Dry Powder Inhalers (DPIs) have great potential in pulmonary drug delivery; the granular powder, used as active ingredient in DPIs, is ozone friendly and the operation of DPIs ensures coordination between dose release and patient inhalation. However, the powder fluidisation mechanisms are poorly understood which leads to low efficiency of DPIs with 10-35 % of the dose reaching the site of action. The main aim of this thesis is to study the hydrodynamics of powder fluidisation in DPIs, using experimental and computational approaches. An experimental test rig was developed to replicate the process of transient powder fluidisation in an impinging air jet configuration. The powder fluidisation chamber was scaled up resulting in a two dimensional particle flow prototype, which encloses 3.85 mm glass beads. Using optical image processing techniques, individual particles were detected and tracked throughout the experimental time and domain. By varying the air flow rate to the test section, two particle fluidisation regimes were studied. In the first fluidisation regime, the particle bed was fully fluidised in less than 0.25 s due to the strong air jet. Particle velocity vectors showed strong convective flow with no evidence of diffusive motion triggered by inter-particle collisions. In the second fluidisation regime, the particle flow experienced two stages. The first stage showed strong convective flow similar to the first fluidisation regime, while the second stage showed more complex particle flow with collisional and convective flow taking place on the same time and length scales. The continuum Two Fluid Model (TFM) was used to solve the governing equations of the coupled granular and gas phases for the same experimental conditions. Sub-models for particle-gas and particle-particle interactions were used to complete the model description. Inter-particle interactions were resolved using models based on the kinetic theory of granular flow for the rapid flow regime and models based on soil mechanics for the frictional regime. Numerical predictions of the first fluidisation regime showed that the model should incorporate particle-wall friction and minimise diffusion, simultaneously. Ignoring friction resulted in fluidisation timing mismatch, while increasing the diffusion resulted in homogenous particle fluidisation in contrast to the aggregative convective fluidisation noticed in the experiments. Numerical predictions of the second fluidisation regime agreed well with the experiments for the convection dominated first stage of flow up to 0.3 s. However, later stages of complex particle flow showed qualitative discrepancies between the experimental and the computational approaches suggesting that current continuum granular models need further development. The findings of the present thesis have contributed towards better understanding of the mechanics of particle fluidisation and dense multiphase flow in DPI in particular, and particle bed fluidisation using impinging air jet in general. The use of TFM for predicting high speed convective granular flows, such as those in DPIs, is promising. Further studies are needed to investigate the form of particle-particle interactions within continuum granular flow models.

<p>In this thesis the two-fluid (Eulerian/Eulerian) formulation for dispersed two-phase flow is considered. Closure laws are needed for this type of models. We investigate both empirically based relations, which we refer to as a nongranular model, and relations obtained from kinetic theory of dense gases, which we refer to as a granular model. For the granular model, a granular temperature is introduced, similar to thermodynamic temperature. It is often assumed that the granular energy is in a steady state, such that an algebraic granular model is obtained. </p><p>The inviscid non-granular model in one space dimension is known to be conditionally well-posed. On the other hand, the viscous formulation is locally in time well-posed for smooth initial data, but with a medium to high wave number instability. Linearizing the algebraic granular model around constant data gives similar results. In this study we consider a couple of issues. </p><p>First, we study the long time behavior of the viscous model in one space dimension, where we rely on numerical experiments, both for the non-granular and the algebraic granular model. We try to regularize the problem by adding second order artificial dissipation to the problem. The simulations suggest that it is not possible to obtain point-wise convergence using this regularization. Introducing a new measure, a concept of 1-D bubbles, gives hope for other convergence than point-wise. </p><p>Secondly, we analyse the non-granular formulation in two space dimensions. Similar results concerning well-posedness and instability is obtained as for the non-granular formulation in one space dimension. Investigation of the time scales of the formulation in two space dimension suggests a sever restriction on the time step, such that explicit schemes are impractical. </p><p>Finally, our simulation in one space dimension show that peaks or spikes form in finite time and that the solution is highly oscillatory. We introduce a model problem to study the formation and smoothness of these peaks.</p>

