Showing papers on "Volume of fluid method published in 2005"
TL;DR: In this paper, the authors considered some aspects of water impact and green water loading by numerically investigating a dambreak problem and water entry problems, based on the Navier-Stokes equations that describe the flow of a viscous fluid.
618 citations
TL;DR: In this paper, a 3D volume of fluid (VOF) model is presented featuring an interface reconstruction technique based on piecewise linear interface representation, which can handle a large density and viscosity ratio and a large value of surface tension coefficient.
345 citations
Abstract: To study the waves and runup/rundown generated by a sliding mass, a numerical simulation model, based on the large-eddy-simulation (LES) approach, was developed. The Smagorinsky subgrid scale model was employed to provide turbulence dissipation and the volume of fluid (VOF) method was used to track the free surface and shoreline movements. A numerical algorithm for describing the motion of the sliding mass was also implemented.
To validate the numerical model, we conducted a set of large-scale experiments in a wave tank of 104m long, 3.7m wide and 4.6m deep with a plane slope (1:2) located at one end of the tank. A freely sliding wedge with two orientations and a hemisphere were used to represent landslides. Their initial positions ranged from totally aerial to fully submerged, and the slide mass was also varied over a wide range. The slides were instrumented to provide position and velocity time histories. The time-histories of water surface and the runup at a number of locations were measured.
Comparisons between the numerical results and experimental data are presented only for wedge shape slides. Very good agreement is shown for the time histories of runup and generated waves. The detailed three-dimensional complex flow patterns, free surface and shoreline deformations are further illustrated by the numerical results. The maximum runup heights are presented as a function of the initial elevation and the specific weight of the slide. The effects of the wave tank width on the maximum runup are also discussed.
246 citations
TL;DR: In this article, a mass-conserving Level-Set method to model bubbly flows is presented, which can handle high density-ratio flows with complex interface topologies, such as flows with simultaneous occurrence of bubbles and droplets.
Abstract: A mass-conserving Level-Set method to model bubbly flows is presented. The method can handle high density-ratio flows with complex interface topologies, such as flows with simultaneous occurrence of bubbles and droplets. Aspects taken into account are: a sharp front (density changes abruptly), arbitrarily shaped interfaces, surface tension, buoyancy and coalescence of droplets/bubbles. Attention is paid to mass-conservation and integrity of the interface. The proposed computational method is a Level-Set method, where a Volume-of-Fluid function is used to conserve mass when the interface is advected. The aim of the method is to combine the advantages of the Level-Set and Volume-of-Fluid methods without the disadvantages. The flow is computed with a pressure correction method with the Marker-and-Cell scheme. Interface conditions are satisfied by means of the continuous surface force methodology and the jump in the density field is maintained similar to the ghost fluid method for incompressible flows
224 citations
TL;DR: In this paper, the authors studied the process of spreading/recoiling of a falling liquid drop after collision with a flat solid surface to identify the key issues in spreading of a liquid drop on a solid surface.
Abstract: The process of spreading/recoiling of a liquid drop after collision with a flat solid surface was experimentally and computationally studied to identify the key issues in spreading of a liquid drop on a solid surface. The long-term objective of this study is to gain an insight in the phenomenon of wetting of solid particles in the trickle-bed reactors. Interaction of a falling liquid drop with a solid surface (impact, spreading, recoiling, and bouncing) was studied using a high-speed digital camera. Experimental data on dynamics of a drop impact on flat surfaces (glass and Teflon) are reported over a range of Reynolds numbers (550-2500) and Weber numbers (2-20). A computational fluid dynamics (CFD) model, based on the volume of fluid (VOF) approach, was used to simulate drop dynamics on the flat surfaces. The experimental results were compared with the CFD simulations. Simulations showed reasonably good agreement with the experimental data. A VOF-based computational model was able to capture key features of the interaction of a liquid drop with solid surfaces. The CFD simulations provide information about finer details of drop interaction with the solid surface. Information about gas-liquid and liquid-solid drag obtained from VOF simulations would be useful for CFD modeling of trickle-bed reactors.
