Showing papers on "Volume of fluid method published in 2006"
TL;DR: It is demonstrated that a flow algorithm designed to legislate force balance retains an exact balance between surface tension forces and the resulting pressure gradients for both continuous and sharp representations of interfacial surface tension.
676 citations
15 Aug 2006
TL;DR: Variable contact angle values around the gas-liquid-solid contact-line as well as their dynamic change during the droplet shape deformation process, have allowed estimation of the adhesion force between the liquid droplet and the solid surface and successful prediction of the separation line.
Abstract: The detachment of liquid droplets from porous material surfaces used with proton exchange membrane (PEM) fuel cells under the influence of a cross-flowing air is investigated computationally and experimentally. CCD images taken on a purpose-built transparent fuel cell have revealed that the water produced within the PEM is forming droplets on the surface of the gas-diffusion layer. These droplets are swept away if the velocity of the flowing air is above a critical value for a given droplet size. Static and dynamic contact angle measurements for three different carbon gas-diffusion layer materials obtained inside a transparent air-channel test model have been used as input to the numerical model; the latter is based on a Navier-Stokes equations flow solver incorporating the volume of fluid (VOF) two-phase flow methodology. Variable contact angle values around the gas-liquid-solid contact-line as well as their dynamic change during the droplet shape deformation process, have allowed estimation of the adhesion force between the liquid droplet and the solid surface and successful prediction of the separation line at which droplets loose their contact from the solid surface under the influence of the air stream flowing around them. Parametric studies highlight the relevant importance of various factors affecting the detachment of the liquid droplets from the solid surface.
264 citations
TL;DR: In this article, the capabilities of three volume-of-fluid methods for the calculation of surface tension-dominant two-phase flows are tested, and the analytical solutions for each problem serve to examine the accuracy and the convergence behavior of each approach.
252 citations
TL;DR: In this article, the shape and velocity of the slug, the velocity distribution and the distribution of local wall shear stress were computed and compared favourably with the published experimental findings.
241 citations
TL;DR: In this article, an attempt is made to model slug flow inside square capillaries containing Newtonian liquids and a comprehensive description of such flow is obtained and a comparative study is conducted.
177 citations
TL;DR: Different from previous works, this work has developed an analytic method for finding the line constant on triangular grids, which makes interface reconstruction efficient and conserves volume of fluid exactly.
170 citations
TL;DR: In this article, a numerical algorithm based on the volume of fluid (VOF) technique is used to study the non-linear behavior and damping characteristics of liquid sloshing in a moving partially filled rectangular tank.
163 citations
TL;DR: In this article, the authors derived and validated a correlation for the magnitude of these currents as a function of the physical and numerical parameters used in a given simulation, and found that these currents may be limited by both the inertial and viscous terms in the Navier-Stokes equations, and they do not decrease in magnitude with increased mesh refinement or decreased computational time step.
160 citations
TL;DR: In this paper, an attempt has been made to develop a CFD (computational fluid dynamics) model which is capable of predicting the flow patterns inside the hydrocyclone, including accurate prediction of flow split as well as the size of the air-core.
110 citations
TL;DR: A numerical model is presented for the simulation of viscoelastic flows with complex free surfaces in three space dimensions and results pertaining to jet buckling are reported.
109 citations
TL;DR: In this paper, a volume of fluid (VOF) technique was developed and coupled with an incompressible Euler/Navier-Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures.
TL;DR: Using the volume of fluid (VOF) method, a numerical model is developed to estimate the nonlinear dynamics of a pontoon type moored submerged breakwater under wave action as discussed by the authors.
TL;DR: In this article, the hydrodynamics of liquid flow in packed columns were investigated in a single structured and flat packing element of Rombopak 4M, which consists of four connected wavy inclined plates in an X-shape configuration.
Abstract: The hydrodynamics of liquid flow in packed columns affects the column performance from the point of view of heat and mass transfer. The interfacial and the specific wetted areas are decisive in this case. The complex three-dimensional liquid flow on a single structured and flat packing element of Rombopak 4M was investigated. It consists of four connected wavy inclined plates in an X-shape configuration. The geometric characteristics of the packing were related to the fluid mechanics of the liquid distribution. CFD simulation results for different cell sizes and flow rates, obtained using the VOF (volume of fluid) model, are presented as being capable of describing this complex geometry. With the help of the CFD simulation and the experimental results from Rombopak 4M, correlations from the literature describing the interfacial and wetted area and liquid holdup in packed columns were adjusted to describe the hydrodynamic performance of Rombopak 4M.
