Volume Of Fluid Method Research Articles

Modelling green water loads on ships using coupled impulse response function and CFD solution

A 3D coupled method is used to model green water and to study numerically the influence of wavelength, wave steepness, and bow rake angle on the green water occurrence and peak pressure on a ship deck. To do that, the global motions of the vessel are obtained in the time domain using an impulse response function. The local hydrodynamic forces of green water load are computed using a commercial CFD solver together with the Volume of Fluid method. The approach is validated using in-house experimental results. Then a systematic parametric study is performed to understand the effect of several geometric and environmental parameters on green water loads. The results indicate that peak pressure due to green water increases significantly with vessel speed for all the wavelengths investigated and decreases with the increase of bow rake angle.

A contact line force model for the simulation of drop impacts on solid surfaces using volume of fluid methods

Characterizing the contact line dynamics on solid walls is often a crucial problem encountered in the simulation of complex interfacial unsteady flows, such as drop impacts on solid surfaces. In this work, a new model is proposed to reproduce the contact line dynamics in a simple but effective way, based on introducing in the momentum equation a force term proportional to the deviation of the calculated contact angle from the value predicted by a dynamic model that takes into account wettability hysteresis. The model has been implemented in a volume of fluid (VOF) method and is applied to the simulation of drop impacts leading to deposition outcomes, although it could be extended to other interface tracking methods and is also applicable to more complex drop impacts involving fingering and splashing. Numerous tests have been performed to evaluate the accuracy and robustness of the proposed model over a wide range of Reynolds and Weber numbers. The results substantially improve those obtained by imposing only the contact angle as a boundary condition at the contact line, and satisfactorily predict a variety of experimental results from the literature for very different impact and wettability conditions.

Response to the comment “Numerical simulation of steam condensation on the surface of a horizontal tube using the VOF method. A comment on the results from Li Shu and Yonglin Ju paper ‘Numerical study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain tube at Low temperatures’, International Journal of Thermal Sciences, 2022”

Response to the comment “Numerical simulation of steam condensation on the surface of a horizontal tube using the VOF method. A comment on the results from Li Shu and Yonglin Ju paper ‘Numerical study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain tube at Low temperatures’, International Journal of Thermal Sciences, 2022”

Numerical simulation of transient pipe flow with entrapped air and wet bed effects

In this study, the evolution of transient pipe flow along the wet bed is numerically investigated. In the investigation, the shear stress transport k-ω model is used and the volume of fluid method is employed to track the surface of air and water. Two key parameters in the flow as upstream head H and initial water depth h in the pipe are examined. It is found that the bottom stress is significantly affected by the two parameters. The upstream head H determines the magnitude of the shear force, and the downstream water depth in the pipe affects the stability of the shear force. The boundary layer separation and flow pattern are the essential causes of shear instability. By analyzing the simulation results, an empirical equation with the average flow velocity is obtained to estimate the overflow capacity of the pipe by just the upstream water level and the depth of the wet bed.

A study on the dynamic characteristics of surface suction vortices in an open inlet pool

The surface suction vortices in the open pump intakes were systematically investigated by using numerical and experimental methods. A 3D open inlet pool model has been applied to numerically simulate the flow pattern in the sump based on the shear stress transfer k–ω model, and the volume of fluid method was used to analyze flow fluctuations in the free surface in order to capture and identify the developing status and the evolution process of surface suction vortices as well. The results show that the surface suction vortices easily occur at large flow rates, and the suction ability of these vortices has a positive linear relationship with the flow rate, submerged depth, and the Froude constant. Moreover, it can be observed that the extended direction of the dynamic vorticity is determined by the vortex component along the Z axis (ωz), which played a major role in the stretching effect during the vortex deformation.

Application of Vortex Identification Methods in Vertical Slit Fishways

The reproduction and survival of fish are often negatively affected by the construction of dams and other hydroelectric projects, which cut off their migratory routes. Building effective fish passage facilities that allow fish to pass through dams smoothly alleviates the negative impact of hydroelectric projects on the ecological environment, thus protecting the diversity of aquatic species and preventing the extinction of indigenous fish. Vertical slit fishways are highly effective, but turbulence inside the fishway pools directly affects fish passage. In this study, the large-eddy simulation framework is used to capture the vortex characteristics in the interior of vertical slit fishway pools, and the volume of fluid method is applied to simulate the free surface. The independence of the grid is assessed by the large-eddy simulation quality index, and the simulation results are compared with experimental acoustic Doppler velocimetry data. This work characterizes the vortex flow field inside the vertical slit fishway using the Q-criterion, Omega method, and Liutex vortex identification method. The results show that the vortex structure inside the fishway pool has obvious three-dimensional characteristics and vortex structure varies within the different fishway pool chambers. The analysis and comparison of the three different vortex identification methods show that the vortex structure captured by the Liutex method is more consistent with the actual motion pattern of the fishway water flow.