167 citations
TL;DR: In this article, a coupled level-set and volume-of-fluid method is presented for modeling incompressible two-phase flows with surface tension, which conserves mass and captures the complicated interfaces very accurately.
Abstract: A coupled level-set and volume-of-fluid method is presented for modeling incompressible two-phase flows with surface tension. The coupled algorithm conserves mass and captures the complicated interfaces very accurately. A planar simulation of bubble growth is performed in water at near critical pressure for different degrees of superheat. The effect of superheat on the frequency of bubble formation has been analyzed. In addition, simulation of film boiling and bubble formation is performed in refrigerant R134a at near critical and far critical pressures. The effect of saturation pressure on the frequency of bubble formation has also been studied. A deviation from the periodic bubble release is observed in the case of superheat beyond 15 K in water. The effect of heat flux on the instability has also been analyzed. It is found that for water at near critical condition, a decrease in superheat from 15 to 10 K leads to oscillations with subharmonics influencing the time period of the ebullition cycle.
141 citations
TL;DR: In this paper, the authors presented an improvement of the reconstruction method proposed by Lopez et al. for two-dimensional flows, which allows tracking fluid structures thinner than the cell size by allowing the interface to be represented in each cell by two non-contiguous linear segments.
118 citations
TL;DR: In this paper, a hybrid method to simulate unsteady multiphase flows in which a sharp interface separates incompressible fluids of different density and viscosity is described, where one phase is represented by moving particles and the other phase is defined on stationary mesh.
112 citations
TL;DR: A lattice Boltzmann interface capturing method for incompressible flows that does not require the isotropic property of the fourth order lattice tensor and can generate very sharp interfaces.
Abstract: A lattice Boltzmann interface capturing method for incompressible flows is proposed in this paper. The interface is naturally captured by minimizing the free energy functional. It is easily implemented and does not require interface reconstruction as required by most of the traditional interface tracking methods such as the volume of fluid method. Moreover, the method does not require the isotropic property of the fourth order lattice tensor as do other lattice Boltzmann methods. Thus the D2Q5 (D2 means two dimensional, Q5 means five velocity model) discrete velocity model is applied in the method. The interface profile along the flat interface and coexistence curve can be given analytically. The proposed method is validated for some test cases, and compared to the volume of fluid and level set methods. Numerical results show that the present method performs very well and can generate very sharp interfaces.
78 citations
TL;DR: In this paper, a droplet impingement model is developed to simulate the transient flow dynamics during impact, spreading and solidification in a fixed Eulerian structured mesh, which is validated with experimental data from tin droplet measurements.
Abstract: Powder particles are projected from a thermal spray gun towards substrates to generate protective coatings. A clear understanding of the dynamic impingement when droplets make contact with substrates is critical for controlling and optimizing the thermal spray process. A droplet impingement model is developed to simulate the transient flow dynamics during impact, spreading and solidification. The volume of fluid surface tracking technique is employed within a fixed Eulerian structured mesh. The numerical model is validated with experimental data from tin droplet measurements. The results prove that thermal contact resistance is the key element in characterizing the substrate surface roughness for impingement modelling. It is found that spreading, solidification and air entrapment are closely related to surface roughness.
78 citations
TL;DR: In this paper, a modified two-dimensional volume of fluid (VOF) method was used to simulate liquid motion in partially saturated fracture apertures under a variety of flow conditions, such as inertial forces, viscosity, gravity acting on the fluid densities, fracture wall wetting, and the pressure drop across curved fluid-fluid interfaces due to surface tension.