[pt] Escoamentos intermitentes bifásicos são caracterizados pela sucessão de golfadas de líquido separadas por bolhas de diferentes tamanhos, escoando com frequência variável. A previsão deste tipo de escoamento é muito importante, uma vez que o mesmo pode ser encontrado em diversas aplicações industriais. No presente trabalho, é realizado um estudo do regime intermitente em tubulações verticais, utilizando o Modelo de Dois Fluidos uni-dimensional, juntamente como o método de Volumes Finitos. O Modelo de Dois Fluidos uni-dimensional requer a inclusão de diversas relações de fechamento para as fases líquida e gasosa. Estas relações devem representar realisticamente o fenômeno físico de interesse, e as equações resultantes devem ser bem postas. No presente trabalho, duas relações de fechamento foram consideradas: salto de pressão devido à curvatura da interface e parâmetro de distribuição de fluxo de quantidade de movimento. A presença do salto de pressão não se mostrou significativa, enquanto que o parâmetro relacionado a distribuição da fase líquida ampliou a região em que o sistema de equações é bem posto. Para os casos analisados, o parâmetro de distribuição da fase líquida apresentou influência nas características do escoamento. As principais grandezas do regime estatisticamente permanente, como comprimento e velocidade de translação da golfada e da bolha, foram comparadas com dados experimentais disponíveis na literatura, apresentando boa concordância. / [en] Intermittent two phase flows are characterized by a succession of liquid slugs separated by bubbles of different sizes, with varying frequency. The prediction of this type of flow is very important, since it can be found in several industrial applications. In the present work, studies of intermittent flows in vertical pipes are performed, employing the Two Fluid Model along with the Finite Volume method. The one-dimensional Two Fluid Model requires the inclusion of several closure relations for both gas and liquid phases. These relations should realistically represent the physical phenomenon of interest, and the resulting equations should be well posed. In this work, two closure relations were considered: pressure jump due to the interface curvature and momentum flux distribution parameter. The inclusion of the pressure jump did not present a significant influence, whereas the momentum flux parameter of the liquid phase increased the region in which the system of equations is well posed. For the cases analyzed, the momentum flux parameter of the liquid phase affected the flow characteristics. The main statistical slug quantities, such as length and translational speed of the bubble and slug, were compared with experimental data available in the literature, showing good agreement.

[pt] Escoamentos bifásicos no regime de golfadas são caracterizados pela alternância de pacotes de líquido e grandes bolhas de gás na tubulação, sendo associados a altas perdas de carga, além de trazer uma indesejada intermitência aos escoamentos. O desenvolvimento do regime de golfadas em tubulações horizontais se dá a partir do escoamento estratificado em decorrência de dois fatores: do crescimento natural de pequenas perturbações (por um mecanismo de instabilidade do tipo Kelvin-Helmholtz) ou devido à acumulação de líquido causada por mudanças de inclinação no perfil do duto. O presente trabalho consiste da simulação numérica do surgimento das golfadas em ambas as situações descritas acima, assim como do subseqüente desenvolvimento do escoamento neste padrão para um regime estatisticamente permanente. A previsão do escoamento é obtida utilizando-se uma formulação unidimensional baseada no Modelo de Dois Fluidos. Parâmetros médios das golfadas (comprimento, velocidade e freqüência) são comparados com estudos numéricos e experimentais da literatura, obtendo-se uma concordância bastante satisfatória, especialmente dada a simplicidade de uma formulação unidimensional. / [en] Slug flow is a two-phase flow pattern which is characterized by the periodic presence of packs of liquid and long bubbles in the tube, associated with high pressure-drops and an often undesired intermittency in the system. The development of the slug pattern in horizontal pipes is caused by two reasons: the natural growth of small disturbancies at the interface (by a Kelvin-Helmholtz instability mechanism) or the liquid accumulation at valleys of hilly terrain pipelines with sections of different inclinations. The present work consists of the numerical simulation of the onset of slugging in both situations, as well as the subsequent development of statistically steady slug flow in the pipe. The prediction of the flow is obtained through a one- dimensional formulation based on the Two-Fluid Model. Averaged slug parameters (length, velocity and frequency) are compared with previous numerical studies and experimental correlations avaiable in the literature, and a very satisfactrory agreement is obtained, specially given the simplicity of a one dimensional formulation.

