flow and horizontal well completion pose additional challenges for rate-transient analysis (RTA) techniques in under-saturated coal seam gas (CSG) reservoirs. To better obtain reservoir parameters, a practical workflow for the two phase RTA technique is presented to extract reservoir information by the analysis of production data of a horizontal well in an under-saturated CSG reservoir. This workflow includes a flowing material balance (FMB) technique and an improved form of two phase (water + gas) RTA. At production stage of a horizontal well in under-saturated CSG reservoirs, a FMB technique was developed to extract original water in-place (OWIP) and horizontal permeability. This FMB technique involves the application of an appropriate productivity equation representing the relative position of the horizontal well in the drainage area. Then, two phase (water + gas) RTA of a horizontal well was also investigated by introducing the concept of the area of influence (AI), which enables the calculation of the water saturation during the transient formation linear flow. Finally, simulation and field examples are presented to validate and demonstrate the application of the proposed techniques. Simulation results indicate that the proposed FMB technique accurately predicts OWIP and coal permeability when an appropriate productivity equation is selected. The field application of the proposed methods is demonstrated by analysis of production data of a horizontal CSG well in the Qinshui Basin, China.

In this paper, flow patterns in a circular water tank with three different aeration rates are in estimated by gas and liquid phase flow simulations. As the result, vortex center positions measured from visualization experiments had a good agreement with simulation ones. And when the aeration rates increase, the strength of large vortex increased.

The penetration of fuel spray as a result of the mixture of fuel droplet and entrained air usually generate nonlinear models whose solutions are normally difficult to realize analytically. This present study presents general approximate analytical solution to such problem by employing Differential transform Method (DTM). At the level of two-phase flow, the spray droplets and the entrained air have the same flow velocity. In order to fully understand the process, the parameters present in the governing equations are carefully studied. The obtained solution employing DTM is verified with Numerical Runge-Kutta (RKF45) and also compared with similar past works. Furthermore, the acquired results for different ambient densities and injection velocities are depicted and discussed. The results illustrate that continuous increase in the initial velocity and orifice diameter cause a corresponding increase in spray penetration while an antonymous effect is noticed for an increased semi cone angle and density. This work will find vital applications in the optimization of systems whose operation are influence by the aforementioned spray penetration processes.

EgeUn###, In this study, implementation of a thermosyphon heat exchanger into a Stirling refrigeration system is demonstrated by means of both theoretical and experimental analyses. R-134a was employed as the working fluid which formed a liquid column at the condenser exit, enabling a two-phase flow through the evaporator. Experiments were conducted in a controlled chamber. Cooling capacity, coefficient of performance, and two-phase pressure drop of the cooler were compared at two different voltages. The flow regime for the refrigerant in the evaporator was found to be stratified based on the calculated wavy flow and Lockhart-Martinelli parameters.

Understanding multiphase flow and gas transport occurring in electrodes is crucial for improving the performance of proton exchange membrane fuel cells. In the present study, a pore-scale model using the lattice Boltzmann method (LBM) was proposed to study the coupled processes of air–water two-phase flow and oxygen reactive transport processes in porous structures of the gas diffusion layer (GDL) and in fractures of the microscopic porous layer (MPL). Three-dimensional pore-scale numerical results show that the liquid water generation rate is gradually reduced as the oxygen consumption reaction proceeds, and the liquid water saturation in the GDL increases, thus the constant velocity inlet or pressure inlet condition cannot be maintained while the results showed that at t = 1,200,000 iterations after 2900 h running time, the local saturation at the GDL/MPL was about 0.7, and the maximum value was about 0.83, while the total saturation was 0.35. The current density reduced from 2.39 to 0.46 A cm−2. Effects of fracture number were also investigated, and the results showed that for the fracture numbers of 8, 12, 16, and 24, the breakthrough point number was 4, 3, 3, and 2, respectively. As the fracture number increased, the number of the water breakthrough points at the GDL/GC interface decreased, the liquid water saturation inside the GDL increased, the GDL/MPL interface was more seriously covered, and the current density decreased. The pore-scale model for the coupled multiphase reactive transport processes is helpful for understanding the mechanisms inside the porous electrodes of PEMFC.

When converting a baffled stirred reactor to work with a different fluid, usually the original impeller must be replaced with a customized one. If the original impeller was designed for mixing liquids, its performance for liquid–solid suspensions may not be satisfactory. A case study is presented, where a two-blade original impeller is replaced with a new three-blade design. The new impeller shows clear improvements in mixing a liquid–solid suspension, while keeping the shaft power practically at the same level. As a result, a practically homogenous liquid–solid mixture is obtained, thus ensuring the required quality of the final product. The present numerical investigations employ the Eulerian multiphase model with renormalization (RNG) k–ε turbulence model to simulate the three-dimensional unsteady free-surface liquid–solid flow in a stirred tank. A sliding mesh approach was used to account for the impeller rotation within the expert code, FLUENT 16. The comparative quantitative analysis of the solid phase distribution and the relevant velocity profiles show that the new design of three-blade-impeller is significantly increasing the sedimentation time of the solid phase beyond the chemical reaction specific time. The necessary power to drive the new impeller has a slightly higher value than for the original impeller but it can be sustained by the existing driving system.

In this paper, a full 3D transient Computational Fluid Dynamics (CFD) model of a twin screw compressor with oil injection is described in detail. Volume of Fluid (VOF) two phase flow model is used for gas and liquid phases. The rotor meshes are generated by SCORGTM grid generator and read into the CFD solver at each time step. The simulation runs efficiently and results are obtained in about 12 hours on 24 CPU cores. The CFD prediction of air mass flow rate and indicated power has a good agreement with the experimental data measured at City University of London. The compression pocket is tracked using a customized postprocessing technique and the pressurevolume diagram within it is also obtained and analyzed. Simulations demonstrate that the approaches used in this paper are robust and fast, and can be readily applied to industrial compressor systems for rapid design iterations and improvements.