Abstract: [1] Complex fluid behavior in unsaturated fracture and fracture networks, such as film flow, the migration, fragmentation, and coalescence of droplets, and rivulet flow with or without meandering or pulsation, has been widely observed in laboratory experiments. In this study, a modified two-dimensional volume of fluid (VOF) method was used to simulate liquid motion in partially saturated fracture apertures under a variety of flow conditions. This modeling approach systematically incorporates the effects of inertial forces, viscosity, gravity acting on the fluid densities, fracture wall wetting, and the pressure drop across curved fluid-fluid interfaces due to surface tension. This allows us to obtain a better understanding of the fundamental physics governing unsaturated fluid flow in fracture apertures. The VOF method is able to handle the complex dynamics of fluid-fluid interfaces and free surfaces in unsaturated fractures by using a fixed Eulerian grid. Fragmentation and coalescence of the fluids are automatically handled without resorting to complex adaptive mesh refinement or interface repairing algorithms. The wetting of fracture walls was modeled by imposing contact angles near the contact lines (contact points in two-dimensional simulations), and different contact angles were automatically chosen depending on whether the liquid interface is advancing, receding, or essentially stationary. The qualitative agreements between the numerical simulations and complex multiphase fluid dynamics reported in laboratory experiments clearly demonstrate the potential value of the VOF method for the mechanistically based modeling of immiscible liquid motion in unsaturated fracture networks.
TL;DR: In this paper, a new method for the calculation of interface pressure for front capturing methods is developed, based on the calculated pressure force at each interfacial cell face using the exact pressure due to the portion of the cell face that is occupied by each fluid.
TL;DR: In this article, the volume of fluid method implemented in a Navier-Stokes computational fluid dynamics code is employed to handle the free-surface flow of liquid sloshing.
Abstract: The present study is concerned with liquid tank sloshing at low filling level conditions. The volume of fluid method implemented in a Navier-Stokes computational fluid dynamics code is employed to handle the free-surface flow of liquid sloshing. The geometric reconstruction scheme for the interface representation is employed to ensure sharpness at the free surface. The governing equations are discretized by second order accurate schemes on unstructured grids
TL;DR: In this paper, the authors present results of a numerical investigation of the impingement process of a droplet normally onto a wall film, based on the finite volume solution of the Navier-Stokes equations, in their axisymmetric formulation, expressing the flow field of the two phases, liquid and gas, coupled by the volume of fluid method (VOF).
TL;DR: In this article, the authors derived and validated a correlation for the magnitudes 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 as observed by previous researchers, they do not decrease in magnitude with increased mesh refinement nor decreased computational time step.
Abstract: Parasitic currents are unphysical currents generated when using implementations of the Continuum Surface Force technique to model surface tension forces in multi-phase Computational Fluid Dynamics problems. We derive and validate a correlation for the magnitudes of these currents as a function of the physical and numerical parameters used in a given simulation. We find that these currents may be limited by both the inertial and viscous terms in the Navier--Stokes equations, and as observed by previous researchers, that they do not decrease in magnitude with increased mesh refinement nor decreased computational time step.
TL;DR: In this article, a numerical model representing a steep fault cutting through a horizontal seal is used to investigate patterns of fluid flow following a dilatant fault slip event, and the model is initialized with porosity, permeability and fluid pressure representing the static mechanical state of the system immediately after such an event.
Abstract: Mineralization of brittle fault zones is associated with sudden dilation, and the corresponding changes in porosity, permeability and fluid pressure, that occur during fault slip events. The resulting fluid pressure gradients cause fluid to flow into and along the fault until it is sealed. The volume of fluid that can pass through the deforming region depends on the degree of dilation, the porosity and permeability of the fault and wall rocks, and the rate of fault sealing. A numerical model representing a steep fault cutting through a horizontal seal is used to investigate patterns of fluid flow following a dilatant fault slip event. The model is initialized with porosity, permeability and fluid pressure representing the static mechanical state of the system immediately after such an event. Fault sealing is represented by a specified evolution of porosity, coupled to changes in permeability and fluid pressure, with the rate of porosity reduction being constrained by independent estimates of the rate of fault sealing by pressure solution. The general pattern of fluid flow predicted by the model is of initial flow into the fault from all directions, followed by upward flow driven by overpressure beneath the seal. The integrated fluid flux through the fault after a single failure event is insufficient to account for observed mineralization in faults; mineralization would require multiple fault slip events. Downward flow is predicted if the wall rocks below the seal are less permeable than those above. This phenomenon could at least partially explain the occurrence of uranium deposits in reactivated basement faults that cross an unconformity between relatively impermeable basement and overlying sedimentary rocks.
TL;DR: In this paper, the Eulerian-Lagrangian marker and micro cell (ELMMC) method is presented for the simulation of three-dimensional, incompressible, free surface fluid flow problems.