In this thesis the two-fluid (Eulerian/Eulerian) formulation for dispersed two-phase flow is considered. Closure laws are needed for this type of models. We investigate both empirically based relations, which we refer to as a nongranular model, and relations obtained from kinetic theory of dense gases, which we refer to as a granular model. For the granular model, a granular temperature is introduced, similar to thermodynamic temperature. It is often assumed that the granular energy is in a steady state, such that an algebraic granular model is obtained. The inviscid non-granular model in one space dimension is known to be conditionally well-posed. On the other hand, the viscous formulation is locally in time well-posed for smooth initial data, but with a medium to high wave number instability. Linearizing the algebraic granular model around constant data gives similar results. In this study we consider a couple of issues. First, we study the long time behavior of the viscous model in one space dimension, where we rely on numerical experiments, both for the non-granular and the algebraic granular model. We try to regularize the problem by adding second order artificial dissipation to the problem. The simulations suggest that it is not possible to obtain point-wise convergence using this regularization. Introducing a new measure, a concept of 1-D bubbles, gives hope for other convergence than point-wise. Secondly, we analyse the non-granular formulation in two space dimensions. Similar results concerning well-posedness and instability is obtained as for the non-granular formulation in one space dimension. Investigation of the time scales of the formulation in two space dimension suggests a sever restriction on the time step, such that explicit schemes are impractical. Finally, our simulation in one space dimension show that peaks or spikes form in finite time and that the solution is highly oscillatory. We introduce a model problem to study the formation and smoothness of these peaks. / QC 20101018

In this dissertation, an experimental and numerical study of dense coarse solids-liquid flows has been performed. The experimental work mainly involved pressure drop measurements in a vertical flow loop. A limited number of measurements of solids velocity profiles were also obtained in the upward flow section of the flow loop. The numerical work involved simulations of coarse particles-in-water flows in vertical and horizontal pipes. The vertical flow simulations were performed using the commercial CFD software, ANSYS CFX-4.4, while ANSYS CFX-10 was used to simulate the flows in the horizontal pipes. The simulations were performed to investigate the applicability of current physically-based models to very dense coarse-particle flows.<p> In the experimental study, measurements of pressure drop and local solids velocity profiles were obtained. The experiments were conducted in a 53 mm diameter vertical flow loop using glass beads of 0.5 mm and 2.0 mm diameter solids for concentration up to 45%. The liquid phase was water. The measured pressure drop exhibited the expected dependence on bulk velocity and solids mean concentration. The wall shear stress was determined by subtracting the gravitational contribution from the measured pressure drop. For flow with the 0.5 mm particles at high bulk velocities, the values of the wall shear stress were essentially similar for each concentration in the upward flow sections but more variation, indicating the effect of concentration, was noted in the downward flow section. At lower bulk velocities, the wall shear stresses with the 0.5 mm glass beads-water flow showed a dependence on concentration in both test sections. This was attributed to an increase in the slip velocity. For the large particle (2.0 mm glass beads), similar observations were made but the effect of concentration was much less in the upward test section. In the downward test section, the wall shear stress for the flow of the 2.0 mm glass beads increased by almost a constant value for the bulk velocities investigated. The solids velocity profiles showed that the solids velocity gradient is large close to the wall. In addition, the solids velocity profiles indicated that the slip velocity increased at lower velocities due to increase in the bulk concentration in the upward flow section.