Volume Of Fluid Model Research Articles

Multiphase Flow Modeling of Slag Entrainment During Ladle Change-Over Operation

Steel transfer from the ladle to a single-strand tundish using a conventional ladle shroud (CLS), and a dissipative ladle shroud (DLS) is studied during the transient period of ladle change-over operation. Fluid velocities and fluid flow turbulence statistics during this unsteady operation were recorded by an ultrasound velocimetry probe in a 1/3 scale water–oil–air analog model (to emulate steel-slag-air system). Reynolds stress model and volume of fluid model allow the tracking of water–oil, water–air, and oil-air interfaces during this operation. Velocity measurements indicate a very high turbulence with the formation of a water–air bubbles-oil emulsion. Flow turbulence and the intensity of the emulsification decrease considerably due to an efficient dissipation of the turbulent kinetic energy employing the DLS instead of the CLS. The modeling results indicate that DLS is widely recommended to substitute flow control devices to improve the fluid dynamics of liquid steel during this transient operation.

3D CFD validation of invert trap efficiency for sewer solid management using VOF model

Earlier investigators have numerically carried out performance analysis of the invert trap fitted in an open channel using the stochastic discrete phase model (DPM) by assuming the open channel flow to be closed conduit flow under pressure and assuming zero shear stress at the top wall. This is known as the fixed lid model. By assuming the top wall to be a shear free wall, they have been able to show that the velocity distribution looks similar to that of an open channel flow with zero velocity at the bottom and maximum velocity at the top, representing the free water surface, but no information has been provided for the pressure at the free water surface. Because of this assumption, the validation of the model in predicting the trap efficiency has performed significantly poorly. In addition, the free water surface subject to zero gauge pressure cannot be modeled using the fixed lid model because there is no provision of extra space in the form of air space for the fluctuating part of the water surface profile. It can, however, be modeled using the volume of fluid (VOF) model because the VOF model is the appropriate model for open channel or free surface flow. Therefore, in the present study, three-dimensional (3D) computational fluid dynamics (CFD) modeling with the VOF model, which considers open channel flow with a free water surface, along with the stochastic DPM, was used to model the trap efficiency of an invert trap fitted in an open rectangular channel. The governing mathematical flow equations of the VOF model were solved using the ANSYS Fluent 14.0 software, reproducing the experimental conditions exactly. The results show that the 3D CFD predictions using the VOF model closely fit the experimental data for glass bead particles.

Determination for the Entrapment Criterion of Non-metallic Inclusions by the Solidification Front During Steel Centrifugal Continuous Casting

In the current study, the three-dimensional fluid flow, heat transfer, and solidification in steel centrifugal continuous casting strands were simulated. The volume of fluid model was used to solve the multiphase phenomena between the molten steel and the air. The entrapment and final distribution of inclusions in the solidified shell were studied with the discussion on the effect of rotation behavior of the caster system. Main results indicate that after applying the rotation of the shell, the fluid flow transformed from a recirculation flow to a rotation flow in the mold region and was driven to flow around in the casting direction. As the distance below the meniscus increased, the distribution of the tangential speed of the flow and the centrifugal force along one diameter of the strand became symmetrical gradually. The jet flow from the nozzle hardly impinged on the same location on the shell due to the rotation of the shell during solidification. Thus, the shell thickness on the same height was uniform around, and the thinning shell and a hot spot on the surface of shell were avoided. Both of the measurement and the calculation about the distribution of oxide inclusions along the radial direction indicated the number of inclusions at the side and the center was more than that at the quarter on the cross section of billet. With a larger diameter, inclusions tended to be entrapped toward the center area of the billet.

Comprehensive Mathematical Model for Simulating Electroslag Remelting

Droplet formation and departure from an electrode tip affect the temperature distribution in liquid slag and a molten steel pool, as well as the removal of nonmetallic inclusions in the electroslag remelting process. In this article, magneto-hydrodynamics modules coupled with a volume of fluid (VOF) model (as described in VOF model theory) for tracking phase distribution have been employed to develop the electrode fusion model and to investigate formation and departure of a droplet from the electrode tip. Subsequently, the remelting rate and molten steel pool have been achieved based on the electrode fusion model. Results indicate that a droplet can increase the flow rate of liquid slag, especially the region of droplet fall through the slag pool; yet it has little impact on the flow distribution. Asymmetric flow can take place in a slag pool due to the action of the droplet. The depth of the molten steel pool increases in the presence of droplets, but the width of the mushy zone decreases. In addition, the shape of the electrode tip is not constant but changes with its fusion. The remelting rate is calculated instead of being imposed in this work. The development of the model supports further understanding of the process and the ability to set the appropriate operating parameters, especially for expensive and easy segregation materials.