TL;DR: In this article, the authors carried out an axisymmetric numerical investigation of the evolution of large gas bubbles in the presence of both capillary and viscous effects, and found that initially oblate bubbles may result in stable spherical cap bubbles for values of Bo and Archimedes numbers.
Abstract: Large gas bubbles rising under the effect of buoyancy are known to adopt either a spherical cap shape or to undergo a topological transition after which they become toroidal. We carry out an axisymmetric numerical investigation of the evolution of such large bubbles in the presence of both capillary and viscous effects. The numerical approach is of the volume of fluid type (it solves the Navier-Stokes equations on a fixed grid and transports the local volume fraction of one of the fluids), but does not involve any explicit reconstruction of the interface. The transition from spherical cap to toroidal bubbles is studied in the parameter space built on the Bond (Bo) and Archimedes (Ar) numbers, which compare the strength of inertial effects to that of capillary and viscous effects, respectively. Preliminary tests show that the position of this transition is very sensitive to the grid resolution; these tests are used to select grid characteristics that yield grid-independent results. Two markedly different transition scenarios, corresponding to the limit of large Ar and large Bo, respectively, are then identified. In the first case, the front of the bubble is pierced by an upward jet coming from the rear of the bubble. In contrast, in the limit of large Bo, a downward jet develops at the front part and pierces the rear of the bubble, unless viscous effects are sufficient to stabilize the front. We also determine the position of the transition for intermediate values of Bo and Ar and discuss the connection between present axisymmetric results and experimental situations in which the bubble is followed by a turbulent wake. We finally examine a puzzling feature of these large bubbles which is that, given an initial gas volume, the final bubble topology appears to depend dramatically on the initial conditions. Indeed, we find that initially oblate bubbles may result in stable spherical cap bubbles for values of Bo and Ar well beyond those for which initially spherical bubbles of similar volume undergo the topological transition. This remarkable influence of the initial shape is shown to be due to the influence of the oblateness on both the bubble acceleration and the hydrostatic pressure difference between the two bubble poles.
TL;DR: In this article, the feasibility of CFD modeling of the Taylor flow regime in capillaries by using the volume-of-fluid (VOF) technique for the motion of the gas−liquid interphase is examined.
Abstract: Taylor flow, a flow regime characterized by Taylor bubbles separated by liquid slugs that do not contain entrained micro bubbles, is a predominant gas−liquid two-phase flow regime in capillaries and minichannels (channels with hydraulic diameters in the 0.1−1 mm range), and it occurs in monolithic catalytic converters and other multiphase reactors. Taylor flow regime is morphologically relatively simple and has been modeled in the past using computational fluid dynamics (CFD) methods. However, most of the past CFD models have either assumed a fixed gas−liquid interfacial geometry or have modeled the gas−liquid interphase movement based on the method of spines, which imposes some restrictions on the free movement of the interface. In this study, we examine the feasibility of CFD modeling of the Taylor flow regime in capillaries by using the volume-of-fluid (VOF) technique for the motion of the gas−liquid interphase. It is shown that such a model predicts well the experimental data and empirical correlation...
TL;DR: In this paper, the deformation of the gas-liquid interface is modelled by the pressure jump across the interface via the Young-Laplace equation and the governing equations in the axisymmetric cylindrical coordinates are solved using the commercial CFD code, FLUENT.
TL;DR: In this article, the Navier-Stokes equations for two-dimensional incompressible flow are solved in a periodic domain, and a volume-of-fluid method is used to track the interface.
Abstract: We perform numerical simulations of two-phase liquid–gas sheared layers, with the objective of studying atomization. The Navier–Stokes equations for two-dimensional incompressible flow are solved in a periodic domain. A volume-of-fluid method is used to track the interface. The density ratio is kept around 10. The calculations show good agreement with a fully viscous Orr–Sommerfeld linear theory over several orders of magnitude of interface growth. The nonlinear development shows the growth of finger-like structures, or ligaments, and the detachment of droplets. The effect of the Weber and Reynolds numbers, the boundary layer width and the initial perturbation amplitude are discussed through a number of typical cases. Inversion of the liquid boundary layer is shown to yield more readily ligaments bending upwards and is thus more likely to produce droplets.
TL;DR: In this article, the authors developed a volume of fluid (VOF)-based two-phase flow model and discussed the applicability of the model to the simulation of wave-structure interactions.
TL;DR: This paper presents analytical relations connecting linear interfaces and volume fractions in triangular and tetrahedral grids and cites some of the most efficient formulas for polygon area and polyhedron volume computations for computing the volume of fluid in an arbitrary polygonal or polyhedral fluid element.
