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Prevalent uncertainties in multi-phase modeling are investigated. Toward this, the critical role of interface capturing strategy is demonstrated for realistic flow determination. Numerical modeling of the plume is discussed through the impact of various forces and uncertainties associated with them. Finally, results from different turbulence modeling approaches are compared to ascertain the adequacy of Reynolds averaged modeling vis-à-vis large eddy simulation within the domain of eddy viscosity-based modeling. [ABSTRACT FROM AUTHOR]

Jet impingement serves as an effective method to enhance heat transfer in diverse industrial applications, utilizing either a separate fluid from the ambient (free-surface jet) or identical fluids (submerged jet). The target surface undergoes distinct thermal processes, featuring zones like the stagnation zone, boundary layer formation, and the transition from laminar to turbulent wall flow. However, heat transfer efficiency diminishes significantly due to pressure gradient changes beyond the stagnation zone, impeding flow and boundary layer development. Addressing this decline through surface modification techniques, such as incorporating spherical dimples, emerges as an innovative approach. This study develops a numerical model via Computational Fluid Dynamics (CFD) simulations utilizing Volume of Fluid (VOF) modeling for water jet impingement on a flat plate target. The model's validity is established by comparing hydrodynamic and thermal aspects in both laminar and turbulent scenarios against established experimental data in literature. Nine dimpled target surfaces, featuring diverse dimensional properties and positioning configurations, are examined using this model to explore potential enhancements in heat transfer intensity. The findings indicate a notable increase in the overall surface average Nusselt number, potentially reaching up to 50% by implementing dimples in the current context. Moreover, the study highlights that the radial distribution of dimples and the non-uniform flow path ahead of the incoming fluid, which differs from parallel flat flow, result in varying effects based on dimensional properties. For instance, it has been found that modifying dimensions such as deepening dimples or altering their proximity could yield contrary effects, emphasizing the need for an optimization methodology to determine the most efficient dimpled surface setup within a given geometry. [ABSTRACT FROM AUTHOR]

Electron beam melting is a powder bed fusion process capable of manufacturing parts from a variety of high-temperature alloys. Given that the process relies on feedstock recycling for process economics, understanding process-part quality relationships is critical. This work investigates process-part quality relationships in terms of the internal and external defects and component microstructure relative to a feedstock subjected to 33 build cycles without replacement. To accomplish this, a volume of fluid mesoscale model consisting of three different powder distributions were considered: (1) Monomodal; (2) As-measured; and (3) Irregular. Particle morphology was characterized using shape factors examined via optical microscopy. To approximate the particle shapes in three-dimensions, a method is presented that utilizes a binarized domain to define low frequency, macroscale particle "base" shapes implicitly and is thus not restricted to starlike particles. The discrete element method was also used to investigate velocity distributions and packing densities of the as-measured and irregular particles with respect to deviations in the nominal layer thickness of 50 μm. In general, beam power and scan speed were found to have an appreciable effect on microstructure formation and surface roughness. Finally, correlations were found between specific classifications of irregular particles and lack of fusion defect formation. [ABSTRACT FROM AUTHOR]

We compared the accuracy of volume of fluid (VOF) methods in unstructured solvers using the following five different methods: 1 - the algebraically compressive VOF method, 2 – simple coupled VOF method with Level Set (S-CLSVOF) method, 3 - interface-compressing VOF method incorporated with Laplacian filter (VOFL), 4 - isoAdvector method, and 5 - isoAdvector method incorporated with Laplacian filter (isoAdvectorL) by incorporating them into OpenFOAM®, an open-source software. To evaluate these methods under proper conditions, we compared the calculation accuracy using the optimized parameters, which are explored by Bayesian optimization. The test cases for advection accuracy of volume fraction and for imbalance of surface tension force in static multiphase fluid fields were considered. In this study, we found that the compression parameters and maximum Courant number should be adjusted to obtain high accuracy simulation according to the simulation condition in VOF and S-CLSVOF method. In VOFL and isoAdvectorL methods, the spurious current can be extremely reduced, which means that these methods are suitable for slow flow with higher Laplace number conditions. [ABSTRACT FROM AUTHOR]

Both straight and curved carbon fibers are widely used in various commercial gas diffusion layer (GDL) fabrications. The effect of the different carbon fiber curvatures on two-phase flow dynamics within the cathode GDLs of proton exchange membrane fuel cells remains unclear. In this study, we investigate liquid transport in three types of GDLs with varying fiber curvatures using the two-phase volume of fluid simulations in OpenFOAM. For the first time, a rod periodic surface model is combined with a layer-by-layer fiber stacking strategy, to stochastically reconstruct GDL structures while incorporating crucial parameters from physical (experimental) GDLs. A grid independence study and model validation are conducted. Following pore network analysis of pore size distribution and connectivity, we study the time-varying GDL total and local water saturation and capillary pressure. Despite maintaining similar layer and bulk porosity, increased fiber curvature enhances pore connectivity but raises water saturation and capillary pressure, increasing the risk of flooding. Additionally, droplets in gas channels with straight-fiber GDLs are larger and have slower movement than those in curved-fiber GDLs. Fiber curvature inversely affects drainage capacity in GDLs and connected channels. With comparable water saturation and capillary pressure, curved-fiber GDLs exhibit lower discrepancies, suggesting improved uniformity in water distribution. [Display omitted] • Curved and straight fiber GDLs are reconstructed with similar bulk and layer porosity. • Increasing fiber curvature enhances pore connectivity and pore quantity. • GDL water saturation and capillary pressure increase with an increased fiber curvature. • Increasing the amount of small pores results in stronger water spreading within GDLs. • Detached droplets in GCs have smaller sizes and longer liquid bridge when using curved-fiber GDLs. [ABSTRACT FROM AUTHOR]