Nanofluid is a new class of fluid that aims to enhance heat transfer. Nanoparticles sedimentation may play a role in the heat extractions from a hot surface. Brownian and thermophoretic effects may help in understanding the sedimentation effects. In the present paper, we attempted to investigate these phenomena (Brownian motion and thermophoretic effects) in three-rectangular channel configurations heated from below. The working fluids we considered are three different mixtures with 1%vol Al2O3 nanoparticles in various base fluids such as water, ethylene glycol, and a mix of 50% water and 50% ethylene glycol. Different flow rates were implemented in the model using the finite element technique. Results revealed that 1%vol Al2O3/water is the best mixture for heat removal based on thermal efficiency criteria. The presence of solid-blocks in the channel further enhanced the performance of the 1%vol Al2O3/water nanofluid; when the height/base of the blocks increases. As the nanoparticles diameter increases, the average Nusselt number and the thermal efficiency of nanofluid also increases. It appears that between 31 to100 nm particle diameter, the increase in heat extraction is minimal. For a Reynolds number below 600, as the nanoparticles diameter increase above 31 nm, the sedimentation increases accordingly. However, regardless of the nanoparticle's diameter, for a Reynolds number in the range of 840, uniform nanoparticles distribution is observed.

The safety assessment of a radioactive waste disposal facility installed in very low permeable clay rocks is one of the major issues this thesis aims to contribute. We focused on studying, through the SPH method, the mechanical response at the pore-scale of the Callovo-Oxfordian clay (COx) in a coupled phenomenon related to the gas migration.An in-depth study of solid material response through SPH solver was proposed. Small and large deformations were considered, where for the latter, a Total Lagrangian version was implemented through the Saint Venant-Kirchhoff constitutive model. First, an investigation for finite values of the SPH kernel support length was performed, which allowed characterising higher-order effects (also called non-local effects). The non-local effects appear to be directly related to the support-length parameter, which is purely numerical (and inherent to the SPH). We also proposed a non-local SPH-based approach to compute damage and fracture. The width of the localised damage zone is independent of the discretisation, and it is related to the kernel support-length. In quasi-static simulations, it was observed that the fracture propagation, which follows the damage localisation, was accompanied by an increase of kinetic energy and the discontinuity of the displacement fields.A set of SPH drainage simulations within a realistic porous material (COx clay) was proposed. The drainage led to the pore-space dilation during gas percolation. We showed that different confining pressure can affect the onset of fracturing with new pore space creation and also that initially isolated pores can be connected generating new percolating pathways.; L'évaluation de la sûreté d'une installation de stockage de déchets radioactifs installée dans des roches argileuses à très faible perméabilité est l'un des enjeux majeurs de cette thèse. A l’aide de la méthode Smoothed Particle Hydrodynamics (SPH), nous avons étudié la réponse mécanique de l'argilite du Callovo-Oxfordien (COx) dans un phénomène hydromécanique couplé lié à la migration des gaz, notamment la caractérisation du phénomène de chemin préférentiel à l'échelle des pores. Nous avons proposé une étude approfondie de la réponse des matériaux solides via le solveur SPH et sa fonction de lissage. Nous avons démontré avec précision la prise en compte des effets non-locaux dans l’élasticité et dans l’endommagement. Ces effets sont introduits de façon purement numérique et sont indépendants de la discrétisation. Dans ce contexte, le modèle proposé a conservé une équation locale du modèle d'endommagement à partir d’une formulation thermodynamique, tandis que la régularisation non locale a été effectuée numériquement. Nous observons que la largeur des zones endommagées est liée à la longueur de support de la fonction de lissage, ce qui confirme que ce paramètre numérique joue un rôle physique et peut être ajusté aux propriétés matérielles. Les simulations de drainage dans l’espace poreux d’un échantillon de COx conduisent à la dilatation des pores lors de la percolation du gaz. Nous avons démontré que la pression de confinement peut affecter le phénomène de fracturation de la matrice argileuse avec la création d'un nouvel espace poreux ainsi qu'il est possible de connecter des pores initialement isolés et de générer de nouveaux domaines d’écoulement percolant.

A mathematical model of the bubble pump is established by employing the governing equations; the continuity, momentum and energy equations. The model was used to evaluate the performance of the pump under different geometrical and operational conditions. Different parameters including the pump tube diameter, the pumping head, and solar heating input were considered in the analysis. The flow rates of both phases (liquid and vapor) were predicted for each set of parameters. Methanol was used as the working fluid. The performance is presented for a number of different scenarios. The flow was found to be increased with both larger diameters and low static heads, while it has a roughly sine curve with the heat input. A set of results show that for a tube diameter of 10 mm and pumping head of 450 mm, increasing the heat input from 300 W to 500 W increases the mass flow rate of vapor from 0.04 kg/sec to 0.08 kg/sec, while the liquid flow increases from 0.075 kg/sec to 0.22 kg/sec, respectively. Generally, the results of this study were found to be in fair agreement with published results.