Numerical simulation of steam condensation on the surface of a horizontal tube using the VOF method. A comment on the results from Li Shu and Yonglin Ju paper “Numerical Study on the Condensation Characteristics of Various refrigerants outside a horizontal Plain tube at low temperatures”, International Journal of Thermal Sciences, 2022

In the present comment, the results of recently published by Li Shu and Yonglin Ju “Numerical Study on the Condensation Characteristics of Various Refrigerants Outside a Horizontal Plain Tube at Low Temperatures” in International Journal of Thermal Sciences 2022 are discussed. It is shown that one of the conclusions of the work that “at low saturation temperatures, the periodic-averaged heat transfer coefficient in the numerical simulation is lower than that calculated with Nusselt's equation, especially at large wall subcooling”, is not supported by the results of simulation performed by the author of this comment.

Numerical modeling of liquid spills from the damaged container and collision of two rising bubbles in partially filled enclosure using modified Volume-Of-Fluid (VOF) method

In the present work, two crucial shortcomings associated with Volume-Of-Fluid (VOF) model namely: (1) spurious interface smearing arising from false-diffusion errors, and (2) non-physical velocity fluctuation across the physical discontinuities, are systematically addressed, aiming to establish a unique methodological foundation and guidelines for the enhancement of interface-capturing techniques in handling multi-fluid flows. To accomplish this objective, first, a novel third-order bounded convection scheme is derived based on the Normalized Variable Diagram and Total Variation Diminishing concepts (NVD-TVD) and is then applied for the discretization of the volume-fraction equation. To cope with the instability issue induced by pressure fluctuation, the standard version of the implicit non-iterative PISO algorithm is first modified by incorporating the third pressure-correction step into the algorithm and is then utilized for the treatment of the pressure-velocity coupling. A feasibility and applicability of the proposed modifications in dealing with violent free-surface and multi-fluid flows are demonstrated against the five different challenging benchmark cases including two-dimensional dam-break flow over the dry bed, oil spill from the damaged container, single bubble rising, merging of two rising bubbles and two-fluid Rayleigh-Taylor Instability problems. The comparison of the obtained results with previously published literatures vividly corroborates the robustness and versatility of the modified VOF model in handling multi-fluid flows involving interface coalescence and breakup events. In the last staged, three new benchmark solutions namely (1) coalescence of two consecutive bubbles inside the partially filled enclosure, (2) two-dimensional three-fluid Rayleigh-Taylor Instability, and (3) oil/water spilling from the damaged tank are analyzed using the verified VOF method, aiming to provide a high-quality validation data for CFD simulations.

Three-Dimensional Numerical Study of Dam-Break Flood Impacting Problem with VOF Method and Different Turbulence Closures

Three-Dimensional Numerical Study of Dam-Break Flood Impacting Problem with VOF Method and Different Turbulence Closures

Extending the isoAdvector Geometric VOF Method to Flows in Porous Media

We consider the interfacial flow in and around porous structures in coastal and marine engineering.* During recent years, interfacial flow through porous media has been repeatedly simulated with Computational Fluid Dynamics (CFD) based on algebraic Volume Of Fluid (VOF) methods [1] [2]. Here, we present an implementation of a porous medium interfacial flow solver based on the geometric VOF method, isoAdvector [3] [4]. In our implementation, the porous medium is treated without resolving the actual pore geometry. Rather, the porous media, pores, and rigid structure are considered a continuum and the effects of porosity on the fluid flow are modelled through source terms in the Navier-Stokes equations, including Darcy-Forchheimer forces, added mass force and accounting for the part of mesh cells that are occupied by the solid material comprising the skeleton of the porous medium. The governing equations are adopted from the formulation by Jensen et al. [1]. For the interface advection using isoAdvector, we also account for the reduced cell volume available for fluid flow and for the increase in the interface front velocity caused by a cell being partially filled with solid material. The solver is implemented in the open source CFD library OpenFOAM®. It is validated using two case setups: 1) A pure passive advection test case to compare the isolated advection algorithm against a known analytical solution and 2) a porous dam break case by Liu et al. [5] where both numerical and experimental results are available for comparison. We find good agreement with numerical and experimental results. For both cases the interface sharpness, shape conservation as well as volume conservation and boundedness are demonstrated to be very good. The solver is released as open source for the benefit of the coastal and marine CFD community (code repository https://github.com/InterFlowers/porousInterIsoFoam) and as of OpenFOAM-v2112 the new functionality is integrated in the official interIsoFoam solver. * This article is an updated version of the conference paper Missios et al. 2022 [6] presented at the Marine2021 conference.