Understanding the counter-flow of liquid inlet and gas outlet at the interface between the electrolyte and cathode gas diffusion layer (GDL) is crucial for water management in proton exchange membrane fuel cells. Existing studies typically overlook air outlets and assume a fixed liquid inlet direction. This study uses a volume of fluid method to model two-phase interactions in a T-shaped GDL and gas channel (GC) assembly, with GDL geometry derived from nano-computer tomography. Considering potential electrode deformations, such as local cracks and blockages, this research investigates the impact of the size and shape of liquid invasion on the liquid-gas behavior in the cathode GDL and GC using five liquid injection configurations. Simulations also incorporate GDL gas outlets, integrating them with a tailored liquid inlet setup. Results show that the injection site and configuration significantly affect water behavior in the GDL, affecting saturation, stabilization, and breakthrough, followed by drainage in the GCs. Comparisons of simulations with and without air outflow show distinct counter-flow interactions, highlighting variations in water distribution and discrepancies in two-phase transport across the GCs. [ABSTRACT FROM AUTHOR]

This study investigates the characteristics of submerged vortices in an intake sump through a combination of numerical simulations, experimental validations, and advanced modeling techniques. The aim of this study is to gain insights into the complex flow patterns and vortex structures within the sump, focusing on their behavior under varying flow rates. The Shear Stress Transfer (SST) k-ω model is utilized to capture turbulence, and the Volume of Fluid (VOF) method is employed to visualize the water-air interface. Model tests are conducted to validate the simulations. The findings suggest that under low flow conditions, the flow beneath the bell mouth becomes highly turbulent, leading to the formation of a complex vortex system with three distinct high-pressure zones. With increasing flow rates, the shape and strength of these high-pressure zones fluctuate, and a quadrupole vortex structure emerges at the sump bottom. This quadrupole vortex plays a pivotal role in the transformation of a floor-attached vortex upward, culminating in a dual vortex column structure. This structure, in turn, generates additional low-amplitude pressure pulsations. Wall-attached vortices are also observed on both sides of the inlet pipe, a result of flow stratification due to velocity disparities. The insights gained from this study contribute to a deeper understanding of intake sump dynamics and offer valuable guidance for designing and optimizing fluid systems to mitigate potential turbulence-related issues. [ABSTRACT FROM AUTHOR]

This study investigates the characteristics of submerged vortices in an intake sump through a combination of numerical simulations, experimental validations, and advanced modeling techniques. The aim of this study is to gain insights into the complex flow patterns and vortex structures within the sump, focusing on their behavior under varying flow rates. The Shear Stress Transfer (SST) k-ω model is utilized to capture turbulence, and the Volume of Fluid (VOF) method is employed to visualize the water-air interface. Model tests are conducted to validate the simulations. The findings suggest that under low flow conditions, the flow beneath the bell mouth becomes highly turbulent, leading to the formation of a complex vortex system with three distinct high-pressure zones. With increasing flow rates, the shape and strength of these high-pressure zones fluctuate, and a quadrupole vortex structure emerges at the sump bottom. This quadrupole vortex plays a pivotal role in the transformation of a floor-attached vortex upward, culminating in a dual vortex column structure. This structure, in turn, generates additional low-amplitude pressure pulsations. Wall-attached vortices are also observed on both sides of the inlet pipe, a result of flow stratification due to velocity disparities. The insights gained from this study contribute to a deeper understanding of intake sump dynamics and offer valuable guidance for designing and optimizing fluid systems to mitigate potential turbulence-related issues.

Interface tracking simulations of gas–liquid Taylor flow in horizontal square microchannels were carried out to understand the relation between the pressure drop in the bubble part and the curvatures at the nose and tail of a bubble. Numerical conditions ranged for 0.00159 ≤ CaT ≤ 0.0989, 0.0817 ≤ WeT ≤ 25.4, and 8.33 ≤ ReT ≤ 791, where CaT, WeT, and ReT are the capillary, Weber, and Reynolds numbers based on the total volumetric flux. The dimensionless pressure drop in the bubble part increased with increasing the capillary number and the Weber number. The curvature at the nose of a bubble increased and that at the tail of a bubble decreased as the capillary number increased. The variation of the curvature at the tail of a bubble was more remarkable than that at the nose of a bubble due to the increase in the Weber number, which was the main cause of large pressure drop in the bubble part at the same capillary number. The relation between the bubble velocity and the total volumetric flux was also discussed. The distribution parameter of the drift-flux model without inertial effects showed a simple relation with the capillary number. A correlation of the distribution parameter, which is expressed in terms of the capillary number and the Weber number, was developed and was confirmed to give good predictions of the bubble velocity. [ABSTRACT FROM AUTHOR]