TL;DR: In this article, the SIMPLE algorithm using a volume of fluid (VOF) method is adopted to investigate the flows in those microchannels, and the flow characteristics such as the liquid front shapes and the evolution of the liquid lengths are obtained.
Abstract: Capillary flows inside microchannels with patterned-surfaces are investigated theoretically and numerically. The surface energy method is used to derive an equivalent contact angle (ECA) model for small capillary number flows. The SIMPLE algorithm using a volume of fluid (VOF) method is adopted to investigate the flows in those microchannels. The flow characteristics such as the liquid front shapes and the evolution of the liquid lengths are obtained. The numerical results reveal that capillary flows in a patterned-surface microchannel still follow the traditional capillary theories. The ECA model is confirmed by the numerical results. It indicates that the capillary flows inside the patterned-surface microchannels can be estimated by means of the homogeneous-surface microchannels with the equivalent contact angle. The ECA model provides a good criterion for the total wettability of a patterned-surface microchannel, as well.
TL;DR: In this article, numerical simulations were conducted to investigate how a droplet of a higher viscosity Newtonian liquid behaves when passing through an axisymmetric microfluidic contraction.
TL;DR: In this article, a numerical simulation of floating or submerged body motions is presented based on a volume of fluid (VoF)-fractional step coupling, which can be extended for full nonlinear motion of ships in waves.
TL;DR: In this article, the effects of mesh motion on the stability of fluid-flow equations when written in an arbitrary Lagrangian-Eulerian frame for solving moving boundary flow problems are investigated.
Abstract: This paper investigates the effects of mesh motion on the stability of fluid-flow equations when written in an Arbitrary Lagrangian–Eulerian frame for solving moving boundary flow problems. Employing the advection-diffusion equation as a model problem we present a mathematical proof of the destabilizing effects induced by an arbitrary mesh motion on the stability and convergence of an otherwise stable scheme. We show that the satisfaction of the so-called geometric conservation laws is essential to the development of an identity that plays a crucial role in establishing stability. We explicitly show that the advection dominated case is susceptible to growth in error because of the motion of the computational grid. To retain the bound on the growth in error, the mesh motion techniques need to account for a domain based constraint that minimizes the relative mesh velocity. Analysis presented in this work can also be extended to the Navier–Stokes equations when written in an ALE frame for FSI problems.
TL;DR: In this article, a numerical model for predicting waves generated by nearshore submarine mass-movements is described, which is based on the Reynolds Averaged Navier Stokes (RANS) equations with the k - e turbulence model.
TL;DR: In this paper, a volume of fluid (VOF) technique was further developed and coupled with an incompressible Euler/Navier Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and a LNG carrier with full or partially filled tanks.
Abstract: A Volume of Fluid (VOF) technique has been further developed and coupled with an incompressible Euler/Navier Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and a LNG carrier with full or partially filled tanks. The present implementation follows the classic VOF implementation for the liquid-gas system, considering only the liquid phase. Extrapolation algorithms are used to obtain velocities and pressures in the gas region near the free surface. An arbitrary Lagrangian-Eulerian (ALE) frame of reference is used. The mesh is moved in such a way as to minimize the distortion of the mesh due to body movement. The incompressible Euler/Navier-Stokes equations are solved using projection schemes and a finite element method on unstructured grids, and the free surface is captured by the VOF method. The computer code developed based on the method described above is used in this study to simulate a numerical seakeeping tank, where the waves are generated by the sinusoidal excitation of a piston paddle, and a freely-floating LNG carrier with full or partially filled tanks moves in response to the waves. Both head sea and oblique sea are considered in the simulation. Highly nonlinear wave-body interactions, such as green water on deck and sloshing, have been modeled successfully.
01 Feb 2006-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the critical bath level or bath height for this phenomenon is 0.35 m (in this particular ladle design) for a ladle standstill time of 15 minutes and decreases with longer standstill times.