Crude oil extraction and production lead to the formation of an emulsion of water and oil, which must be separated before being conveyed to the process installation or re-injected in the reservoir. Reducing the cost of the separation by optimizing the system requires a good understanding of the physics of emulsions. Emulsions are a multiscale/multiphysics problem involving a wide range of length scales and time scales. In particular, coalescence is a key process to be understood. Due to the difficulty of physical experimentations, numerical simulations of emulsions are appealing. Where using a single VOF function always allows coalescence at the mesh size and using different VOF functions for different drops always avoid coalescence (it is computationally expensive to use as many VOF functions as there are drops). Based on the idea that drops far enough away from one another can use the same VOF function, an efficient algorithm is developed to avoid coalescence for a large number of drops using only a few VOF functions. Furthermore, these non-coalescing drops can also be tracked over time and allowed to coalesce after the desired amount of contact time. This opens the door for efficient subgrid-scale modeling of the coalescence process. The analysis of large coalescing and non-coalescing emulsions with Bo = O(1) and Ar = O(1) have shown instabilities with a wavelength independent from the domain size characterized by the drop diameter. In coalescing emulsions filaments formation controlled by the domain size appeared. The delay in total settling time of an emulsion is also demonstrated by varying the coalescence time using the control coalescence algorithm., L'extraction et la production de pétrole brut conduisent à la formation d'une émulsion d'eau et d'huile, qui doit être séparée avant d'être acheminée vers l'installation de procédé ou réinjectée dans le réservoir. Réduire le coût de la séparation en optimisant le système nécessite une bonne compréhension de la physique des émulsions. Les émulsions sont un problème multi-échelles / multiphysiques impliquant une large gamme d'échelles de longueur et d'échelles de temps. En particulier, la coalescence est un processus clé à comprendre. En raison de la difficulté des expérimentations physiques, les simulations numériques d'émulsions sont attrayantes. Lorsque l'utilisation d'une seule fonction VOF permet toujours la coalescence à la taille du maillage et l'utilisation de différentes fonctions VOF pour différentes gouttes évite toujours la coalescence (il est coûteux en calcul d'utiliser autant de fonctions VOF qu'il y a de gouttes). Sur la base de l'idée que les chutes suffisamment éloignées les unes des autres peuvent utiliser la même fonction VOF, un algorithme efficace est développé pour éviter la coalescence d'un grand nombre de gouttes en utilisant seulement quelques fonctions VOF. En outre, ces gouttes non coalescentes peuvent également être suivies dans le temps et autorisées à fusionner après la durée de contact souhaitée. Cela ouvre la porte à une modélisation efficace à l'échelle du sous-réseau du processus de coalescence. L'analyse de grandes émulsions coalescentes et non coalescentes avec Bo = O (1) et Ar = O (1) a montré des instabilités avec une longueur d'onde indépendante de la taille de domaine caractérisée par le diamètre de goutte. Dans les émulsions coalescentes, une formation de filaments contrôlée par la taille du domaine est apparue. Le retard du temps de stabilisation total d'une émulsion est également démontré en faisant varier le temps de coalescence à l'aide de l'algorithme de coalescence témoin.

The settling of drilling cuttings is important for the drilling and clean-out operations. The current article provides a Computational Fluid Dynamics (CFD) modeling study of particle settling behavior during the drilling operations, with a special focus on the impact of fluid rheology, flow regime, particle size and shape on the settling rate. The Eulerian-Lagrangian method are adopted to track particle trajectories in a shear-thinning fluid under quiescent conditions. The rheological properties of the drilling fluids are described by different rheological models. Settling of spherical and ellipsoidal cuttings, with various aspect ratios, is studied for particles with a diameter ranging between 2 and 6 mm. The settling behavior is predicted for particles with narrow (0.5–2 mm), medium (0.5–6 mm) and broad (0.5–10 mm) particle size distributions (PSD). Applying a non-Newtonian power-law model at low shear rates, where the fluid is in the Newtonian regime, resulted in 11–19% over-prediction of settling velocities as compared to the experimental data. On the other hand, ignoring the particle-induced shear rate by assuming a Newtonian fluid behavior in the transition regime showed 8–10% difference between the estimated and experimental settling rates. Therefore, the CFD computations of settling rates suggest that Cross and Carreau models provide more accurate predictions than a simple power-law model. The selection of the suitable rheological model is a key factor in predicting settling in drilling fluids. This is more important for small particles where the Newtonian behavior is dominant and particle-induced shear rate is low. Ellipsoidal cuttings exhibited significantly greater resistance to settling as compared to spherical particles, mainly due to the increased drag force. Further, the terminal settling velocity of ellipsoidal cuttings consistently increased with the particle aspect ratio. Cuttings with broad PSD showed ~32 times higher settling velocity than particles with narrow PSD. CFD results are validated with experimental measurements. Moreover, results for settling of non-spherical particles are validated with an empirical correlation. Agreement of experimental and theoretical predictions is observed when the fluid and flow regimes are well identified and described This work was made possible by the support of a National Priorities Research Program (NPRP) grant from the Qatar National Research Fund (QNRF), grant reference number NPRP11S-1228?170140. The statements made herein are solely the responsibility of the authors. The authors would like to acknowledge Qatar National Library (QNL) for providing open access to this article. Scopus

It is clear that the entire world have to research, develop, demonstrate and plan for alternative energy systems for shorter term and also longer term. As a clean energy carrier, hydrogen has become increasingly important. It owes its prestige to the increase within the energy costs as a result of the equivocalness in the future availability. Two phase flow and hydrogen gas flow dynamics effect on performance of water electrolysis. Hydrogen bubbles are recognized to influence energy and mass transfer in gas-evolving electrodes. The movement of hydrogen bubbles on the electrodes in alkaline electrolysis is known to affect the reaction efficiency. Within the scope of this research, a physical modeling for the alkaline electrolysis is determined and the studies about the two-phase flow model are carried out for this model. Internal and external forces acting on the resulting bubbles are also determined. In this research, the analytical solution of two-phase flow analysis of hydrogen in the electrolysis is analyzed. © 2021 Hydrogen Energy Publications LLC 2-s2.0-85104485492

The multiscale hybrid mixed finite element method (MHM-H(div)), previously developed for Darcy's problems, is extended for coupled flow/pressure and transport system of two-phase flow equations on heterogeneous media under the effect of gravitational segregation. It is combined with an implicit transport solver in a sequential fully implicit (SFI) manner. The MHM-H(div) method is designed to cope with the complex geometry and inherent multiscale nature of the phenomena.The discretizations are based on a general domain partition formed by polyhedral subregions, where a hierarchy of meshes and approximation spaces are considered. The multiscale approach is applied to the flux/pressure kernel making use of coarse scale normal fluxes between subregions (trace variable). The fine-scale features inside each subregion are determined by resolving completely independent local Neumann problems, the boundary conditions being set by the trace variable, by the mixed finite element method using fine flux and pressure representations. These properties imply that the MHM-H(div) can be interpreted as a classical mixed formulation of the model problem in the whole domain, based on a $H(\divop)$-conforming space with normal components over the macro-partition interfaces constrained by the trace space, and showing divergence compatibility with the pressure space. Consequently, local mass conservation is observed at the micro-scale elements inside the subregions, an essential property forflows in heterogeneous media, and divergence-free constraint strongly enforced for incompressible flows. The efficient use of static condensation leads to a global system to be solved only in terms of primary degrees of freedom associated with the trace variable and of a piecewise constant pressure for each subregion. This procedure allows a substantial reduction of the dominant computational costs associated with the flux/pressure kernel embedded in the numerical model. An iterative coupling technique is adopted to solve the two-phase flow equations using a shared integration point memory implementation model. At each SFI time step, the efficiency iterative method for the transport equations is improved using a Quasi-Newton method with a simple but effective nonlinear acceleration. The numerical examples show that the proposed scheme is able to solve challenging coupledflow and transport problems.