<p> For the vertical flow simulations, different physical models based on the kinetic theory of granular flows were programmed and implemented in ANSYS CFX-4.4. These models, referred to as the kf-ef-ks-es, kf-ef-ks-es-Ts and kf-ef-ks-kfs models, were investigated by focusing on the closure laws for the solids-phase stress. The treatment of the granular temperature Ts depends on whether small- or large-scale fluctuating motion of the particles is considered. The models were implemented via user-Fortran routines. The predicted results were compared with available experimental results. The predicted solids-phase velocity profiles matched the measured data quite well close to the pipe wall but over-predicted it in the core region. The solids concentration, on the other hand, was significantly under-predicted for concentrations higher than 10%. Variations in the predictions of the phasic turbulent kinetic energy and the eddy viscosity were noted; the effect of solids concentration on them was mixed. A general conclusion drawn from the work is that a more accurate model is required for accurate and consistent prediction of coarse particle flows at high concentrations (less than 10%). In a related study, attention was given to wall boundary conditions again focusing on the effect of the solids-phase models at the wall. Comparison between numerical predictions, using some of the existing wall boundary condition models for the solids phase in particulate flows, with experimental results indicated that the physical understanding of the influence of the fluid and solids-phase on each other and their effect on frictional head loss is far from complete. The models investigated failed to reproduce the experimental results. At high solids concentration, it was apparent from the present study that the no-slip and free-slip wall boundary conditions are not appropriate for liquid-solid flows.<p> For the horizontal flow case, three-dimensional simulations were performed with a focus on the velocity and concentration distributions. Medium and coarse sand-in-water flows in three pipe diameters were considered to investigate the default solids stress models in ANSYS CFX-10. Simulations were performed for three cases by considering: 1) no additional solids-phase stress, i.e. no model for Ts; 2) a zero equation, and 3) an algebraic equilibrium model for the granular temperature. The model predictions were compared to experimental results. The effect of particle size, solids-phase concentration, and pipe diameter was explored using the algebraic equilibrium model. All the cases for the models considered exhibited the characteristic features of horizontal coarse particle slurry flows. The zero equation and the algebraic equilibrium model for the granular temperature produced similar results that were not significantly different from the prediction obtained when no solids-phase stress was considered. The comparison with experimental results was mixed. Locally, the measured solids-phase velocity distributions were over-predicted, whereas the solids concentration was reasonably reproduced in the core of all the pipes. The concentration at the bottom and top walls were over-, and under-predicted, respectively. This was attributed to the inappropriate phasic wall boundary condition models available.

No description available.

In this dissertation, an experimental and numerical study of dense coarse solids-liquid flows has been performed. The experimental work mainly involved pressure drop measurements in a vertical flow loop. A limited number of measurements of solids velocity profiles were also obtained in the upward flow section of the flow loop. The numerical work involved simulations of coarse particles-in-water flows in vertical and horizontal pipes. The vertical flow simulations were performed using the commercial CFD software, ANSYS CFX-4.4, while ANSYS CFX-10 was used to simulate the flows in the horizontal pipes. The simulations were performed to investigate the applicability of current physically-based models to very dense coarse-particle flows.