Abstract: Fluid flow dynamics during ladle drainage operations of steel under isothermal and nonisothermal conditions has been studied using the turbulence shear stress transport k-e model (SST k-ω) and the multiphase volume of fluid (VOF) model. At high bath levels, the angular velocity of the melt, close to the ladle nozzle, is small rotating anticlockwise and intense vertical-recirculating flows are developed in most of the liquid volume due to descending steel streams along the ladle vertical wall. These streams ascend further downstream driven by buoyancy forces. At low bath levels, the melt, which is close to the nozzle, rotates clockwise with higher velocities whose magnitudes are higher for shorter ladle standstill times. These velocities are responsible for the formation and development of a vortex on the bath free surface, which entrains slag into the nozzle by shear-stress mechanisms at the metal-slag interface. The critical bath level or bath height for this phenomenon is 0.35 m (in this particular ladle design) for a ladle standstill time of 15 minutes and decreases with longer ladle standstill times. At these steps, the vertical-recirculating flows are substituted by complex horizontal-rotating flows in most of the liquid volume. Under isothermal conditions, the critical bath level for vortex formation on the melt free surface is 0.20 m, which agrees very well with that determined with a 1/3 scale water model of 0.073 m. It is concluded that buoyancy forces, originated by thermal gradients, as the ladle cools, are responsible for increasing the critical bath level for vortex formation. Understanding vortex mechanisms will be useful to design simple and efficient devices to break down the vortex flow during steel draining even at very low metal residues in the ladle.
05 Nov 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the axisymmetric model was developed to study the interaction between the flow in the inter-tow space and that in the intra-tows space.
Abstract: The resin transfer molding has gained popularity in the preparation of fiber-reinforced polymer-matrix composites because of its high efficiency and low pollution. The non-uniform inter-tow and intra-tow flows are regarded as the reason of void formation in RTM. According to the process characteristics, the axisymmetric model was developed to study the interaction between the flow in the inter-tow space and that in the intra-tow space. The flow behavior inside the fiber tows was formulated using Brinkman's equation, while that in the open space around the fiber tows was formulated by Stokes' equation. The volume of fluid (VOF) method was applied to track the flow front, and the effects of filling velocity, resin viscosity, inter-tow dimension and intra-tow permeability on fluid pressure and flow front were analyzed. The results show that the flow front difference between the inter-tow and intra-tow becomes larger with the decrease of intra-tow permeability, as well as the increase of filling velocity and inter-tow dimension.
TL;DR: In this paper, the authors use a two-dimensional potential flow model to find the pulse volumes that optimize mixing in a rectangular domain containing two source-sink pairs, a system of current interest in DNA microarray analysis.
Abstract: Fluid mixing in a Hele–Shaw cell can be accomplished by periodically pulsing pairs of sources and sinks. The mixing efficiency of this system depends largely on the volume of fluid that is injected (and extracted) during each pulse. In this paper, the authors use a two-dimensional potential flow model to find the pulse volumes that optimize mixing in a rectangular domain containing two source–sink pairs, a system of current interest in DNA microarray analysis. Optimal mixing protocols are identified by determining maximum entropy using an analysis of chaotic advection.
TL;DR: In this article, a volume-of-fluid (VOF) method with piecewise linear interface construction (PLIC) technique was used to describe the behavior of interfacial movements.
Abstract: The goal of this study is to explore the liquid ejection behavior for a Picojet® printhead. In the computational approach, the theoretical model adopted the transient three-dimensional conservation equations of mass and momentum. The surface tension effect at the gas–liquid boundary was treated by the continuous surface force (CSF) scheme. The volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC) technique was used to describe the behavior of interfacial movements. Experimentally, a micro-flow visualization system was set up to observe the droplet injection progression of a Picojet® printhead. For the full ejection cycle of 200 µs, the time sequence of the droplet shape for the ejection process was predicted and compared with micro-photographed images in order to validate the computer code. A simulation with two consecutive inkjet discharges was also conducted to demonstrate the possibility of redelivering droplets nearly identical in size. Analyses on the basis of 17 numerical experiments was extended to examine the drop quality in terms of droplet topology and breakup length and time by varying the parameters of manifold length, thickness of liquid inlet, exit diameter of nozzle, ejection time and the fluid's physical properties. The droplet ejection characteristics were determined to explore whether a Picojet® printhead can be used to dispense a variety of liquids such as water, anisol, PEDOT and MEH-PPV.
TL;DR: In this paper, a numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique, which can be divided into three flow regimes: skimming flow, nappe flow and transition flow.
Abstract: Numerical simulation of stepped channel flow was conducted using turbulence models based on the VOF technique. Stepped channel flow is a complicated air-water two-phase flow with free surface, which can be divided into three flow regimes: skimming flow, nappe flow and transition flow. The characteristics of skimming flow over mild stepped channel was investigated, including friction factors, air concentration profiles velocity field, clear-water and bulked depths, static pressure, etc. Smooth channel flow was also simulated to compare the hydraulic characteristics of the stepped channel flow with the smooth one. Comparisons between the computed and the measured were made. Furthermore, comparison of the computed air concentration with Straub and Anderson's data was also performed. The Fluent 6.1 software was employed to conduct this numerical simulation work.