The effect of drag‐reducing agents (DRAs) on fluid flows in straight pipes has been well documented. Key among these is the effect of DRAs on turbulence statistics (Reynolds shear stress, turbulence intensity, streamwise and wall‐normal velocity fluctuation among others). These primary effects result in secondary effects such as modification of mean velocity profile and reduction in frictional losses (drag reduction, DR). Interestingly, in curved pipe flows, the characteristic of flow is more complex due to secondary flow, wake effects and under‐developed flow characteristics. Therefore, a review of investigations on the effect of DRAs in curved pipe flows is presented in this paper. The paper highlights the difference between DR in straight and curved conduits as well as the interaction between DRAs and flow characteristics of curved pipe flows. Proposed mechanisms of DR, and factors that influence their effectiveness also received attention. It was shown that significant DR can be achieved in curved pipes. A review of various experimental results revealed that DR by additives in curved pipes is generally lower than in straight pipes but with certain similarities. It decreases with increase in curvature ratio and is more pronounced in the transition and turbulent flow regimes. Maximum DR asymptote differed between straight and curved pipes and between polymer and surfactant. Due to the limited studies in the area of DR for gas‐liquid flow in curved pipes, no definite conclusion could be drawn on the effect of DRAs on such flows. A number of questions remain such as physical interaction between molecules of DRA and flow features such as secondary flow streamlines and wakes. Hence, some research gaps have been identified with recommendations for areas of future researches.

The characteristics of flow configuration in pipes are very important in the oil industry due to its role in governing equipment design. In vertical risers, many flow configurations could be observed such as bubbly, slug, churn, and annular flow. In this project, two tomographic techniques have been applied simultaneously to the flow in a vertical riser: the Electrical Capacitance Tomography (ECT) technique and the Capacitance Wire Mesh Sensor (WMS) technique. The employed pipe diameter was 50mm and the superficial studied velocities were 0.06-3.0m/s for gas and 0.06-0.4m/s for oil. Several techniques have been used to analyze the output data of the two tomography techniques such as time series of cross-sectional averaged void fraction, Probability Density Function (PDF), image reconstruction, and liquid hold-up profile. The averaged void fractions were calculated from the output signal of the two measurement techniques and plotted as functions of the superficial velocity of the gas. The flow patterns were identified from the PDF of the averaged void fraction. In addition, it was found that both tomographic techniques are reliable in identifying the flow regimes in pipes.

In order to improve the inadequacy of the current research on oil droplet size distribution in aero-engine bearing chamber, the influence of oil droplet size distribution with the oil droplets coalescence and breakup is analyzed by using the computational fluid dynamics-population balance model (CFD-PBM). The Euler&ndash, Euler equation and population balance equation are solved in Fluent software. The distribution of the gas phase velocity field and the volume fraction of different oil droplet diameter at different time are obtained in the bearing chamber. Then, the influence of different initial oil droplet diameter, air, and oil mass flow on oil droplet size distribution is discussed. The result of numerical analysis is compared with the experiment in the literature to verify the feasibility and validity. The main results provide the following conclusions. At the initial stage, the coalescence of oil droplets plays a dominant role. Then, the breakup of larger diameter oil droplet appears. Finally, the oil droplet size distribution tends to be stable. The coalescence and breakup of oil droplet increases with the initial diameter of oil droplet and the air mass flow increasing, and the oil droplet size distribution changes significantly. With the oil mass flow increasing, the coalescence and breakup of oil droplet has little change and the variation of oil droplet size distribution is not obvious.

The characteristics of flow configuration in pipes are very important in the oil industry due to its role in governing equipment design. In vertical risers, many flow configurations could be observed such as bubbly, slug, churn, and annular flow. In this project, two tomographic techniques have been applied simultaneously to the flow in a vertical riser: the Electrical Capacitance Tomography (ECT) technique and the Capacitance Wire Mesh Sensor (WMS) technique. The employed pipe diameter was 50mm and the superficial studied velocities were 0.06-3.0m/s for gas and 0.06-0.4m/s for oil. Several techniques have been used to analyze the output data of the two tomography techniques such as time series of cross-sectional averaged void fraction, Probability Density Function (PDF), image reconstruction, and liquid hold-up profile. The averaged void fractions were calculated from the output signal of the two measurement techniques and plotted as functions of the superficial velocity of the gas. The flow patterns were identified from the PDF of the averaged void fraction. In addition, it was found that both tomographic techniques are reliable in identifying the flow regimes in pipes.