TL;DR: In this article, the intrusion of a fixed volume of fluid which is released from rest and then propagates horizontally at the neutral buoyancy level in a vertically stratified ambient fluid is investigated.
Abstract: The intrusion of a fixed volume of fluid which is released from rest and then propagates horizontally at the neutral buoyancy level in a vertically stratified ambient fluid is investigated. The density change is linear, in a restricted layer or over the full depth of the container, and locks of both rectangular and cylindrical shapes are considered. A closed one-layer shallow-water inviscid formulation is used to obtain solutions of the initial-value problem. Similarity solutions for the large-time developed motion and an approximate box model are also presented. The results are corroborated by numerical solutions of the full two-dimensional Navier-Stokes equations and comparisons with previously published experiments
TL;DR: In this article, a 3D Front Tracking model was used and the results were compared with simulation results obtained with a 2D Volume of Fluid model to assess the influence of the third dimension.
TL;DR: In this paper, three widely used discretization schemes for the volume of fluid method were assessed for a test case that involved general ship waves, spilling breaking waves in front of the leading edge, and bubbly free surfaces in separated regions.
Abstract: This study was concerned with the free-surface wave flow around a surface-piercing foil. The volume of fluid method implemented in a Navier–Stokes computational fluid dynamics code was employed. Three widely used discretization schemes for the volume of fluid method were assessed for a test case that involved general ship waves, spilling breaking waves in front of the leading edge, and bubbly free surfaces in separated regions. A single computational approach was selected for the comparison, and a grid-dependence study was carried out. The computational results were validated against existing experimental data, showing good agreement. The validation results suggest that all three discretization schemes perform well, but the best and most efficient results were obtained using the high-resolution interface capturing scheme.
01 Jan 2005
TL;DR: In this paper, different approaches for numerical wave tanks are introduced and used for the simulation of rogue wave sequences, which are characterized by the following key features: a) potential theory with finite element discretization (Pot/FE); b) Reynolds-Averaged Navier-Stokes Equations (RANSE) using the Volume of Fluid (VOF) method for describing the free surface.
Abstract: For the deterministic analysis of extreme structure behavior, the hydrodynamics of the exciting wave field, i. e. pressure and velocity fields, must be known. Whereas responses of structures, e. g. motions, can easily be obtained by model tests, the detailed characteristics of the exciting waves are often difficult to determine by measurements. Therefore, numerical wave tanks (NWT) promise to be a handy tool for providing detailed insight into wave hydrodynamics. In this paper different approaches for numerical wave tanks are introduced and used for the simulation of rogue wave sequences. The numerical wave tanks presented are characterized by the following key features: a) Potential theory with Finite Element discretization (Pot/FE); b) Reynolds-Averaged Navier-Stokes Equations (RANSE) using the Volume of Fluid (VOF) method for describing the free surface. For the NWT using the VOF method three different commercial RANSE codes (CFX, FLUENT, COMET) are applied to calculate wave propagation, whereas simulations based on potential theory are carried out with a wave simulation code developed at T echnical U niversity B erlin (WAVETUB). It is shown that the potential theory method allows a fast and accurate simulation of the propagation of nonbreaking waves. In contrast, the RANSE/VOF method allows the calculation of breaking waves but is much more time-consuming, and effects of numerical diffusion can not be neglected. To benefit from the advantages of both solvers, i. e. the calculation speed (Pot/FE-solver WAVETUB) and the capability of simulating breaking waves (RANSE/VOF-solver), the coupling of both simulation methods is introduced. Two different methods of coupling are presented: a) at a given position in the wave tank; b) at a given time step. WAVETUB is used to simulate the propagation of the wave train from the start towards the coupling position (case A) or until wave breaking is encountered (case B). Subsequently, the velocity field and the contour of the free surface is handed over as boundary (case A) or initial values (case B) to the RANSE/VOF-solver and the simulation process is continued. To validate these approaches, different types of model seas for investigating wave/structure interactions are generated in a physical wave tank and compared to the numerical simulations.Copyright © 2005 by ASME
TL;DR: In this paper, a three-dimensional model of droplet impact and solidification has been modified to include the effects of density variation during phase change, and the model is validated against the Stefan and planar solidification problems.
