In this paper experimental and computational modeling methods for studying Multiphase flows in porous and fractured media are studied. Particular attention was given to the flows in a laboratory-scale flow cell model. It is shown that the gas-liquid flows generate fractal interfaces and the viscous and capillary fingering phenomena are discussed. Experimental data concerning the displacement of two immiscible fluids in the lattice-like flow cell are presented. The flow pattern and the residual saturation of the displaced fluid during the displacement are discussed. Numerical simulations results of the experimental flow cell are also presented. The numerical simulation results for single and Multiphase flows through rock fractures are also presented. Fracture geometry studied was obtained from a series of CT scan of an actual fracture. Computational results show that the major losses occur in the regions with smallest apertures. An empirical expression for the fracture friction factor is also described. Applications to CO2 sequestration in underground brine fields depleted oil reservoir stimulation are discussed.    

A preconditioned five-equation two-phase model coupled with an interface sharpening technique is introduced for simulation of a wide range of Multiphase flows with both high and low Mach regimes. Harten-Lax-van Leer-Contact (HLLC) Riemann solver is implemented for solving the discretized equations while tangent of hyperbola for interface capturing (THINC) interface sharpening method is applied to reduce the excessive diffusion of the method at the interface. In this work, preconditioning technique is used in a system of equations including viscous and capillary effects. Several one-and two-dimensional test cases are used to evaluate the performance and accuracy of this method. Numerical results demonstrate the efficiency of preconditioning in low Mach number flows. Comparisons between results of preconditioned and conventional system highlight the necessity of using preconditioning technique to reproduce main characteristics of low-speed flow regimes. Additionally, preconditioned systems transform to the conventional systems at high Mach number flows thus exhibiting the same level of accuracy as the standard flow solver. Therefore, the preconditioned compressible two-phase method can be used as an all-speed two-phase flow solver accounting for capillary and viscous stresses.

In this paper, the Multiphase lattice Boltzmann collision models are evaluated by a comparative study for the simulation of liquid-vapor two-phase flow problems. Herein, the single-relaxation-time (SRT) scheme based on the Bhatnagar-Gross-Krook (BGK) approximation and the multiple-relaxation-time (MRT) method with two different forcing schemes are considered. The pseudo-potential Shan-Chen (SC) model is used to resolve the inter-particle interactions between the liquid and gas phases. In the standard form of the SC model, the interaction force is imposed in the momentum field which unphysically causes the density ratio to change with the variation of relaxation time. In this study, a modified form of this model is implemented to decouple these two physical parameters. Herein, the interaction force is imposed using the exact difference method (EDM). The efficiency and accuracy of the present numerical scheme based on the lattice Boltzmann method (LBM) with the SRT and MRT schemes are examined for simulation of two-phase flows in different conditions. The equilibrium state of a droplet in the periodic flow domain and on the flat surface with hydrophobic and hydrophilic wetting condition are computed to investigate the robustness and performance of the collision operators applied. The results obtained for these problems are compared with the analytical solutions which shows a good agreement. The collision of a droplet on the liquid film at various flow conditions is investigated and the predicted results are presented at a range of the Weber and Reynolds numbers. The present study demonstrates that the SRT model suffers from the spurious velocity in the interfacial region which causes numerical instabilities at moderate Reynolds and Weber numbers. It is found that the MRT model is stable for all the cases considered in the present work even at high Reynolds and Weber numbers. In terms of the computational efficiency, the SRT scheme is slightly attractive, although the computational cost of this model is not considerably lower than MRT scheme. The present study suggests the lattice Boltzmann method with the MRT collision operator incorporated with the EDM technique is robust, sufficiently accurate and computationally efficient to resolve the practical liquid-vapor two-phase flow structures and properties.

In this work, the accuracy of the Multiphase lattice Boltzmann method (LBM) based on the phase-field models, namely the Cahn-Hilliard (C-H) and Allen-Cahn (A-C) equations, are evaluated for simulation of two-phase flow systems with high-density ratios. The mathematical formulation and the schemes used for discretization of the derivatives in the C-H LBM and A-C LBM are presented in a similar notation that makes it easy to implement and compare these two phase-field models. The capability and performance of the C-H LBM and A-C LBM are investigated, specifically at the interface region between the phases, for simulation of flow problems in the two-dimensional (2D) and three-dimensional (3D) frameworks. Herein, the equilibrium state of a droplet and the practical two-phase flow problem of the rising bubble are considered to evaluate the mass conservation capability of the phase-filed models employed at different flow conditions and the obtained results are compared with available numerical and experimental data. The effect of employing different equations proposed in the literature for calculating the relaxation time on the accuracy of the implemented phase-field LBMs in the interfacial region is also studied. The present study shows that the LBM based on the A-C equation (A-C LBM) is advantageous over that based on the C-H equation in dealing with the conservation of the total mass of a two-phase flow system. Also, the results obtained by the A-C LBM is more accurate than those obtained using the C-H LBM in comparison with other numerical results and experimental observations. The present study suggests the A-C LBM as a sufficiently accurate and computationally efficient phase-field model for the simulation of practical two-phase flows to resolve their structures and properties even at high-density ratios.