For environmental constraints, the new generations of aeronautical chambers, whose operation is based on a so-called "poor" combustion regime, are predisposed to the appearance of so-called thermo-acoustic instabilities. These instabilities, due to a coupling between the unsteady heat release q' and the acoustic pressure (p') or speed (v') oscillations, can lead to a strong amplification of the pressure and temperature oscillations and lead to the destruction of the chamber or engine extinction. An important factor in these phenomena is the phase difference between the acoustic oscillations and the flame response. To prevent the risks associated with these instabilities, preliminary simulations of combustion chamber behaviour are carried out. For this, two approaches can be considered. The first is based on two-phase and reactive LES simulations. The second is based on low order models based on the resolution of Helmholtz linearized equations and using a network type resolution method. The first approach requires a fine simulation of all the phenomena at the origin of the coupling and in particular the consideration of the behaviour of the liquid phase associating atomization, filming, droplets transport and evaporation. The second approach requires a model of the flame response to acoustic excitation. The work carried out in this thesis aims at providing detailed experimental data to feed these two approaches. It is thus composed of two parts. The first focuses on the unsteady behaviour of a liquid jet injected transversely to an acoustically excited air flow. This configuration makes it possible to reproduce the phenomena observed in a real injector. The measurements carried out enable the cyclic behaviour of the jet, its atomisation and the droplet spray thus formed to be analysed and to determine the characteristic times and velocities associated to the phenomena observed. The second part aims to study the non-linear behaviour of a two-phase flame obtained downstream of an aeronautical injector. These results are used to develop a flame response model called the "Flame Descriptive Function (FDF)", necessary for the implementation of low order models. This characterization first required the development of an original method for measuring heat release by chemiluminescence. The results obtained for two injector operating points and different excitation frequency and amplitude values highlighted the non-linear behaviour of the flame, which leads to saturation, at the origine of the limit cycles observed in real chambers.; Pour répondre aux contraintes environnementales, les nouvelles générations de chambre aéronautique, dont le fonctionnement est basé sur un régime de combustion dit « pauvre », sont prédisposées à l’apparition d’instabilités dites thermo-acoustiques. Ces instabilités dues à un couplage entre le dégagement de chaleur instationnaire q’ et les oscillations de pression (p’) ou de vitesse (v’) acoustique, peuvent entraîner une forte amplification des oscillations de pression et de température et conduire à une destruction de la chambre ou à un arrêt du moteur. Un critère important intervenant dans ces phénomènes est le déphasage entre les oscillations d’origine acoustique et la réponse de la flamme. Pour prévenir l’apparition des risques liés à ces instabilités, des simulations préalables du comportement des chambres de combustion sont réalisées. Pour cela deux approches peuvent être envisagées. La première, est basée sur des simulations LES diphasiques et réactives. La seconde repose sur des modèles bas ordres basés sur la résolution des équations linéarisées d’Helmholtz et utilisant une méthode de résolution de type réseau. La première approche nécessite une simulation fine de l’ensemble des phénomènes à l’origine du couplage et en particulier la prise en compte du comportement de la phase liquide associant atomisation, ruissellement, transport de gouttes et évaporation. La seconde approche nécessite quant à elle un modèle de réponse de flamme à une excitation acoustique. Le travail réalisé dans cette thèse a pour objectif de fournir des données expérimentales détaillées pour alimenter ces deux approches. Il est ainsi constitué de deux parties. La première se focalise sur le comportement instationnaire d’un jet liquide injecté transversalement à un écoulement d’air excité acoustiquement. Cette configuration permet de reproduire les phénomènes observés dans un injecteur réel. Les mesures réalisées permettent d’analyser le comportement cyclique du jet, de son atomisation et du brouillard de gouttes ainsi formé et de remonter à des temps et des vitesses caractéristiques des phénomènes observées. La seconde partie a pour objectif d’étudier le comportement non linéaire d’une flamme diphasique obtenue à l’aval d’un injecteur aéronautique. Ces résultats permettent d’élaborer un modèle de réponse de la flamme appelée « Fonction Descriptive de Flamme (FDF) », reliant les oscillations de dégagement de chaleur qu’à l’excitation acoustique u’, nécessaire à la mise en oeuvre des modèles de type bas ordres. Cette caractérisation a nécessité au préalable le développement d’une méthode original de mesure de dégagement de chaleur par chimiluminescence. Les résultats obtenus pour deux points de fonctionnement de l’injecteur et différentes valeurs de fréquence et amplitude d’excitation, ont mis en évidence le comportement non linéaire de la flamme engendrant un phénomène de saturation à l’origine des cycles limites observés sur des chambres réelles.

Blood coagulation is a critical and complex reaction that involves various chemical substances, such as prothrombin, fibrinogen, and fibrin. The process can be divided into three main steps, namely the formation of the prothrombin activator, conversion of prothrombin to thrombin, and conversion of fibrinogen to fibrin. In this study, an ANSYS simulation is carried out to determine the prothrombin time (PT) of blood, the chemical changes that occur during coagulation and the anticoagulation factor. The addition of deionized water to the microchannels before the addition of blood and reagents results in a two-phase flow. The evaluation of this two-phase flow is necessary, and dynamic simulations are required to determine the PT. The chemical rate constant and order of the chemical reaction are derived from the actual prothrombin time. Moreover, the genetic algorithms in PYTHON and ANSYS are used to estimate chemical reaction parameters for a 20 s PT. The blood and anticoagulant exhibit increased dynamic behavior in the microchannel. In addition, particles are added to the microchannel and the dynamic mesh method is used to simulate the flow behaviors of the red and white blood cells in the microchannel. The PTs for different volumes of blood are also reported.

The installation and operation of enhanced geothermal systems (EGS) involves many challenges. These challenges include the high cost and high risk associated with the investment capital, potential large working-fluid leakage, corrosion of equipment, and subsiding land. A super-long heat pipe can be used for geothermal exploitation to avoid these problems. In this paper, a high aspect-ratio heat pipe (30 m long, 17 mm in inner diameter) is installed vertically. Experiments are then carried out to study its heat-transfer performance and characteristics using several filling ratios of deionized water, different heating powers, and various cooling-water flowrates. The results show that the optimal filling-ratio is about 40% of the volume of the vaporizing section of the heat pipe. Compared with a conventional short heat pipe, the extra-long heat pipe experiences significant thermal vibration. The oscillation frequency depends on the heating power and working-fluid filling ratio. With increasing cooling-water flow rate, the heat-transfer rate of the heat pipe increases before it reaches a plateau. In addition, we investigate the heat-transfer performance of the heat pipe for an extreme working-fluid filling ratio, the results indicate that the lower part of the heat pipe is filled with vapor, which reduces the heat-transfer to the top part. Based on the experimental data, guidelines for designing a heat pipe that can be really used for the exploitation of earth-deep geothermal energy are analyzed.

Porous media surface roughness strongly influences the transport of solutes during drainage due to the formation of thick water films (capillary condensation) on the surface of the porous medium. For interfacially-reacted, water-based solutes, these water films increase both the solute production at the fluid-fluid interface, due to the increased number of fluid-fluid interfaces, and the loss of the solute due to retention in the water films. This study applied a pore-scale, direct numerical simulation with the phase-field method-based continuous solute transport model to simulate the reactive transport of the kinetic interfacial sensitive tracer. The study is implemented during primary drainage in a 2D slit with rough solid walls, where the fractal geometries of the solid surfaces were generated numerically. The moving interfacial area is found to be changing non-monotonically with the root mean square of surface roughness. With increasing root mean square roughness, the average film thickness increases linearly, whereas the film-associated interfacial area per smooth surface area converges to a value slightly larger than one. The retention of the solute mass produced by the moving meniscus in the water film is observed, and this is described by a film-associated mobile mass retention term. An implicit relation between the mobile interfacial area and the solute mass in flowing zones is found. Finally, it is found that the film-associated mobile mass retention term is linearly related to the root mean square roughness.