Computational Simulation and Experimental Research of Flow Rates in Coaxial Fluids for Fabricating Hydrogel Fibers

As one of the biomanufacturing technologies, 3D bioprinting is becoming one effective way to solve the issues in tissue engineered constructs. In order to produce 3D cell-laden scaffolds to overcome the main technological barrier in cell distribution and nutrient supply and better mimic the in vivo cellular environment, hydrogel fibers were used to deposit in 3D bioprinting system and obtain the 3D cell-laden hydrogel structures. In the present work, we investigate the effects of flow rates on the dimensions of hydrogel fibers. The volume of fluid model by the computational fluid dynamics software package FLUENT 6.3.26 is applied to obtain the appropriate flow rates to produce hydrogel fibers. Different flow pattern in the coaxial model is obtained. In addition, a coaxial nozzle was used to fabricate hydrogel fibers under various flow rates to know its’ effects on the dimension of hydrogel fibers.

A Novel Volume of Fluid Model for Numerical Simulation of Wettability of Falling Film over Horizontal Tubes

A Novel Volume of Fluid Model for Numerical Simulation of Wettability of Falling Film over Horizontal Tubes

Hydrodynamics of novel structured packings: An experimental and multi-scale CFD study

Three types of structured packings with wave-like corrugated sheets were investigated, aiming to improve the hydrodynamics of structured packings. The experimental results showed that the new proposed structured packings have a significant advantage in pressure drop and capacity over traditional Mellapak 125X. A modified multi-scale CFD (computational fluid dynamic) model was applied to characterize the hydrodynamic performance of the novel packings. At the micro-scale (corrugation scale), a 2D VOF (volume of fluid) model was used to trace the gas–liquid interface and to calculate the liquid film thickness for two-phase flow; then, a 3D VOF model was used to calculate the effective wetting area at the meso-scale (packing element scale). Finally, a 3D porous media model was proposed to calculate the dry and wet pressure drops at the macro-scale (column scale). The average relative deviations between the experimental data and the calculated results for dry and wet pressure drops were 7.26% and 8.24%, respectively, confirming validity of the CFD simulations. The proposed modified multi-scale CFD model can be used effectively to design and optimize complex structured packings.

A 2D-CFD (VOF model) analysis of invert trap for bed load removal in an open rectangular sewer drain

ABSTRACTTo optimize the hydraulic efficiency of sewers or storm water drainage systems, it is necessary to trap the flowing sediments at suitable channel sections using a number of available means. Invert trap is one of the many available means used for trapping the flowing sediments. To analyze the effect of different parameters on the trap efficiency of an invert trap, experimentation is required. As experimentation is always not possible or becomes a costly affair, computational fluid dynamics (CFD) has now become an excellent useful and less expensive tool for the study of flow in sewers and storm water drainage systems. In the present study, a 2D-CFD analysis with volume of fluid (VOF) model, using ANSYSFluent14.0 software, has been performed to predict the trap efficiency of the invert trap for varying flow, particle, and geometrical parameters. The analysis shows that the CFD-VOF model predicts excellent trap efficiency for glass beads of 0.3 mm diameter as compared to the experimental trap efficiency of Thinglas (2008) with mean absolute percentage error (MAPE) of 5.54%, whereas it predicted higher trap efficiencies for sand particles of diameter equal (= d50) to 0.15 mm for which the numerically justified reasons are stated.