Abstract: A three-dimensional model of droplet impact and solidification has been modified to include the effects of density variation during phase change. The governing equations for conservation of mass, momentum, and energy, and a volume-of-fluid (VOF) equation are derived by assuming different but constant solid and liquid densities. The equations are solved numerically using a control-volume approach. The model is validated against the Stefan and planar solidification problems. It is then applied to simulate the effects of density variation during solidification of molten tin in a mold and also of an impacting tin droplet on a substrate.
TL;DR: In this article, the effect of interfacial forces with constant surface tension on the mobility of a water droplet under the influence of the oxidant fluid in a PEM fuel cell is studied computationally.
Abstract: The mobility of a water droplet under the influence of the oxidant fluid in a channel of a PEM fuel cell is studied computationally. The performance of a PEM fuel cell is highly dependent on the oxygen transport rate, which in turn is strongly affected by the presence of liquid water. Excessive liquid water in the cathode causes cathode flooding which is generally known to be the primary reason for low cell performance. The exerted forces by the oxidant flow help to remove most of the liquid water that is entrapped in the porous electrode, hence minimizing electrode flooding. In this study the effects of liquid water and surrounding fluid properties on the mobility of the water droplets is addressed. The numerical solution is based on solving Navier–Stokes equations for Newtonian liquids. The study includes the effect of interfacial forces with constant surface tension. The volume-of-fluid method is used to keep track of the deformation of free surfaces. A comprehensive set of simulations is conducted covering a wide range of density ratios, viscosity ratios, Capillary numbers, Ca, and Reynolds numbers, Re. Deformation of water droplets and their motion is characterized based on the maximum distance between the droplet surface and the channel wall. This characteristic length has been used to compare systems with different droplet and surrounding fluid properties. Among the parameters affecting the mobility of water droplets in a PEM fuel cell, the surface tension is found to have the most important effect. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, a numerical study of heat transfer and fluid flow characteristics during the impact and solidification of liquid droplets on a cold substrate was performed by adopting a fixed grid (Eulerian) approach with a single set of mass, momentum and energy conservation equations.
TL;DR: In this article, a model describing the hydrodynamics and heat transfer due to evaporation of the gravity-and shear-driven undisturbed liquid film on structured surfaces was developed.
Abstract: One of the most important tasks in development of modern gas turbine combustors is the reduction of NOx emissions. An effective way to reduce the NOx emission is using the lean premixed prevaporization (LPP) concept. An important phenomenon taking place in LPP chambers is the evaporation of thin fuel films. To increase the fuel evaporation rate, the use of microstructured walls has been suggested. The wall microstructures make use of the capillary forces to evenly distribute the liquid fuel over the wall, so that the appearance of uncontrolled dry patches can be avoided. Moreover, the wall structures promote the thin film evaporation characterized by ultra-high evaporation rates. An experimental setup was built for the investigation of thin liquid films falling down on the outer surface of vertical tubes with either a smooth or structured surface. In the first testing phase water is used, fuel like liquids will be used later on. The thin film can be heated from both sides, by hot oil flowing inside the tube, and by hot compressed air flowing in co-current direction to the thin film. The film is partly evaporated along the flow. Results for the wavy film structure at different Reynolds numbers are reported. For theoretical investigations a model describing the hydrodynamics and heat transfer due to evaporation of the gravity- and shear-driven undisturbed liquid film on structured surfaces was developed. For low Reynolds numbers or low liquid mass fluxes the wall surface is only partly covered with liquid and the heat transfer is shown to be governed by the evaporation of the ultra-thin film in the vicinity of the three-phase contact line. A numerical model for the solution of a two-dimensional free-surface flow of a liquid film over a structured wall was also developed. The Navier–Stokes equations are solved using the Volume of Fluid (VOF) technique. The energy equation is included in the model. The model is verified by comparison with data from the literature showing favorable agreement. In particular, the proposed model predicts the formation of capillary waves observed in the experiments. The model is used to investigate the flow of liquid on a structured wall. This calculation is the first step towards the modeling of a three-dimensional wavy flow of a gravity- and shear-driven film along a wall with longitudinal grooves. It is found that due to the Marangoni effect, a circulating flow arises within the cavity, thereby leading to an enhancement in the evaporation rate.