A plunging liquid jet is defined as a moving column of liquid passing through a gaseous headspace, air in our case, before impinging a free surface of receiving liquid pool. The mechanism of air entrainment due to plunging liquid jets is very complex and the complete mechanism of air entrainment is not fully understood so far. The present paper is an unsteady numerical simulation of air entrainment by water jet plunging, using the Volume Of Fluid (VOF) model. The piece wise linear interface construction algorithm (PLIC) for interface tracking is used, to describe the phase distributions of entirely immiscible air and liquid phases. The aim of this work is to investigate the performance and accuracy of the VOF method in predicting the initial impact between the descending jet and water free surface, air entrainment and the developing flow region under free surface. Three scale models based on geometric similarities (Froude number and dimensionless free jet length) are used for validation according to Chanson (2004) experience. The simulations show with accuracy, the air cavity formation steps, caused by the initial jet impact, its deep stretching under the pool free surface, until breakdown due to the shear created by a toroidal vortex. In terms of, air entrainment estimation, bubble dispersion and radial distribution of air volume fraction, large-scale models present a good agreement with the experience. However, for the smallest scale model, the results lead to suggest that air entrainment is governed by more parameters than the geometric similarities.

The modeling of transfer processes is a step in the generalization and interpretation of experimental data on heat transfer. The developed two-dimensional model is based on a homogeneous mixture model for boiling water flow in a microchannel with a new evaporation submodel. The outcome of the simulation is the distribution of velocity, void fraction and temperature profiles in the microchannel. The predicted temperature profile is consistent with the experimental literature data.

In this paper, we propose a two-stage method for petroleum reservoir simulation. The method uses two models with different degrees of detailing to describe hydrodynamic processes of different space-time scales. At the first stage, the global dynamics of the energy state of the deposit and reserves is modeled (characteristic scale of such changes is km / year). The two-phase flow equations in the model of global dynamics operate with smooth averaged pressure and saturation fields, and they are solved numerically on a large computational grid of super-elements with a characteristic cell size of 200-500 m. The tensor coefficients of the super-element model are calculated using special procedures of upscaling of absolute and relative phase permeabilities. At the second stage, a local refinement of the super-element model is constructed for calculating small-scale processes (with a scale of m / day), which take place, for example, during various geological and technical measures aimed at increasing the oil recovery of a reservoir. Then we solve the two-phase flow problem in the selected area of the measure exposure on a detailed three-dimensional grid, which resolves the geological structure of the reservoir, and with a time step sufficient for describing fast-flowing processes. The initial and boundary conditions of the local problem are formulated on the basis of the super-element solution. This approach allows us to reduce the computational costs in order to solve the problems of designing and monitoring the oil reservoir. To demonstrate the proposed approach, we give an example of the two-stage modeling of the development of a layered reservoir with a local refinement of the model during the isolation of a water-saturated high-permeability interlayer. We show a good compliance between the locally refined solution of the super-element model in the area of measure exposure and the results of numerical modeling of the whole history of reservoir development on a detailed grid.

Gas- Liquid flows are by far the most important type of multiphase flow. This can be attributed to the wide range of industrial applications that the gas-liquid flow is discerned in. Popular examples of Gas-liquid flows are oil-gas mixtures, evaporators, boilers, condensers, refrigeration and cryogenics. The measurement of the liquid film thickness in two phase flows is prominent in various heat and mass transfer applications such as in boilers. To determine the thin film thickness is the aim of this study. A glass tube of diameter 4.7 mm is used for conducting the experiment and a laser pointer is used to obtain an image pattern on the screen. Using the principles of Optics, a method has been proposed to determine the thin film thickness and also to characterize the different types of flow. The thin film thickness obtained in the proposed method is validated using Image Processing.