<p> In the experimental study, measurements of pressure drop and local solids velocity profiles were obtained. The experiments were conducted in a 53 mm diameter vertical flow loop using glass beads of 0.5 mm and 2.0 mm diameter solids for concentration up to 45%. The liquid phase was water. The measured pressure drop exhibited the expected dependence on bulk velocity and solids mean concentration. The wall shear stress was determined by subtracting the gravitational contribution from the measured pressure drop. For flow with the 0.5 mm particles at high bulk velocities, the values of the wall shear stress were essentially similar for each concentration in the upward flow sections but more variation, indicating the effect of concentration, was noted in the downward flow section. At lower bulk velocities, the wall shear stresses with the 0.5 mm glass beads-water flow showed a dependence on concentration in both test sections. This was attributed to an increase in the slip velocity. For the large particle (2.0 mm glass beads), similar observations were made but the effect of concentration was much less in the upward test section. In the downward test section, the wall shear stress for the flow of the 2.0 mm glass beads increased by almost a constant value for the bulk velocities investigated. The solids velocity profiles showed that the solids velocity gradient is large close to the wall. In addition, the solids velocity profiles indicated that the slip velocity increased at lower velocities due to increase in the bulk concentration in the upward flow section.<p> For the vertical flow simulations, different physical models based on the kinetic theory of granular flows were programmed and implemented in ANSYS CFX-4.4. These models, referred to as the kf-ef-ks-es, kf-ef-ks-es-Ts and kf-ef-ks-kfs models, were investigated by focusing on the closure laws for the solids-phase stress. The treatment of the granular temperature Ts depends on whether small- or large-scale fluctuating motion of the particles is considered. The models were implemented via user-Fortran routines. The predicted results were compared with available experimental results. The predicted solids-phase velocity profiles matched the measured data quite well close to the pipe wall but over-predicted it in the core region. The solids concentration, on the other hand, was significantly under-predicted for concentrations higher than 10%. Variations in the predictions of the phasic turbulent kinetic energy and the eddy viscosity were noted; the effect of solids concentration on them was mixed. A general conclusion drawn from the work is that a more accurate model is required for accurate and consistent prediction of coarse particle flows at high concentrations (less than 10%). In a related study, attention was given to wall boundary conditions again focusing on the effect of the solids-phase models at the wall. Comparison between numerical predictions, using some of the existing wall boundary condition models for the solids phase in particulate flows, with experimental results indicated that the physical understanding of the influence of the fluid and solids-phase on each other and their effect on frictional head loss is far from complete. The models investigated failed to reproduce the experimental results. At high solids concentration, it was apparent from the present study that the no-slip and free-slip wall boundary conditions are not appropriate for liquid-solid flows.<p> For the horizontal flow case, three-dimensional simulations were performed with a focus on the velocity and concentration distributions. Medium and coarse sand-in-water flows in three pipe diameters were considered to investigate the default solids stress models in ANSYS CFX-10. Simulations were performed for three cases by considering: 1) no additional solids-phase stress, i.e. no model for Ts; 2) a zero equation, and 3) an algebraic equilibrium model for the granular temperature. The model predictions were compared to experimental results. The effect of particle size, solids-phase concentration, and pipe diameter was explored using the algebraic equilibrium model. All the cases for the models considered exhibited the characteristic features of horizontal coarse particle slurry flows. The zero equation and the algebraic equilibrium model for the granular temperature produced similar results that were not significantly different from the prediction obtained when no solids-phase stress was considered. The comparison with experimental results was mixed. Locally, the measured solids-phase velocity distributions were over-predicted, whereas the solids concentration was reasonably reproduced in the core of all the pipes. The concentration at the bottom and top walls were over-, and under-predicted, respectively. This was attributed to the inappropriate phasic wall boundary condition models available.