TL;DR: In this paper, a detailed analysis of the liquid film characteristics and the accompanying heat transfer of a free surface controlled liquid impinging jet onto a rotating disk is presented, where the computations were run on a two-dimensional axi-symmetric Eulerian mesh while the free surface was calculated with the volume of fluid method.
01 Jan 2005
TL;DR: Comparison with previously published results for test problems involving severe deformation of the materials (such as vortex-in-a-box problem) show that this procedure produces more accurate results and reduces the “numerical surface tension” typically seen in VOF methods.
Abstract: An advanced Volume-of-Fluid or VOF procedure for locally conservative reconstruction of multi-material interfaces based on volume fraction information in cells of an unstructured mesh is presented in this paper. The procedure employs improved neighbor definitions and topological consistency checks of the interface for computing a more accurate interface approximation. Comparison with previously published results for test problems involving severe deformation of the materials (such as vortex-in-a-box problem) show that this procedure produces more accurate results and reduces the “numerical surface tension” typically seen in VOF methods.
TL;DR: A fixed-mesh method for general moving objects in fluid flow was developed and implemented into the commercial CFD software FLOW-3D and a good agreement is achieved between computational and experimental results in an application to a valve problem.
Abstract: In this work, a fixed-mesh method for general moving objects in fluid flow was developed and implemented into the commercial CFD software FLOW-3D. A general moving object is a rigid body with any type of six-degrees-of-freedom, fixed-point and fixed-axis motion which can be either user-prescribed or dynamically coupled with fluid flow. The method allows multiple general moving objects, and each of them can possess any different type of motion. Area and volume fractions to represent the objects in the fixed-grid are calculated at every time step to describe time-variation of object locations and orientations. Continuity and momentum equations for fluid are modified to account for the effects of object motion on fluid flow. A good agreement is achieved between computational and experimental results in an application to a valve problem.
Patent•
31 Oct 2005TL;DR: In this paper, a vorticity concentration-producing component is disposed on a pressure side of the solid body and a synthetic jet actuator is operated to periodically change the volume within the internal chamber such that a series of fluid vortices is generated and projected in the external environment out from the opening of the jet housing.
Abstract: Systems and methods for modifying fluid flowing over solid bodies are provided. A representative system incorporates a vorticity concentration-producing component and a synthetic jet actuator. The vorticity concentration-producing component is disposed on a pressure side of the solid body. The fluid flowing over the solid body remains attached to a surface of the solid body in a vicinity of the vorticity concentration-producing component. The synthetic jet actuator includes a jet housing that incorporates an internal chamber with a volume of fluid and an opening in the jet housing connecting the internal chamber to an external environment having the fluid. The synthetic jet actuator is operative to periodically change the volume within the internal chamber such that a synthetic jet stream comprising a series of fluid vortices is generated and projected in the external environment out from the opening of the jet housing resulting in a reduction in pressure drag of the solid body compared to the pressure drag exhibited by the solid body without operation of the synthetic jet actuator.
TL;DR: Nonzero divergence in the mass equation of Navier–Stokes equations is introduced to simulate water penetration from on-surface flow into substrate material and the volume of fluid method is adopted to track the free surface.
Abstract: Although many papers have been published in the field of fluid simulation, little attention has been paid to on-surface flow involving wetting and stain transportation as well as erosion and deposition phenomena. In this paper, we introduce nonzero divergence in the mass equation of Navier–Stokes equations to simulate water penetration from on-surface flow into substrate material. Also, the volume of fluid method is adopted to track the free surface. With a computation of the actual amount of absorbed water we render the wetting effects with fully dry and fully wet texture images simultaneously. Using our model, the on-surface flow that accompanies water absorption can be simulated realistically in real time with OpenGL preview rendering. Experimental results illustrate that our model can be widely applied to solve various problems related to on-surface flow.