Design and Optimization for the Windowless Target of the China Nuclear Waste Transmutation Reactor

A windowless spallation target can provide a neutron source and maintain neutron chain reaction for a subcritical reactor, and is a key component of China's nuclear waste transmutation of coupling accelerator and subcritical reactor. The main issue of the windowless target design is to form a stable and controllable free surface that can ensure that energy spectrum distribution is acquired for the neutron physical design when the high energy proton beam beats the lead–bismuth eutectic in the spallation target area. In this study, morphology and flow characteristics of the free surface of the windowless target were analyzed through the volume of fluid model using computational fluid dynamics simulation, and the results show that the outlet cross section size of the target is the key to form a stable and controllable free surface, as well as the outlet with an arc transition. The optimization parameter of the target design, in which the radius of outlet cross section is 60 ± 1 mm, is verified to form a stable and controllable free surface and to reduce the formation of air bubbles. This work can function as a reference for carrying out engineering design of windowless target and for verification experiments.

Pressure distribution and flow characteristics of closed oscillating heat pipe during the starting process at different vacuum degrees

This work is focused on the distribution and fluctuation of pressure, vapor flow patterns, and the relationship between them during the starting process at different vacuum degrees of closed oscillating heat pipe (COHP). A two-dimensional model of the closed oscillating heat pipe was established, and the VOF (volume of fluid) model was taken as the solution to carry out the numerical simulation of liquid–vapor during the two-phase conversion. The relationships of pressure distribution and vapor flow patterns were analyzed and a series of visualization experimental results were used to compare with simulation ones. It shows that both of them are highly consistent. The laws obtained from start-up analysis and contrast of simulation and experiment are beneficial to research the oscillating heat pipe in the future.

Numerical investigation on the velocity fields during droplet formation in a microfluidic T-junction

In this paper, we present the findings from a numerical investigation of the droplet formation process in a T-junction microchannel. A volume-of-fluid (VOF) model that is refined with smoothing operations was used to minimise spurious or non-physical velocities at the micro-scale, in order to obtain more accurate velocity results from the microchannel simulations. The model was validated with experimental results and was able to yield a closer match to the experimental data compared to the standard VOF model. Subsequently the refined VOF model was used to investigate the velocity field evolution during the droplet formation process to further understand the underlying physics. For the squeezing regime, we observed regions of large recirculation after droplet break-up with reversed flows. These recirculation regions were also seen in the transition and dripping regimes but reversed flows did not occur. We also studied the effects of varying the dispersed phase flow rate under a constant capillary number (Ca) of the continuous phase. The results show that increasing the dispersed phase flow increases the droplet length and formation frequency. In addition, the frequency of the velocity fluctuation at the junction vicinity was found to coincide with the rate of new droplet formation. Finally, the effects of Weber number on droplet length was also investigated and it was found that inertial forces significantly influence droplet formation, albeit being the least dominant force.

Constructal Design de um dispositivo de galgamento onshore em escala real para uma profundidade fixa

O estudo a respeito das tecnologias e princípios de funcionamento de dispositivos de conversão de energia das ondas em energia elétrica (WEC) tem crescido sensivelmente. Entre os WECs estudados está o dispositivo de galgamento. O seu princípio físico de funcionamento consiste em uma rampa que guia a água das ondas incidentes para um reservatório localizado acima do nível médio do mar. A água acumulada no reservatório escoa através de uma turbina de baixa queda gerando energia elétrica. No presente trabalho é realizado um estudo numérico relacionado ao efeito da geometria da rampa sobre o desempenho de um dispositivo de galgamento <em>onshore</em> em escala real, empregando <em>Constructal Design</em>. O principal propósito aqui é avaliar a razão entre altura e comprimento da rampa (<em>H</em><sub>1</sub>/<em>L</em><sub>1</sub>) que maximiza a quantidade de água que entra no reservatório do dispositivo para uma distância entre o fundo do dispositivo e o fundo do tanque de <em>S</em> = 6.0 m. Nas presentes simulações, as equações de conservação de massa, quantidade de movimento e uma equação para o transporte da fração volumétrica são resolvidas com o método dos volumes finitos (MVF). Para abordar a mistura água e ar, o modelo multifásico <em>Volume of Fluid</em> (VOF) é empregado. Os resultados mostraram que as melhores geometrias são obtidas para as menores razões de <em>H</em><sub>1</sub>/<em>L</em><sub>1</sub> para a profundidade analisada, contrariamente ao que foi observado em estudos preliminares da literatura para um dispositivo no meio do canal em escala de laboratório que simulava um dispositivo de galgamento do tipo <em>offshore</em>.