During the production and transportation of oil and gas, flow assurance issues may occur due to the solid deposits that are formed and carried by the flowing fluid. Solid deposition may cause serious damage and possible failure to production equipment in the flow lines. The major flow assurance problems that are faced in the fields are concerned with asphaltene, wax and scale deposition, as well as hydrate formations. Hydrates, wax and asphaltene deposition are mostly addressed in deep-water environments, where fluid flows through a long path with a wide range of pressure and temperature variations (Hydrates are generated at high pressure and low temperature conditions). In fact, a large change in the thermodynamic condition of the fluid yields phase instability and triggers solid deposit formations. In contrast, scales are formed in aqueous phase when some incompatible ions are mixed. Among the different flow assurance issues in hydrocarbon reservoirs, asphaltenes are the most complicated one. In fact, the difference in the nature of these molecules with respect to other hydrocarbon components makes this distinction. Asphaltene molecules are the heaviest and the most polar compounds in the crude oils, being insoluble in light n-alkenes and readily soluble in aromatic solvents. Asphaltene is attached to similarly structured molecules, resins, to become stable in the crude oils. Changing the crude oil composition and increasing the light component fractions destabilize asphaltene molecules. For instance, in some field situations, CO₂ flooding for the purpose of enhanced oil recovery destabilizes asphaltene. Other potential parameters that promote asphaltene precipitation in the crude oil streams are significant pressure and temperature variation. In fact, in such situations the entrainment of solid particulates in the flowing fluid and deposition on different zones of the flow line yields serious operational challenges and an overall decrease in production efficiency. The loss of productivity leads to a large number of costly remediation work during a well life cycle. In some cases up to $5 Million per year is the estimated cost of removing the blockage plus the production losses during downtimes. Furthermore, some of the oil and gas fields may be left abandoned prematurely, because of the significance of the damage which may cause loss about $100 Million. In this dissertation, we developed a robust wellbore model which is coupled to our in-house developed compositional reservoir model (UTCOMP). The coupled wellbore/reservoir simulator can address flow restrictions in the wellbore as well as the near-wellbore area. This simulator can be a tool not only to diagnose the potential flow assurance problems in the developments of new fields, but also as a tool to study and design an optimum solution for the reservoir development with different types of flow assurance problems. In addition, the predictive capability of this simulator can prescribe a production schedule for the wells that can never survive from flow assurance problems. In our wellbore simulator, different numerical methods such as, semi-implicit, nearly implicit, and fully implicit schemes along with blackoil and Equation-of-State compositional models are considered. The Equation-of-State is used as state relations for updating the properties and the equilibrium calculation among all the phases (oil, gas, wax, asphaltene). To handle the aqueous phase reaction for possible scales formation in the wellbore a geochemical software package (PHREEQC) is coupled to our simulator as well. The governing equations for the wellbore/reservoir model comprise mass conservation of each phase and each component, momentum conservation of liquid, and gas phase, energy conservation of mixture of fluids and fugacity equations between three phases and wax or asphaltene. The governing equations are solved using finite difference discretization methods. Our simulation results show that scale deposition is mostly initiated from the bottom of the wellbore and near-wellbore where it can extend to the upper part of the well, asphaltene deposition can start in the middle of the well and the wax deposition begins in the colder part of the well near the wellhead. In addition, our simulation studies show that asphaltene deposition is significantly affected by CO₂ and the location of deposition is changed to the lower part of the well in the presence of CO₂. Finally, we applied the developed model for the mechanical remediation and prevention procedures and our simulation results reveal that there is a possibility to reduce the asphaltene deposition in the wellbore by adjusting the well operation condition. / text