For environmental constraints, the new generations of aeronautical chambers, whose operation is based on a so-called "poor" combustion regime, are predisposed to the appearance of so-called thermo-acoustic instabilities. These instabilities, due to a coupling between the unsteady heat release q' and the acoustic pressure (p') or speed (v') oscillations, can lead to a strong amplification of the pressure and temperature oscillations and lead to the destruction of the chamber or engine extinction. An important factor in these phenomena is the phase difference between the acoustic oscillations and the flame response. To prevent the risks associated with these instabilities, preliminary simulations of combustion chamber behaviour are carried out. For this, two approaches can be considered. The first is based on two-phase and reactive LES simulations. The second is based on low order models based on the resolution of Helmholtz linearized equations and using a network type resolution method. The first approach requires a fine simulation of all the phenomena at the origin of the coupling and in particular the consideration of the behaviour of the liquid phase associating atomization, filming, droplets transport and evaporation. The second approach requires a model of the flame response to acoustic excitation. The work carried out in this thesis aims at providing detailed experimental data to feed these two approaches. It is thus composed of two parts. The first focuses on the unsteady behaviour of a liquid jet injected transversely to an acoustically excited air flow. This configuration makes it possible to reproduce the phenomena observed in a real injector. The measurements carried out enable the cyclic behaviour of the jet, its atomisation and the droplet spray thus formed to be analysed and to determine the characteristic times and velocities associated to the phenomena observed. The second part aims to study the non-linear behaviour of a two-phase flame obtained downstream of an aeronautical injector. These results are used to develop a flame response model called the "Flame Descriptive Function (FDF)", necessary for the implementation of low order models. This characterization first required the development of an original method for measuring heat release by chemiluminescence. The results obtained for two injector operating points and different excitation frequency and amplitude values highlighted the non-linear behaviour of the flame, which leads to saturation, at the origine of the limit cycles observed in real chambers., Pour répondre aux contraintes environnementales, les nouvelles générations de chambre aéronautique, dont le fonctionnement est basé sur un régime de combustion dit « pauvre », sont prédisposées à l’apparition d’instabilités dites thermo-acoustiques. Ces instabilités dues à un couplage entre le dégagement de chaleur instationnaire q’ et les oscillations de pression (p’) ou de vitesse (v’) acoustique, peuvent entraîner une forte amplification des oscillations de pression et de température et conduire à une destruction de la chambre ou à un arrêt du moteur. Un critère important intervenant dans ces phénomènes est le déphasage entre les oscillations d’origine acoustique et la réponse de la flamme. Pour prévenir l’apparition des risques liés à ces instabilités, des simulations préalables du comportement des chambres de combustion sont réalisées. Pour cela deux approches peuvent être envisagées. La première, est basée sur des simulations LES diphasiques et réactives. La seconde repose sur des modèles bas ordres basés sur la résolution des équations linéarisées d’Helmholtz et utilisant une méthode de résolution de type réseau. La première approche nécessite une simulation fine de l’ensemble des phénomènes à l’origine du couplage et en particulier la prise en compte du comportement de la phase liquide associant atomisation, ruissellement, transport de gouttes et évaporation. La seconde approche nécessite quant à elle un modèle de réponse de flamme à une excitation acoustique. Le travail réalisé dans cette thèse a pour objectif de fournir des données expérimentales détaillées pour alimenter ces deux approches. Il est ainsi constitué de deux parties. La première se focalise sur le comportement instationnaire d’un jet liquide injecté transversalement à un écoulement d’air excité acoustiquement. Cette configuration permet de reproduire les phénomènes observés dans un injecteur réel. Les mesures réalisées permettent d’analyser le comportement cyclique du jet, de son atomisation et du brouillard de gouttes ainsi formé et de remonter à des temps et des vitesses caractéristiques des phénomènes observées. La seconde partie a pour objectif d’étudier le comportement non linéaire d’une flamme diphasique obtenue à l’aval d’un injecteur aéronautique. Ces résultats permettent d’élaborer un modèle de réponse de la flamme appelée « Fonction Descriptive de Flamme (FDF) », reliant les oscillations de dégagement de chaleur qu’à l’excitation acoustique u’, nécessaire à la mise en oeuvre des modèles de type bas ordres. Cette caractérisation a nécessité au préalable le développement d’une méthode original de mesure de dégagement de chaleur par chimiluminescence. Les résultats obtenus pour deux points de fonctionnement de l’injecteur et différentes valeurs de fréquence et amplitude d’excitation, ont mis en évidence le comportement non linéaire de la flamme engendrant un phénomène de saturation à l’origine des cycles limites observés sur des chambres réelles.

We present a theoretical framework for immiscible incompressible two-phase flow in homogeneous porous media that connects the distribution of local fluid velocities to the average seepage velocities. By dividing the pore area along a cross-section transversal to the average flow direction up into differential areas associated with the local flow velocities, we construct a distribution function that allows us not only to re-establish existing relationships between the seepage velocities of the immiscible fluids, but also to find new relations between their higher moments. We support and demonstrate the formalism through numerical simulations using a dynamic pore-network model for immiscible two-phase flow with two- and three-dimensional pore networks. Our numerical results are in agreement with the theoretical considerations., 12 pages, 5 figures

Air-core&ndash, liquid-ring (ACLR) atomization presents a specific type of internal mixing pneumatic atomization. It can be used for disintegration of high viscous feed liquids into small droplets at relatively low gas consumptions. However, the specific principle of ACLR atomization is still under research and no guidelines for process and atomizer design are available. Regarding literature on pre-filming atomizers, it can be hypothesized for ACLR atomization that the liquid film thickness inside the exit orifice of the atomizer, as well as the resulting spray droplet sizes decrease with increasing air-to-liquid ratio (ALR) and decreasing feed viscosity. In this study, the time dependent liquid film thickness inside the exit orifice of the atomizer was predicted by means of computational fluid dynamics (CFD) analysis. Results were compared to high speed video images and correlated to measured spray droplet sizes. In conclusion, the hypothesis could be validated by simulation and experimental data, however, at high viscosity and low ALR, periodic gas core breakups were detected in optical measurements. These breakups could not be predicted in CFD simulations, as the simplification of an incompressible gas phase was applied in order to reduce computational costs and time. Nevertheless, the presented methods show good potential for improvement of atomizer geometry and process design as well as for further investigation of the ACLR atomization principle.

Thermographic PIV is a promising technique that enables simultaneous temperature and velocity imaging in flows with intentional seeded phosphor particles. This is highly attractive to researchers in fluid mechanics and combustion, as it directly visualizes the heat and mass transfer process in turbulent flows/flames. However, three problems for this technique are: (a) it requires two lasers and three cameras running simultaneously, making it a high-cost technique; (b) several recent studies reported the multiple scattering effects for gas-phase phosphor thermometry, which may severely bias the temperature measurement for certain flow configurations; and (c) the phosphorescent emission disappears at high temperature due to thermal quenching, which limits the temperature measurements to mostly non-reacting cases below 1100 K. This dissertation is aimed at providing solutions to the issues described above. To reduce the cost of the current thermographic PIV setup, a simplified version is proposed which uses a double-pulsed laser with UV capacity and two CCD cameras operating in the double-frame mode. This experiment proves that, apart from Mie scattering, phosphorescence image pairs can also be used to perform cross-correlation and calculate the vector field. Therefore both velocity and temperature field can be extracted from phosphorescence emissions excited by a single laser (UV-PIV). Thermographic PIV with this simplified setup is demonstrated on an electrically heated air jet, and 3 K accuracy is achieved in the core region of the jet, by comparing with a thermocouple scan. A novel calibration process is also proposed to eliminate the influence of non-uniform laser profile on the temperature measurements. The same technique is also applied to visualize heat transfer in an impinging jet. By correlating the instantaneous gaseous temperature fields with the averaged \textit{Nu} profiles derived from the wall temperature, the role of vortical structures in heat transfer is investigated and discussed. During the application of thermographic PIV, the problem of multiple scattering emerged and has been reported by several studies, especially for cases where an excessive seeding is used. Multiple scattering was found to reduce the spatial resolution and bias the temperature measurements. A recent study demonstrated that the Structured Laser Illumination Planar Imaging (SLIPI) technique could effectively remove multiple scattering and near-wall effects from the LIP image. However, it is well known that the emission spectrum of some most commonly used thermographic phosphors is sensitive to the changes in laser fluence, whilst SLIPI intentionally modulates the laser profiles and thus may bring in uncertainty into the temperature retrieval. This has yet not been discussed in the literature. In this dissertation, a numerical analysis is conducted, by generating artificial laser induced phosphorescence images, to investigate the effects that SLIPI may have on the temperature measurements. To implement simultaneous temperature and velocity measurements in flames, an entirely new approach of thermographic PIV is proposed in this dissertation. This new version is based on laser-induced incandescence (LII), rather than phosphorescence. Submicron black particles are seeded into a flame, and further heated by a high-energy top-hat laser sheet to several thousands kelvin. The particle temperature $T_\mathrm{p}$ can be measured by two-color pyrometry, where the temperature increase $\Delta T$ due to laser absorption can be determined by conducting an {\em in-situ} calibration. Thus the local temperature $T_0$ can be indirectly determined by subtracting $\Delta T$ from $T_\mathrm{p}$. The same particle can also be used as PIV tracers. The concept and fundamentals of this new thermographic PIV approach are described in this thesis. The combination of LII and PIV is also applied as a tool to measure the gas-phase velocity in a two-phase flow, which is a canonical problem for multiphase flow studies., Part of the research presented in this thesis was funded by University Technology Malaysia (UTM) under grant number RG84263