Simulation and experiment on transitional behaviours of multiphase flow in a hydrocyclone

This paper presents an investigation of transitional behaviours of multiphase flow in a hydrocyclone. The experiment and simulation results reveal the existence of two stages of the transition period of gas‐liquid flow. The numerical model combined with the large eddy simulation model (LES), the volume of fluid model (VOF), and the Lagrangian discrete phase model (DPM) approach is used to simulate the multiphase flow in a hydrocyclone. The applicability of this approach with a 2‐step simulation strategy has been verified by the close agreement between the calculated and measured flow fields. Particle motion upon entering the hydrocyclone indicates the separation mechanism of a hydrocyclone. Moreover, a parameter of the hydrocyclone, separation cycle timeTc, is proposed to describe the dynamic characteristics of the particle residence time.

Coupling a local adaptive grid refinement technique with an interface sharpening scheme for the simulation of two-phase flow and free-surface flows using VOF methodology

This study presents the implementation of an interface sharpening scheme on the basis of the Volume of Fluid (VOF) method, as well as its application in a number of theoretical and real cases usually modelled in literature. More specifically, the solution of an additional sharpening equation along with the standard VOF model equations is proposed, offering the advantage of “restraining” interface numerical diffusion, while also keeping a quite smooth induced velocity field around the interface. This sharpening equation is solved right after volume fraction advection; however a novel method for its coupling with the momentum equation has been applied in order to save computational time. The advantages of the proposed sharpening scheme lie on the facts that a) it is mass conservative thus its application does not have a negative impact on one of the most important benefits of VOF method and b) it can be used in coarser grids as now the suppression of the numerical diffusion is grid independent. The coupling of the solved equation with an adaptive local grid refinement technique is used for further decrease of computational time, while keeping high levels of accuracy at the area of maximum interest (interface). The numerical algorithm is initially tested against two theoretical benchmark cases for interface tracking methodologies followed by its validation for the case of a free-falling water droplet accelerated by gravity, as well as the normal liquid droplet impingement onto a flat substrate. Results indicate that the coupling of the interface sharpening equation with the HRIC discretization scheme used for volume fraction flux term, not only decreases the interface numerical diffusion, but also allows the induced velocity field to be less perturbed owed to spurious velocities across the liquid–gas interface. With the use of the proposed algorithmic flow path, coarser grids can replace finer ones at the slight expense of accuracy.

Numerical Simulation on BLEVE Mechanism of Supercritical Carbon Dioxide

Abstract Greenhouse effect and energy shortage is becoming a more and more serious problem with the fast development of oil refining industry. Oil carbon capture and storage and the enhanced oil recovery (CCS-EOR) is developed to cover the shortage. A simulation was made by CFD method in this paper. The FLUENT software was utilized, and the SIMPLEC method and standard turbulent model are adopted to solve compressible N-S equations. VOF (Volume of Fluid) model are chosen as multiphase model. Numerical simulation is based on physical model and suitable mathematical model. A model was established to illustrate Mechanism and regulation of Supercritical CO 2 BLEVE which can provide technical support to accident prevention and be used as reference for future research.

Computational and experimental investigations of the mechanisms used by coaxial fluids to fabricate hollow hydrogel fibers

Biological three-dimensional printing is a promising field of research, and offers potential for overcoming the main technological barriers to the fabrication of three-dimensional vascularized tissues and organs. One of the major methods to fabricate vascular-like networks that can support perfusion of nutrients and oxygen is the printing of hollow hydrogel fibers. In the present work, we investigate the effects of operating conditions on the dimensions of hollow hydrogel fibers and the interaction mechanism of coaxial fluids. The continuity equation and momentum equation integrated with the reaction–diffusion model established by Kim et al. [1] are used to establish a mathematical model of the fabrication of hollow fibers from coaxial fluids. The volume of fluid model by the computational fluid dynamics software package FLUENT 6.3.26 is applied to quantitatively simulate the flow pattern details. A stable liquid/liquid jetting co-laminar flow in the coaxial nozzle is obtained. In order to verify the validity of the simulation model, a coaxial nozzle is used to fabricate hollow hydrogel fibers under various flow rates. The results from simulations and experiments are consistent with each other.