A novel volume of fluid method is presented for mineral precipitation coupled with fluid flow and reactive transport. The approach describes the fluid-solid interface as a smooth transitional region, which is designed to provide the same precipitation rate and viscous drag force as a sharp interface. Specifically, the governing equation of mineral precipitation is discretized by an upwind scheme, and a rigorous effective viscosity model is derived around the interface. The model is validated against analytical solutions for mineral precipitation in channel and ring-shaped structures. It also compares well with interface tracking simulations of advection-diffusion-reaction problems. The methodology is finally employed to model mineral precipitation in fracture networks, which is challenging due to the low porosity and complex geometry. Compared to other approaches, the proposed model has a concise algorithm and contains no free parameters. In the modeling, only the pore space requires meshing, which improves the computational efficiency especially for low-porosity media. [ABSTRACT FROM AUTHOR]

Using loop heat pipes (LHPs) for thermal management of aerospace and ground electronic devices has become an efficient and attractive method in recent years. A 3-D CFD numerical model was proposed for calculating the thermo-hydraulic behavior in a LHP with a square evaporator and the accuracy was verified by experimental results. The evaporation and condensation were addressed by volume of fluid method and a momentum source term derived from flow resistance analysis was incorporated into wick as the capillary force. The simulation results aligned with experimental trends, and errors of heating surface temperature and system thermal resistance were small. Due to structural constraint and gravity effect, two eddies were formed in compensation chamber, causing uneven distribution of temperature on heating surface. Parametric analysis indicated that higher porosity deteriorated the heat transfer from heating surface to wick and enlarged heating surface temperature and system thermal resistance. Higher wick and shell thermal conductivities ensured more heat conduction to the vapor-liquid interface and enhanced the evaporation intensity. However, the higher the thermal conductivity, the lower the improvement that could be obtained. Additionally, lower heat sink temperature and higher condenser heat transfer coefficient both intensified the LHP working performance by elevating the condensation efficiency.

The Volume of Fluid (VoF) method stands out as a widely utilized tool for capturing interfaces in the numerical simulation of multimaterial fluid flow. Numerous efforts have been invested in enhancing its accuracy and efficiency, including the development of analytic reconstruction methods. Despite these advancements, there exists a continued need for further improvements in the accuracy, efficiency, and robustness of the VoF method in practical applications. In the conventional VoF method, information from neighboring cells is crucial for computing the normal vector of the interface in each multimaterial cell, requiring data from as many as 26 neighboring cells in 3D VoF methods. This paper introduces a novel VoF method named SVoF, which departs from traditional approaches by eliminating the necessity for information from neighboring cells. In the SVoF method, the data provided for interface reconstruction in each multimaterial cell consists of the volume fractions of fluids in several subcells within the cell itself. Initially, these data are determined by the initial conditions. In MMALE methods, these data can be updated through a closure model for multimaterial cells in each Lagrangian stage and remapped in each subsequent remapping stage. The determination of the normal vector of the linear interface in SVoF is achieved through an optimization procedure. The objective function of this procedure is the sum of the squares of the differences between the given volume fractions and the reconstructed volume fractions of the reference fluid in specific subcells. The optimization procedure is solved using an improved quadratic fit golden section algorithm. Similar to traditional VoF methods, the intercept of the linear interface is calculated by precisely matching the given volume fraction of the reference fluid throughout the entire multimaterial cell. The SVoF method is characterized by its ease of coding and implementation, making it suitable for interface reconstruction in multimaterial cells containing three materials. Building upon the SVoF method, a new cell-centered MMALE method is developed, showcasing robustness. This new MMALE method utilizes Tipton's pressure relaxation model for the closure of multimaterial cells and leverages the SVoF method for interface reconstruction. Numerical results demonstrate that the SVoF method can precisely reproduce linear interfaces, approaching second-order accuracy, and that this new MMALE method exhibits significant robustness. • A novel VoF method (SVoF) that doesn't require information from neighboring cells. • SVoF requires the volume fractions of fluids in multiple subcells within each multimaterial cell. • SVoF is applicable for interface reconstruction in multimaterial cells containing three distinct materials. • SVoF precisely reproduces linear interfaces and is straightforward to code and implement. • MMALE combined with SVoF demonstrates greater robustness compared to the existing MMALE coupled with MoF. [ABSTRACT FROM AUTHOR]

Drying is a critical process step during battery electrode production due to its microstructure defining nature. Distribution and interconnectivity of active material particles, pores, and the overall porosity significantly influence the later cell performance. Knowledge about structure formation as well as electrode property prediction are crucial for optimization and targeted electrode design. However, the exact microprocesses during electrode drying are not yet understood well and very difficult to access experimentally. Therefore, in this study, a combination of computational fluid dynamics (CFD) and discrete element method (DEM) simulation models for investigating structure formation considering particle–particle as well as fluid‐particle interactions and vice versa is presented. , The volume of fluid method is used for taking into account the fluid‐fluid interface, evaporation and capillary interactions. The simulations reveal the formation of a top–down consolidation front which interacts with the fluid leading to a backflow of liquid. The results show good agreement with experimental measurements for NMC622 cathodes. Furthermore, the influence of production parameters such as mass loading and solids content is examined. The findings demonstrate the modeling tool's suitability for process engineers to anticipate and enhance electrode characteristics and facilitate scientists to understand complex structure formation relationships. [ABSTRACT FROM AUTHOR]