Fluidized beds are conventional components of many industrial processes, such as coal gasification for energy generation and syngas production. Numerical simulations help to properly design and understand the complex Multiphase flows occurring in these reactors. Two modeling approaches are usually adopted to simulate Multiphase flows: the two fluids Eulerian-Eulerian model and the continuous/discrete Eulerian-Lagrangian model. Since fluidized beds account for an extremely large number of particles, tracking each of them could not assure to get results within a reasonable computational time. The Computational Particle-Fluid Dynamics (CPFD) approach, which belongs to the Eulerian-Lagrangian models class, groups together particles with similar key parameters (e. g. composition, size) into computational units (parcels). Parcel collisions are modeled by an isotropic solid stress function, depending on solid volume fraction. In this paper, the bubbling fluidized bed (BFB) upstream gasifier of the EU research infrastructure ZECOMIX (Zero Emissions of Carbon with Mixed technologies) has been simulated using a CPFD approach via Barracuda® software. The effect of different fluidizing agent injection strategies on bed bubbling and mixing, for non-reacting cases, has been studied. The numerical results for a reacting case have been compared to the available experimental data, gathered during the coal gasification campaign. The model has proved to be very useful in the choice of the more efficient injection configuration that assures a more effective contact of the gas with the solid bed and a good bubbling fluidization regime, together with a satisfactory prediction of the outlet gas composition. The numerical approach has turned out to be robust and time-saving and allowed to dramatically reduce the computational cost with respect the classical two fluids Eulerian-Eulerian models.

Cavitating flow through the nozzle is numerically simulated by using the Multiphase lattice Boltzmann method. The pseudo-potential Shan-Chen model is used to resolve inter-particle interactions, modeling phase change between the liquid and vapor phases and imposing the surface tension at the interface. The numerical algorithm implemented is simple for programming and efficient for simulation of Multiphase cavitating flows comparing to the traditional Navier-Stokes solvers with complicated cavitation models. Efficiency and accuracy of the Multiphase lattice Boltzmann method with Shan-Chen model for simulation of cavitating flows through the nozzle are examined by computing the cavitation inception, growth and collapse and the results obtained are compared with the existing numerical results in the literature. The study shows that the present computational technique is robust and efficient to predict the cavitation phenomena in the geometries studied.

Natural debris floods travel in straight and meandering courses. The flow behaviour greatly depends on the volume fractions of solid and fluid, as well as on their dynamic interactions with the channel geometry. For the quasi three-dimensional simulations of flow dynamics and mass transport of these floods through meandering and straight channels, we employ a two-phase debris flow model to carry out simulations for debris floods within straight and sine-generated meandering channels of different amplitudes. The results for different sinuous meandering paths are compared with that in the straight one in terms of phase velocity, downslope advection and dispersion, depths of the maxima, deposition of mass, position of front and rear parts of the solid and fluid phases, and also the flow dynamics out of the conduits. The results reveal the slowing of the flow and increase of momentary deposition of the mixture mass in the vicinity of the bends along with the increasing sinuosity. The numerical experiments are useful to better understand the dynamics of debris floods down meandering channels as seen in the natural paths of the rivers as well as already existing channels like episodic rivers in hilly regions. The results can be extended to propose some appropriate mitigation strategies.

A Multiphase flow meter is designed to measure the flow rate of two or more phases without phaseseparation. The flow meter must be accurate enough for the desired application. It must be capable to measure the specifications throughout phase fraction of each phase, independent of the flow regime. Various factors are effective on selection of the flowmeter. Moreover, various procedures are present for measurement of multi-phase flows. In this study, a comprehensive review has been implemented on various technologies in multi-phase flowmeasurement in oil industry and the basis of various measurement techniques has been investigated. The advantages, requirements, and constraints of each technology have been reviewed. Finally, the recent advances in this field have been provided for the researchers.

The multiscale Multiphase flow contains both small-scale (dispersed phase) and large-scale (continuous phase) structures. Standard interface-averaging Multiphase models are appropriate for the simulation of flows including small-scale structures. Standard interface-resolving Multiphase models are commonly used for the simulation of flow regimes containing large-scale structures. The accurate simulation of different regimes has a crucial role to investigate the physics of Multiphase flows. To cover the inability of standard models to simulate multiscale Multiphase flows, various generalized hybrid models have been developed. The present research aims to present an LES-like approach to identify the large-scale structures by comparing the equivalent diameter of structures and the averaging length scale. The main difference between the presented model and the models available in the literature is the independency of the model to the thresholds of the local volume fraction to recognize the flow regime. The switching criterion is set based on the cell size and the physical phenomena including the break-up and coalescence mechanisms. To assess the capabilities of the presented multiscale model, four different benchmark cases including the bubble column, the impinging jet, the dam break, and the Rayleigh-Taylor instability are investigated. The physical behavior of the flow is considered as a reference and compared with numerical results. It is demonstrated that the present multifluid model is capable to capture the physical characteristics of both dispersed and segregated flow regimes, and it is a forward step to develop a generalized multiscale hybrid Multiphase model.