CFD simulation of CO2 methanation through the Sabatier reaction in a shell-and-tube reactor incorporating phase change on the shell side

This paper reports a computational fluid dynamics simulation of carbon dioxide (CO2) methanation via the Sabatier process in a shell-and-tube reactor, incorporating a water phase change simulation on the shell side using the volume of fluid (VOF) method. The essential heat removal factors and their mechanisms, such as the catalyst size, bed porosity, thermal conductivity, coolant flow rate, and coolant boiling, were primarily investigated. The computational code was a newly developed in-house version of ChtMultiRegionFOAM based on OpenFOAM v2006. This code can simulate catalyst-gas heat transfer, which is called the two-temperature model. The code was extended to new methanation and phase-change models based on the VOF method. The computational code was first validated using existing experimental data. After sufficient accuracy was confirmed, several parametric studies were conducted. Catalyst heat conductivity was the most influential factor among the catalyst-related parameters. The flow rate of the oil coolant significantly affected the cooling performance. Finally, the use of boiling water significantly reduced the coolant flow rate. Moreover, the cooling performance remained unchanged until the total heat release rate from the gas exceeded the total latent heat of the water.

Numerical Analysis of Spray Characteristics With Methane and Nanoparticles Under Various Injection Velocities

Abstract Utilization of numerical simulations has been increased rapidly to test many innovative concepts in the field of advanced fuel technologies. Implementation of chemical compound's interaction is viable option by numerical tools. Hence in this current study, the numerical simulation has been performed to evaluate the effect of spray velocities on the mass fraction of various compounds. The conceptual numerical domain has been constructed with mixture of two inlets such as air and CH4 using ansys-cfd. In addition to the CH4, the nanoparticles were injected in the same inlet using the volume of fluid method. The fuel was injected at different velocities varied from 100 m/s to 175 m/s, under the intervals of 25 m/s. Here two sections of the domains are created, one for the oxidizers and another for the CH4 with nanoparticles. Throughout the entire trial runs, the nanoparticle concentration has been maintained constant. A series of the pictorial contours have been captured to understand the influence of the fuel impinging characteristics and reaction rates in the combustion chamber. The results revealed that CH4 injection enhances the vortices formation inside the combustion chamber. Furthermore, turbulence intensity inside the chamber is high which delays the reaction time and leads to the higher combustion indeed.

Numerical modelling and theoretical analysis of the acoustic attenuation in bubbly liquids

The propagations of acoustic waves in bubbly liquids have been extensively investigated through experimental and theoretical methods, a computational fluid dynamics (CFD) method was introduced to investigate the acoustic attenuation through bubbles in this study. Numerical ‘measurements’ of attenuation coefficient (α) and phase velocity (V) were conducted using a homogeneous cavitation model, which were modeled from experimental schemes and compared with the theoretical results. At extremely small bubble volume fraction (β around 10−11), new formulas of the theoretical α (αtheo) were proposed respectively for linear and transient oscillations, and a new formula of the numerical α (αnum) was proposed for transient oscillations. Results showed that αnum matched precisely with αtheo for linear, nonlinear and transient oscillations. At medium β (around 10−4), the relative difference of αnum between the VOF and present methods was less than 1.6%, while it reached 15.4% after replacing the bounded Keller-Miksis equation (KME) in the present method with the KME. However, the traditional theoretical α and V matched precisely with the predictions by the present method with the KME. Thus new theoretical α and V were proposed based on the bounded KME, and the relative differences between αtheo and αnum were less than 1%. It can be concluded that the bounded KME should be used in both numerical and theoretical predictions.

Droplet Formation, Growth and Detachment at the Interface of a Coupled Free-FLow–Porous Medium System: A New Model Development and Comparison

Coupled free-flow–porous medium systems are of great importance in various natural and industrial applications. Modeling of such systems is always challenging, especially when droplets form at the interface between the two domains. We propose a new concept to take droplet formation, growth and detachment at the interface into account. In this concept, we use pore-network modeling to describe the porous medium and the Navier–Stokes equations for the free-flow domain. New coupling conditions are developed which include droplet interactions with the free flow and the porous medium. Impacts of using different descriptions of the forces acting on the triple contact line and contact angle hysteresis on the predicted onset of the droplet detachment are examined. In addition, we compare the new approach with another model built using ANSYS Fluent based on the volume of fluid method. The results show that the new model is able to describe the droplet formation, growth and then detachment by the free flow. The proposed model provides a base for further developments to handle formation of multiple droplets at the interface between a free flow and a porous medium as well as to include the evaporation in future works.