A piecewise circular interface construction (PCIC) method is described, where height functions based curvature estimates are directly utilised for accurate interface reconstruction under the framework of volume of fluid method. The present work is an attempt to develop a robust and accurate higher order interface reconstruction algorithm that is capable of accurate simulation of surface tension dominated flows. The proposed hybrid method (H‐PCIC) is thus able to take advantage of merits of both PCIC and HF methods, achieving at least second order convergence with respect to both interface reconstruction and curvature computation. This is in addition to the significantly superior quality of the reconstructed interface with respect to PLIC methods. This seamless blending of the HF and PCIC quantities is enabled by c0‐correction procedures applied to base PLIC and initial PCIC steps. More recent variants of the height function method with variable stencil size are used for calculation of radius of curvature. The capability of this proposed method towards simulation of flow problems within a well‐balanced two‐phase solver is established with help of multiple complex two‐phase flow problems. This validation exercise also demonstrates the capability of PCIC class of methods towards solutions of two‐phase flows with intricate physics. [ABSTRACT FROM AUTHOR]

Dams hinder water circulation and consequently disrupt the river continuum which adversely affects aquatic organisms and degrades water quality. An alternative new concept for a dam has been proposed with an optimal design that prevents seawater from flowing upstream while maintaining the continuity of the river–estuary ecosystem. A Tesla valve was used because its asymmetric geometry increases the flow resistance only in a single direction. The numerical model setup aimed to simulate wave-induced open-channel flows in OpenFOAM using the volume of fluid method and investigate the capability of the channel design to enhance the asymmetric flow resistance, and the model was validated by laboratory experiments. Various combinations, scales, shapes, and arrangements of the structures were considered for deployment. Subsequently, these designs were evaluated based on the difference in flow discharges in each flow direction. The optimal choice included a 30° angle between the sidewalls and the structures, and streamwise spacing between the structures at 5/3 times the channel width. Further, longer main structures with substructures and a slightly offset design can help increase the flow asymmetry in bidirectional open-channel flows. Although the present study has limitations in terms of methodology and complex structural factors, the proposed design suggests the basic design of a new concept for Tesla valve-like geometry. [ABSTRACT FROM AUTHOR]

In a laterally excited, partially liquid-filled U-shaped container, oscillation is the predominant motion of the liquid. However, there would be some sloshing in the liquid free surface at the vertical limbs of the container. Due to the presence of high-energy velocity pulses, near-fault ground motions can cause significant sloshing in the vertical limbs of the container. Thus, it is necessary to examine the effect of near-fault earthquake excitations on the sloshing liquid height, sloshing-induced hydrodynamic pressure, and shear stress at the walls of the U-shaped containers. The same is attempted in this paper. The standard "k-epsilon" turbulence model with enhanced wall function is considered in this study. The outcome of this study reveals that the time-wise frequency variation of the near-fault ground motions significantly affects the sloshing response of the liquid stored in the U-shaped containers. It is observed that the sloshing-induced hydrodynamic pressure is severely influenced by the frequency content of the ground motion records rather than their peak ground acceleration. [ABSTRACT FROM AUTHOR]

Droplet impact on a substrate is an intriguing phenomenon that widely exists in our daily life and a broad range of industrial processes. However, droplet impact dynamics on soft textured surfaces are less explored and the underlying mechanisms remain elusive. Here, we report numerical simulation of droplet impact dynamics on a micropillar-arrayed soft surface using BASILISK, which involves a multiscale geometric domain containing the micropillars and droplet that are in the order of µm and mm, respectively. As such, the volume of fluid (VOF) method is coupled with the finite volume method (FVM) to build the fluid fields and track their interface. From a conceptual point of view, the micropillared substrate is formed by imposing interstitial gaps into the otherwise intact soft material, whose viscoelastic properties can be quantified by gap density ϵ. Via a five-parameter generalized Maxwell model, the viscoelastic properties of the micropillared substrate can be approximated by its equivalent elastic response in the Laplace--Carson (LC) space, and the averaged bulk strain of the micropillared substrate in the real space is obtained by the inverse LC transform. Moreover, through parametric studies of splash extent, it turns out that for a specific ϵ, the splash is dramatically intensified with increasing impact velocity Ui. The splash also turns more violent with increasing ambient pressure Pa, which is evidenced by a larger splash angle of 114.44° between the ejected sheet and the horizontal substrate at 5 atm. Conversely, the splash becomes more depressed with increasing surface tension σ. Overall, the splash magnitudes of our simulations agree well with those predicted by the Kelvin-Helmholtz instability theory. By leveraging the LC transform in the fluid-viscoelastic solid interactions, our simulation methodology captures the main features of droplet impact dynamics on microstructured viscoelastic surfaces by means of the mechanically averaged responses while avoiding the predicament of domain scale inconsistency. [ABSTRACT FROM AUTHOR]

Recently, there has been renewed interest in hollow droplets impaction since its great significance for thermal spraying, the three-dimensional (3D) printing of foam material. In the present study, we numerically study the dynamic characteristics of a hollow droplet obliquely impacting the liquid film via the volume of fluid (VOF) method. The splash formation and evolution during the oblique hollow droplet impact process under different conditions are investigated. The impact angle, film thickness, and impact velocity influences are analyzed. The results demonstrate that, with the impact angle increasing, the variation trends of the crown radius on both sides are opposite. When the film thickness increases, there is a critical film thickness at which the right crown height reaches the maximum. The increasing impact velocity leads to a flow phenomenon transition from non-splashing to splashing and even to a crown. When the impact velocity reaches a certain value, the liquid film on the front side will become unsteady, which makes the crown on this side prone to rupture at the early stage of impact. The bubble deformation during the impact process under different conditions is also discussed, and the patterns of the splashing behaviour under different initial conditions are summarized. [ABSTRACT FROM AUTHOR]

Here we present a 2D planar simulation of the collisions between liquid droplets and solid particles that are most often used in industrial applications. The collisions are modeled using a combination of Volume of Fluid and Level Set methods. We study the impact of the particle-to-droplet size ratio and the shape of solid particles on the collision behavior and interaction regimes. The findings are presented in the form of collision regime maps. The interaction regimes are also distinguished for binary droplet collisions: deposition, separation, and disintegration. We show the impact of density, viscosity, and surface tension on the droplet collision regime maps as well as on the number of secondary fragments. The practical value of the research comes from the newly established differences of collision regimes between droplets and particles of different shapes and sizes.