Numerical simulation of the stokes wave for the flow around a ship hull coupled with the VOF model

The surface wave generated by flow around a ship hull moving near free surface of water is simulated numerically in this study. The three-dimensional implicit finite volume method (FVM) is applied to solve Reynolds averaged Navier-Stokes (RANS) equation. The realizable k-e turbulence model has been implemented to capture turbulent flow around the ship hull in the free surface zone. The volume of fluid (VOF) method coupled with the Stokes wave theory has been used to determine the free surface effect of water. By using is a six degrees of freedom model, the ship hull’s movement is numerically solved with the Stokes wave together. Under the action of Stokes waves on the sea, the interface between the air and water waves at the same regular pattern and so does the pressure and the vertical velocity. The ship hull moves in the same way as the wave. The amplitude of the ship hull’s heave is less than the wave height because of the viscosity damping. This method could provide an important reference for the study of ships’ movement, wave and hydrodynamics.

Droplet–wall interaction upon impingement of heavy hydrocarbon droplets on a heated wall

Regime maps that predict the heavy hydrocarbon droplet impingement behavior on a heated wall (Weber number of the impinging droplet v/s wall temperature) are constructed based on CFD simulations using the Volume of Fluid model with the geo-reconstruct scheme. Based on the simulation results, maps are constructed for single-component droplets with a diameter of 50 and of 100µm. The applied CFD model is validated by comparing these with regime maps available in literature, constructed based on experimental data for model liquids and liquid mixtures. The impingement regimes of Splash, Stick, Rebound and Breakup are well-predicted. Two distinct types of Splash (Splash with ligament formation and Splash with ring detachment) are reported for the first time. Using the validated CFD model, regime maps are constructed for multi-component heavy hydrocarbon droplets with a diameter of 50 and of 100µm. Significant differences between the single-component and the multi-component droplet impact behavior are observed. Improved and new correlations for regime transitions, droplet stretching on the wall, droplet rebounding velocity and number of splashed droplets are derived based on energy balances. They are found to correlate well with CFD predictions.

Numerical Analysis including Pressure Drop in Oscillating Water Column Device

AbstractThe wave energy conversion into electricity has been increasingly studied in the last years. There are several proposed converters. Among them, the oscillatingwater column (OWC) device has been widespread evaluated in literature. In this context, the main goal of this work was to perform a comparison between two kinds of physical constraints in the chimney of the OWC device, aiming to represent numerically the pressure drop imposed by the turbine on the air flow inside the OWC. To do so, the conservation equations of mass,momentumand one equation for the transport of volumetric fraction were solved with the finite volume method (FVM). To tackle thewater-air interaction, the multiphase model volume of fluid (VOF)was used. Initially, an asymmetric constraint inserted in chimney duct was reproduced and investigated. Subsequently, a second strategywas proposed,where a symmetric physical constraint with an elliptical shapewas analyzed. Itwas thus possible to establish a strategy to reproduce the pressure drop in OWC devices caused by the presence of the turbine, as well as to generate its characteristic curve.

Horizontal jet characteristics of an underwater solid rocket motor at the beginning of working

Compared with the conventional solid rocket motor which works in atmosphere, the underwater solid rocket motor has different performance characteristics, because the buoyancy of water cannot be neglected, while in the atmosphere only gravity is present. In order to get a deep understanding of the mechanism of thrust oscillation characteristics and of the jet structure of underwater solid rocket motor, a 3-D numerical simulation using the volume of fluid (VOF) model is given in this paper to investigate the horizontal jet structure and the oscillating flow field induced by the gravity and buoyance. The principle of momentum is carried out to analyze the oscillating flow field in the initial working period. Result of analysis indicates that the behavior of rising gas bubbles is remarkably influenced by gravity and buoyancy. Compared to the conventional solid rocket motor in the atmosphere environment, the phenomenon shows that the rising gas bubbles are more obvious in the water. It is concluded that thrust-gravity and buoyancy coupling can generate bigger roll moment in the vertical direction than the conventional solid rocket motor. Numerical calculations in conjunction with experiment in the references proves that the model contains gravity, buoyancy and the VOF model can be used to describe the jet structure and thrust oscillation of underwater solid rocket motor; gravity and buoyancy cannot be ignored in the research of underwater solid rocket motor performance characteristics.