A numerical method for simulating transient flows of gas-liquid mixtures is proposed. The mathematical model, established for a suspension of gas bubbles in liquid, includes an equation taking into account the relative velocity between the gas and liquid. A numerical technique based on the Mac Cormack scheme combined with the method of characteristics is presented. Theoretical results for transients initiated by a rapid closing valves are compared with measurements. A good agreement is found particularly for large values of initial dissolved gas concentration.

The paper explores a tandem configuration of three-blade impellers in a stirred reactor. The working fluid is a liquid-solid mixture and the stirring mechanism fitted with the two impellers must prevent the sedimentation of solid particles while homogenously dispersing them in the bulk liquid. The present numerical investigation, performed with the expert software Ansys® Fluent, Release 16, employs the Eulerian multiphase model along with the RNG k–ε turbulence model to simulate the free-surface liquid–solid flows in the baffled stirred reactor. A sliding mesh approach is used to model the impellers rotation. The tandem configuration is clearly superior to a single impeller, while the existing electrical motor that drives the stirring mechanism still provides the necessary power.

For stationary gas turbines, the injection of water sprays into the compressor inlet is used to increase the power output, which can be used for rapid correction of power fluctuations appearing in power supply systems with today’s increased use of wind and solar energy. However, to fully utilize this technique a comprehensive understanding of the underlying phenomena is needed. An inhouse CFD program was used at Institute of Aerospace Thermodynamics (ITLR) Stuttgart modeling a variety of two-phase phenomena which was validated on the transonic wind tunnel at Helmut Schmidt University (HSU) Hamburg. The present paper focuses on the water film on the blades formed by water deposition of impinged droplets. Experimental results using a reflective shadowgraphy method reveal the wall film pattern on the blade without disturbing the flow. A numerical model is presented predicting the position of film breakup based on the superposition of a small perturbation of the film height. The onset of film breakup is predicted to be at the position in which the perturbation is not dampened by the acting forces. The film breakup position is analyzed experimentally and numerically for three different water loads. The experimental analysis shows that the onset of film breakup is almost independent of the water load. The numerical model shows the same trends and indicates a film breakup at the same position.

The paper presents a 2D upward infiltration experiment performed on a model porous medium consisting of fine sand background with two inclusions made of coarser sands. The purpose of the experiment was to investigate the effects of structural air trapping, which occurs during infiltration as a result of heterogeneous material structure. The experiment shows that a significant amount of air becomes trapped in each of the inclusions. Numerical simulations were carried out using the two-phase water-air flow model and the Richards equation. The experimental results can be reproduced with good accuracy only using a two-phase flow model, which accounts for both structural and pore-scale trapping. On the other hand, the Richards equation was not able to represent the structural trapping caused by material heterogeneity.

Water-hammer phenomena are of strong interest in a number of different industrial fields, amongst which the space industry. Here the priming of feedlines during start-up of an engine as well as the rapid closing of valves upon shutdown may lead to pressure peaks symptomatic of a water-hammer wave. Test benches used to conduct tests on future as well as current engines are also sensitive to water-hammer waves traveling along their feedlines. To enhance the understanding of water-hammer, we investigated different configurations and their influence on the wave shape in the frequency domain. The configurations feature a coiled pipe setup with a support structure and without a support structure. Two other phenomena will be presented. We found a beat phenomenon which is likely to be the so called Poisson-coupling beat. Finally we will show that the second water-hammer peak can reach pressures a lot higher than the first peak by additive interference of the primary and secondary water-hammer wave.

International audience; I present a fast algorithm for modeling invasion percolation (IP) with trapping (TIP). IP is a numerical algorithm that models quasi-static (i.e. slow) fluid invasion in porous media. Trapping occurs when the invading fluid (that is injected) forms continuous surfaces surrounding patches of the displaced fluid (that is assumed incompressible and originally saturates the invaded medium). In TIP, the invading fluid is not allowed to enter the trapped patches. I demonstrate that TIP can be modeled in two steps: (1) Run an IP simulation without trapping (NTIP). (2) Identify the sites that invaded trapped regions and remove them from the chronological list of sites invaded in NTIP. Fast algorithms exist for solving NTIP. The focus of this paper is to propose an efficient solution for step (2). I show that it can be solved using a disjoint set data structure and going backward in time, i.e. by un-invading all sites invaded in NTIP in reverse order. Time reversal of the invasion greatly reduces the computational complexity for the identification of trapped sites as one only needs to investigate sites neighbor to the latest invaded/un-invaded site. This differs from traditional approaches where trapping is performed in real time, i.e. as the IP simulation is running, and where it is sometimes necessary to investigate the whole lattice to identify newly trapped regions. With the proposed algorithm, the total computational time for the identification and the removal of trapped sites goes as O(N), where N is the total number of sites in the lattice.