In this study, an efficient conversion algorithm of level set function [Formula: see text] from volume fraction [Formula: see text] is developed. This method makes the calculation of [Formula: see text] easier than the conventional CLSVOF method, and the precision of surface tension can be improved by the application of [Formula: see text] The two numerical tests are shown to demonstrate the proposed scheme. As a result of two demonstration tests, it is obtained that (a) the proposed method gives better [Formula: see text] than that of the existing simple coupled method because this can take into account multi-dimensional profiles of [Formula: see text] (b) a surface tension evaluated by using the proposed method can contribute to much lower spurious currents, (c) the proposed method can simulate bubble generation with a similar precision of rigorous CLSVOF method.

Increasing the efficiency of hydrocarbon field development is an important issue. One of the methods for increasing oil recovery is the injection of aqueous solutions of polymers. Although this method has been known and used for quite some time, further systematic research is needed to further improve its effectiveness. In this work, systematic computational studies of the features of oil displacement by aqueous polymer solutions from a naturally fractured structure were carried out. Direct numerical modeling of a two-phase immiscible flow in the process of displacing oil from a natural fracture structure using solutions of anionic polymers based on polyacrylamide was carried out. Aqueous solutions of three different polymers were considered, the concentrations of which varied from 0 to 0.1%, and the molecular weights were from 10 to 20 mln c.u. The rheological properties of polymers and their wetting characteristics have been previously studied in laboratory experiments. A distinctive feature of the polymers considered was the non-Newtonian nature of their aqueous solutions even at low concentrations. To take these processes into account, the computational technique has been extended to the case of non-Newtonian rheology for immiscible two-phase flow in one of the media. During numerical simulations, the effect of the concentration of polymers, their molecular weight, and charging density on the flow regimes in a fractured reservoir have been investigated systematically at various crude oil viscosities. It has been shown that the use of a 0.1% aqueous solution of polyacrymalide can increase the oil-recovery factor by 1.8 times. It has been established that, with an increase in the molecular weight and surface charge density of the polymer, the efficiency of its use for enhancing oil recovery increases. With an increase in the viscosity of the displaced oil, the effect of using the injection of the considered polymers also increases. The data obtained in this work can be used to further improve polymer-flooding technologies for oil fields. [ABSTRACT FROM AUTHOR]

In order to quantitatively analyze the data measurement accuracy of ocean buoys under normal and extreme sea conditions, in this study, we simulated the six-degree-of-freedom motion response of self-designed ocean buoys under different sea conditions based on a separated vortex simulation and the fluid volume method and analyzed the impact of the unsteady motion of buoys on data measurement. The results indicate that under normal sea conditions, the deviation between the numerical method used in this paper and the experimental results is less than 10%. The heaving motion of a buoy is most sensitive to changes in wave conditions. The fluctuation intensity of buoy motion is modulated by the height and wavelength of waves. When the wave height and wavelength are similar to the overall geometric size of a buoy, the wave characteristics of the buoy's heave, yaw, and pitch motion are significant. In addition, under extreme sea conditions, the movement of the buoy can also cause a deviation in the measured velocity in the transverse flow direction, but the overall deviation is less than 10%. In extreme sea conditions, the wind speed measurement results should be corrected to improve the measurement accuracy of a buoy. [ABSTRACT FROM AUTHOR]

The authors have presented results of mathematical modeling of collisions of inhomogeneous droplets of liquids (nonmixed two-fluid droplets and emulsions) in a gas medium between each other. A study was made of the influence of a set of factors on the conditions and integral characteristics of disintegration: of the temperature of the external medium, the concentration of the steam, and the Weber number. The obtained results have shown a satisfactory correlation with experimental results. It has been established that the ratio of the areas of the evaporation surface after and before the interaction as a result of the collisions of inhomogeneous droplets corresponds to the range 0.8–2. It is the central collision of droplets that is the most efficient. Critical values of the Weber number were established above which the ratio of the areas of evaporation surfaces of the droplets after and before the interaction S1/S0 remains constant, in practice. [ABSTRACT FROM AUTHOR]