La compréhension des écoulements à bulles dans les centrales nucléaires demeure encore un élément limitant dans l’analyse des opérations et de la sûreté des installations. Pour ne citer qu’un exemple, l’amélioration de la durée de vie etde la performance des générateurs de vapeur nécessite d’appréhender les régimes d’écoulement au sein des tubes qui sont responsables de leur vibration. Cependant, pour simuler avec précision ces écoulements, les codes de simulation numérique doivent relever de nombreux défis parmi lesquels la capacité à simuler des inclusions ayant des tailles très variées. Dans cette thèse, une nouvelle approche, appelée approche multi-champ, est implémentée dans le code NEPTUNE_CFD, basé sur un modèle bi-fluide. Cette approche inclut une méthode de suivi d’interface pour les grandes structures déformables et prend en compte les effets liés à la turbulence et aux changements de phase.Pour simuler de tels écoulements complexes en limitant le coût CPU, l’approche multi-champ considère séparément les petites inclusions sphériques des grandes inclusions déformables. Ainsi, les petites structures sphériques sont définies via un champ eulérien dispersé évoluant au sein d’un champ continu porteur, comme c’est habituellement le cas avec le modèle bi-fluide. Les grosses bulles déformables sont considérées comme des interfaces entre deux champs continus, un champ liquide et un champ gaz. Si on prend l’exemple d’un écoulement diphasique avec de l’eau et des bulles d’air de différentes tailles, trois champs sont alors définis pour cet écoulement: un champ continu liquide, un champ continu gaz et un champ dispersé gaz contenant les petites bulles sphériques. Cependant, simuler avec précision des interfaces entre deux champscontinus avec le modèle bi-fluide nécessite le développement de traitements spécifiques afin de coupler les deux champs à l’interface et de limiter la diffusion de cette interface.Après avoir amélioré la simulation des interfaces dans des écoulements laminaires, les effets liés à la turbulence sont étudiés. Une étude a priori de simulations aux grandes échelles est proposée pour identifier les termes sous-mailles et comparer différents modèles de turbulence disponibles dans la littérature. L’implémentation et la validation du modèle de turbulence retenu suite à l’étude sont détaillées. Les changements de phase sont ensuite explorés via le développement d’un modèle spécifique pour le terme de transfert de masse. Pour finir, des simulations trois champs sont présentées. De nouveauxcritères sont définis pour modéliser la fragmentation des grandes inclusions déformables en petites bulles sphériques ainsi que la coalescence de ces dernières pour former de grandes bulles déformables.A chaque étape de l’implémentation des différents modèles évoqués, des validations basées sur des données analytiques et issues d’expériences sont présentées afin de s’assurer que les phénomènes physiques sont bien prédits. Des cas tests dans des configurations industrielles sont également détaillés pour montrer la capacité de l’approche développée à simuler des écoulements complexes / Bubbly flows occurring in nuclear power plants remain a major limiting phenomenon for the analysis of operation and safety. As an example, the improvement of steam generator lifetime and performance relies on the comprehension of flow regimes inside the tubes responsible for tube vibrations. However, to ensure an accurate simulation of these flows, theComputational Multi-Fluid Dynamics (CMFD) codes have to take up many challenges, among others the ability of dealing with a variety of inclusion sizes. The classical two-fluid model allows simulating small spherical inclusions but is not able to compute large deformable inclusions. Thus, in this thesis, a new approach, called the multifield approach, is implementedin the CMFD code NEPTUNE_CFD, based on a two-fluid model. This approach includes an interface tracking method for large and deformable structures and takes into account turbulence and phase change effects.To simulate such complex flows with reasonable computational costs, the multifield approach considers separately the small spherical inclusions and the large deformable ones. Thus, the small spherical structures are defined as a dispersed field evolving in a continuous carrier field, as usually done in the two-fluid model. The large deformable bubbles are considered as interfaces between two continuous phases treated as two different fields in the two-fluid model. In the example of a two-phase flow with water and air bubbles of different sizes, three fields are defined: a continuous liquid field, a continuous gas field and a dispersed gas field containing the small spherical bubbles. However, the accurate simulation of interfaces between the two continuous fields within the two-fluid model requires specific treatments to couple the two fields at the interface and to limit the interface smearing.After improving the interface simulation in laminar flows, turbulence effects are investigated. An a priori Large Eddy Simulation (LES) study is performed to identify the predominant subgrid terms and to compare different availableturbulence models. The implementation and validation of the most suitable model is proposed. Phase change interfaces are then explored with the development of a specific model for the mass transfer term. Finally, three fields simulations are performed. New criteria are defined for the breakup of the large deformable inclusions into small spherical bubbles and for the coalescence of the latter forming large deformable bubbles.Validation at each step of the models implementations are presented using analytical and experimental data to ensure that the physical phenomena are well predicted. Test cases in industrial configurations are finally performed to show the ability of the developed approach to deal with complex flows