The present investigations aim to improve the gas-liquid two-phase transport in centrifugal pumps using a novel front shroud design with macroscopic grooves. This increases the secondary flow strength and the two-phase mixing, boosting the performance. A total of 23 different circumferential and radial groove profiles were numerically investigated to identify the best configuration leading to the highest mixing efficiency. Three different loads were considered, i.e., part load, optimal point, and overload. Additionally, the performance of the novel designs was compared with that of the established alternatives, involving two different clearance gaps and/or an inducer. While circumferential grooves already lead to a slightly improved specific delivery work, radial grooves improve noticeably the pump efficiency and deliver a very high two-phase mixing compared to other traditional pump configurations. Under conditions of optimal loading, the utilization of circumferential grooves led to a phase mixing enhancement of approximately 19.5%, whereas the implementation of radial grooves exhibited a notable improvement in mixing efficiency by 64.8% compared to the standard gap. The radial design R14 is superior to all other designs regarding efficiency and phase mixing. It is therefore recommended for transporting gas-liquid two-phase flows. [Display omitted] • Two-phase flows were studied numerically in a centrifugal pump. • A novel front shroud with macroscopic grooves was used to improve the performance. • Circumferential and radial groove profiles were investigated and compared. • Part load, optimal point, and overload flow conditions were considered. • The radial design R14 is always superior regarding efficiency and phase mixing. [ABSTRACT FROM AUTHOR]

Interactions between inclusion particles and the steel–slag interface directly affect the inclusion removal efficiency and thus influence steel cleanliness. Herein, the three‐phase interactions are resolved using the volume of fluid (VOF) method coupled with a dynamic overset mesh. The simulation is able to capture the instantaneous interface deformation and predict the particle motion driven by capillary force. The model validity is first demonstrated by comparison with analytical results. Then, a parameter study is conducted to examine the most influential factors governing the separation process. The results show that the system's wetting condition and the slag viscosity have a decisive effect on particle behavior at the interface (separation or entrapment). From an energy perspective, a better wetting condition generates more energy sources, and the interfacial energy is efficiently transformed into the particle's kinetic energy within a less viscous environment, thus leading to better separation. Besides, a criterion for predicting particle behavior is developed based on a modified Reynolds number (Reγ, relevant to fluid properties) and a quantity related to particle dynamics (ζ). The current work brings insights into the interfacial phenomenon during inclusion removal, which can be incorporated into large‐scale simulations to estimate the removal efficiency more accurately. [ABSTRACT FROM AUTHOR]

Here we present a 2D planar simulation of the collisions between liquid droplets and solid particles that are most often used in industrial applications. The collisions are modeled using a combination of Volume of Fluid and Level Set methods. We study the impact of the particle-to-droplet size ratio and the shape of solid particles on the collision behavior and interaction regimes. The findings are presented in the form of collision regime maps. The interaction regimes are also distinguished for binary droplet collisions: deposition, separation, and disintegration. We show the impact of density, viscosity, and surface tension on the droplet collision regime maps as well as on the number of secondary fragments. The practical value of the research comes from the newly established differences of collision regimes between droplets and particles of different shapes and sizes. [ABSTRACT FROM AUTHOR]

This study is dedicated to comparison of the results of two-dimensional (2D) and three-dimensional (3D) numerical modeling of dynamics of a single bubble rising in stagnant viscous liquid. The volume of fluid method is used to track the moving interface. This method makes it possible to take into account all the forces acting on the interface in a natural way without using empirical data. The solution of the continuity equation, Navier–Stokes equation, and equation for determining the position of interface is based on the finite volume method. When carrying out numerical experiments, the bubble diameter at the initial time is fixed. It is shown that the shape of the bubbles in the vertical section of the computational domain is different in the case of 2D and 3D simulations. It has been established that the rising velocity of bubble in 3D simulation is greater than in 2D simulation. [ABSTRACT FROM AUTHOR]

In a reactor severe accident, molten jet breakup and solidification are important behaviors after large pours of molten material fall into the coolant in-vessel or ex-vessel. However, heat and mass transfer processes inside melt during jet breakup have not been studied sufficiently. Existing research on jet fragmentation is relatively macroscopic, and the micro interface condensation details are not well studied. In this paper, a two-dimensional multiphase computational fluid dynamics (CFD) code with the Volume of Fluid (VOF) method and solidification model is applied to simulate molten jet breakup with surface solidification. The VOF model is used to capture the interface, study the details, and add the influence of solidification. Solidification and instability can be seen at the interface. In order to simulate melt solidification, an energy equation is modeled using an enthalpy-based formulation, and viscosity variation during phase change is taken into account. The comparative results between the CFD code and jet breakup experiments show that melt jet front position histories, breakup length, and breakup time are in good agreement with the experiments. The simulation results show that crust formation of the jet surface suppresses surface instability and jet breakup behavior. As the interfacial temperature decreases, the droplet cumulative mass fraction decreases, and the solidified metal proportion increases. The simulation results by the CFD code with the solidification model are valuable and important for understanding the molten jet breakup mechanism. [ABSTRACT FROM AUTHOR]

Coaxial atomization is an established atomization strategy for many stationary combustion systems. While modeling spray formation in coaxial atomization is challenging due to the existence of a wide range of length and time scales, typical models introduce a substantial uncertainty for Euler–Lagrange simulations of the actual application, e.g., a spray flame. To reduce uncertainties, a recently proposed multiscale approach is adopted for simulations of realistic applications in this work. The multiscale approach uses three one-way coupled simulation domains that cover the internal nozzle flow, the interfacial flow of the near-field, and the dispersed flow of the far-field. The capabilities of the approach are explored by applying it to a standardized non-reacting experiment from the flame spray pyrolysis research community. In order to assess the relevance for application simulations, results are discussed in the context of mixture formation. The results are compared against shadowgraphy images of the near-field and measured droplet statistics in the far-field. It is found that the multiscale approach is capable of providing similarly accurate droplet statistics as experiments or models derived from them. In addition, it is found that the breakup dynamics in the near-field introduce substantial mixture fraction fluctuations. These fluctuations are only included because of the deterministic coupling of the multiscale approach and are typically neglected in conventional approaches. [Display omitted] • Multiscale simulations for a real coaxial atomizer are performed. • The capability of the multiscale approach is explored using experimental measurements. • The relevance of spray formation modeling limitations is highlighted. • The importance of the breakup dynamic for the mixture formation is demonstrated. [ABSTRACT FROM AUTHOR]

The capillary-driven flow is an essential portion of liquid behavior under microgravity. Capillary-driven flows in eccentric annuli under microgravity are deeply analyzed in this paper. A second-order differential equation for the climbing height of liquid is derived. It can be solved with the Runge–Kutta method with appropriate initial conditions. The influences of the dynamic angle, the friction force on the annulus wall and the liquid meniscus in the reservoir on liquid behaviors are all considered in this paper. Moreover, effects of eccentricity on flow resistance and flow speed are discussed. This study has been verified by numerical simulation with the volume of fluid method. [ABSTRACT FROM AUTHOR]

A two-phase incompressible flow model in three-dimensional cylindrical coordinates is applied for oblique wave generation in a numerical circular wave tank. The governing equations are discretized by a finite volume method, and a mass source function is added to reproduce oblique waves through a spiral wave generator positioned at the center of the tank. The volume of fluid method is implemented to track the free surfaces between the air and fluid, and the zonal embedded grid system is adopted to obtain a grid-independent solution in the cylindrical coordinates. A permeable, circumferentially sloping topography (1:7), similar to a natural beach profile, is set up for investigating wave propagation and other characteristics. The simulation and physical experimental results are compared, which show a good agreement in randomly selected water surface elevation profiles and wave heights under the same wave and sloping conditions. The spiral waves are reproduced and propagated in a phenomenon similar to that observed in the physical experiment. The results also show that the wave-breaking positions differ in different wave conditions and suggest a relationship with cross-shore and longshore velocity distribution in terms of incident wave heights and wave-breaking positions in different wave periods on the same sloping topography. Furthermore, this model can be used to investigate the mechanism of longshore current generation and the influences of beach slope on the generated wave propagation in a sloping topography. [ABSTRACT FROM AUTHOR]

The dynamics of cocurrent liquid–gas flow control the flow patterns and phase distribution inside the submerged entry nozzle (SEN) in the continuous casting. This regime transition from bubbly flow to annular flow is usually associated with a hysteresis effect that is not fully understood yet. Herein, the regime transition in an analogous liquid–gas flow is investigated using the volume of fluid (VOF) method. A downward turbulent water flow in a vertical pipe is considered as the computational domain at the top of which the gas is injected as a volumetric source in the VOF equation. By temporal variation of the gas volume rate following a linear ramp‐up and then ramp‐down, a transition from bubbly to annular flow and vice versa is observed. However, the transition occurs at different operation points and the numerical simulation pictures this hysteresis phenomenon. The regime transition is connected to the evolution of interfacial turbulence in each phase represented by the amount of vortical energy, that is, enstrophy. In addition, the temporal variation of different enstrophy generation/destruction mechanisms is evaluated. The hysteresis phenomenon is explained by the differences in the history of these mechanisms and the difference in the enstrophy generation level upon transition. [ABSTRACT FROM AUTHOR]

ObjectiveTo address the problem of wave amplitude attenuation and phase shift with respect to propagation time and distance in numerical simulation, a set of parametric design methods that can stabilize wave generation in multiple periods is given. MethodsBased on Navier-Stokes equations and volume of fluid (VOF) method, a numerical simulation of fifth-order Stokes wave is carried out. Through the analysis of the discrete scheme of the one-dimensional wave equation, the influence of several important parameters on wave-generation effect is studied. Finally, the proposed parametric design method is used to carry out the three-dimensional numerical calculation of the resistance and motion response of the KRISO container ship (KCS) in head seas. ResultsThe results show that parameters such as inner iteration times, grid resolution, and Courant number can be accurately set according to certain rules to ensure that the error of wave amplitude is about 5% within 20 wave periods and about 10% within 40 wave periods. Through the three-dimensional numerical calculation of a KCS ship, the results obtained show an error of about 10% compared with the experimental results of model, Conclusionwhich verifies the feasibility of this method.

In this paper, computational modeling of wave generation and evaluation of results are given. The analysis of Computational Fluid Dynamics is performed in the ANSYS Fluent module. The model of numerical analysis is made time-dependent. The Numerical Wave Tank is an engineering research equipment for studying sea waves that requires the least amount of people and materials. The Numerical Wave Tank may be used to simulate the motion of the ocean and sea waves with a modeled moving wall as a wave-maker. To generate regular gravity waves, a Numerical Wave Tank based on Reynolds Averaged Navier Stokes equations and the Volume of Fluid technique is modeled using Dynamic Mesh Technique. Wave heights, water depths, wavelength and wave periods are chosen variable parameters. Water volume fraction, velocities, turbulence kinetic energy and dynamic pressure are evaluated results. A brief explanation of how to generate waves influence is made.

Increasing the efficiency of hydrocarbon field development is an important issue. One of the methods for increasing oil recovery is the injection of aqueous solutions of polymers. Although this method has been known and used for quite some time, further systematic research is needed to further improve its effectiveness. In this work, systematic computational studies of the features of oil displacement by aqueous polymer solutions from a naturally fractured structure were carried out. Direct numerical modeling of a two-phase immiscible flow in the process of displacing oil from a natural fracture structure using solutions of anionic polymers based on polyacrylamide was carried out. Aqueous solutions of three different polymers were considered, the concentrations of which varied from 0 to 0.1%, and the molecular weights were from 10 to 20 mln c.u. The rheological properties of polymers and their wetting characteristics have been previously studied in laboratory experiments. A distinctive feature of the polymers considered was the non-Newtonian nature of their aqueous solutions even at low concentrations. To take these processes into account, the computational technique has been extended to the case of non-Newtonian rheology for immiscible two-phase flow in one of the media. During numerical simulations, the effect of the concentration of polymers, their molecular weight, and charging density on the flow regimes in a fractured reservoir have been investigated systematically at various crude oil viscosities. It has been shown that the use of a 0.1% aqueous solution of polyacrymalide can increase the oil-recovery factor by 1.8 times. It has been established that, with an increase in the molecular weight and surface charge density of the polymer, the efficiency of its use for enhancing oil recovery increases. With an increase in the viscosity of the displaced oil, the effect of using the injection of the considered polymers also increases. The data obtained in this work can be used to further improve polymer-flooding technologies for oil fields.

In order to quantitatively analyze the data measurement accuracy of ocean buoys under normal and extreme sea conditions, in this study, we simulated the six-degree-of-freedom motion response of self-designed ocean buoys under different sea conditions based on a separated vortex simulation and the fluid volume method and analyzed the impact of the unsteady motion of buoys on data measurement. The results indicate that under normal sea conditions, the deviation between the numerical method used in this paper and the experimental results is less than 10%. The heaving motion of a buoy is most sensitive to changes in wave conditions. The fluctuation intensity of buoy motion is modulated by the height and wavelength of waves. When the wave height and wavelength are similar to the overall geometric size of a buoy, the wave characteristics of the buoy’s heave, yaw, and pitch motion are significant. In addition, under extreme sea conditions, the movement of the buoy can also cause a deviation in the measured velocity in the transverse flow direction, but the overall deviation is less than 10%. In extreme sea conditions, the wind speed measurement results should be corrected to improve the measurement accuracy of a buoy.

Direct ink writing (DIW) belongs to material extrusion–based additive manufacturing (MEAM), and the molding quality of deposited corners has an impact on the geometrical quality of three-dimensional (3D) parts fabricated by DIW. To fully understand the DIW process and improve the geometrical quality of parts, numerical simulations have been widely used to model the DIW process. However, the previous research works for numerical simulation of deposited corners could only achieve the corner simulation under the condition of small angle and failed to realize corner simulation of any angle. Herein, an improved numerical simulation of deposited corners of any angle is proposed based on the use of volume of fluid (VOF) method and then the simulation is validated experimentally. In the numerical simulation, deposited corner is realized by constructing two calculation areas where two nozzle velocities with the corner angle are applied on the substrates of two calculation areas. The effectiveness of the proposed numerical model is validated through corner deposition experiments using a commercially available microcrystalline wax (MW)-based ink in a DIW 3D printer as the simulated corner angles fit experimental angles well and the maximum value of maximum distance deviation between simulated and experimental outlines (MDDSEO) is 1.06 ± 0.06 mm. It was observed that the MDDSEO of corners is larger than MDDSEO of straight filaments and decreases as corner angle increases. The current work demonstrates an effective approach for the prediction of the deposited corners of any angle in DIW based on numerical simulations. [ABSTRACT FROM AUTHOR]

A two-bubble model with radiate (α bubble)-receive (β bubble) structure is constructed to study the energy transfer from one bubble to another. The influence of the non-dimensional distance d and the initial energy ratio ψ on the energy transfer rate is investigated via numerical simulation. The relative received energy ε, relative jet energy J, and energy transfer rates η are defined to quantify energy transfer. Results show that the energy transfer rate decreases with the increase of d and ψ when the two bubbles’ initial radius is identical. With the increase of d, the interactions between two bubbles are weakened, and the relative received energy satisfies the law of ε ∝ 1/d2. With the increase of ψ, the maximum inner pressure of the β bubble increase first and then decreases, while the jet energy of bubble β changes with the law of J ∝ ψ. It is found that the energy storage capacity increases with the bubble radius by simulating different bubble radius ratios. [ABSTRACT FROM AUTHOR]

Performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA≤30° at a Reynolds number of 105. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

Benchmarking can be used to test CFD programs for selecting turbulence models, grid dependency studies, testing different numerical schemes and source codes, and testing different boundary conditions. CFD simulation in this study uses FINE™/Marine 7.2-1 software. The solver process at NUMECA uses the ISIS-CFD flow solver developed by EMN, which uses the incompressible unsteady Reynolds-average Navier stoke equation (RANSE). The solver is based on the finite volume method, and Turbulence models use SST k-ω models. The free surface flow around a model surface ship (DTMB 5415) advancing in calm water under steady conditions is numerically simulated. The geometry of the DTMB 5415 ship hull was provided in igs file format. The 1996 International Towing Tank Conference has recommended the DTMB 5415 combatant as a benchmark case for CFD computations of ship resistance and propulsion. The results compare well with the available experimental data. They allow an understanding of the differences that can be expected from vicious and potential flow methods due to their different mathematical formulations. It is demonstrated that the complementary application of these methods allows good predictions of the total ship resistance.