Interfacial wave of the gas-liquid two-phase flow in unsaturated reservoir pores

Unsaturated reservoir pores exist widely in porous self-lubricating materials for the continuous consumption of lubricant. The complex gas-liquid two-phase flow behavior in the pores significantly affects the self-lubricating performance. In this paper, the two-phase flow model in unsaturated pores was established based on the Couple Level Set and Volume of Fluid method. Two kinds of porous materials with significantly different wettability, stainless steel and polytetrafluoroethylene (PTFE), were concerned. The two-phase flow behaviors were investigated to reveal the flow mechanism in the unsaturated pores. The different flow behaviors caused by the wettability of materials were quantitative characterization. Results show that, the gas rises with a convex interface in the stainless steel pore, and the bubble is generated after the contact line is pinned on the edge of the pore at 35 ms. While in the PTFE pore, the gas rises with a concave interface. And the gas profile changes from concave to convex after the contact line is pinned at 32 ms. In the two pores, the gas-liquid interface fluctuates periodically. In the hydrophilic stainless steel pore, the fluctuation amplitude decreases and finally tends to be stable with the increase of time. In the hydrophobic PTFE pore, the interface has constant fluctuation amplitude for the attraction between gas and the hole wall. The fluctuation of the gas-liquid interface has an important influence on the flow state of the lubricant film. The results help to clarify the two-phase flow mechanism within unsaturated pores, and provide guidance for the self-lubrication design of the porous materials.

Three-dimensional numerical simulation of the interaction between high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth metal

The rupture accident of the steam generator heat transfer tube of the lead-bismuth cooled fast reactor causes a high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth, and the interaction mechanism between water and liquid lead-bismuth needs to be studied clearly. In this paper, based on the volume of fluid method, the LES turbulence model and the Lee phase transition model, a three-dimensional numerical model is developed to study the multiphase flow and heat transfer mechanism of water and lead-bismuth interaction. The effects of sub-cooled water temperature, inlet pressure, and nozzle diameter on the distribution of phase state, pressure, temperature, and generated steam volume are studied in detail. The results indicate that the water jet can be divided into the jet water zone, the water-steam mixed zone, and the multiphase flow zone, respectively. Among them, the appearance of water-steam mixed zone depends on the internal boiling of the jet, and this zone tends to appear under the condition of low inlet pressure, small nozzle diameter and high sub-cooled water temperature. For multiphase flow zone, the temperature increases with sub-cooled water temperature, decreases with nozzle diameter and is almost not influenced by inlet pressure; The pressure increases with sub-cooled water temperature, inlet pressure and nozzle diameter. When nozzle diameter is large enough, however, it no longer has any effect on the temperature and pressure distribution within the jet. The volume of steam generated by water boiling is positively correlated with all three factors. Overall, the steam migrates upward through the outer side of the jet, absorbing heat and expanding during the migration process, and forming a high-temperature area at the top of the jet.

Experimental and numerical studies of solitary wave interaction with perforated caisson breakwaters

This study experimentally and numerically investigated interactions between solitary waves and the perforated caisson breakwaters. By caisson, we mean a sealed chamber filled with sand and rocks inside, and it is a common structure used for the construction of vertical breakwater. In the laboratory, the solitary waves with larger relative wave heights were well generated based on the “collapsing water column” technique and successfully acted on the perforated caisson models. Using the volume of fluid method and the k–ε model, combined with the ideal gas equation at a constant temperature, the wave transformation and vortex evolution in the vicinity of the perforated caisson breakwaters were simulated. A reasonable agreement was observed between the numerical and the experimental results. By comparing with the non-perforated caissons, the perforated caissons effectively reduced the reflected and transmitted wave heights, and the occurrence of the reflected waves was found to be delayed due to the existence of the wave chamber. Based on the numerical results, distributions of the fluid velocity and turbulence kinetic energy (TKE) near the perforated caissons were examined. The wave dissipation mechanism of perforated caisson under the solitary wave was different from that under the periodic wave. The results showed that vortices and TKE were mainly concentrated near the perforated front wall. The incident wave energy was dissipated in the generating vortices formed by fluids jetting through perforations. Additionally, variations of the wave reflection, transmission, dissipation coefficients, and wave overtopping volumes were investigated against different relative crest freeboards, relative wave chamber widths, caisson porosities, and relative wave heights under the solitary waves. Valuable results were presented for practical engineering applications.

Development of a Mathematical Model of Dispersed Phase Outflow Using Volume of Fluid Method

Development of a Mathematical Model of Dispersed Phase Outflow Using Volume of Fluid Method

Atomization of liquid pulsed jet in subsonic crossflow

Pulsed jet is an effective solution to improve fuel jet penetration depth and consequently increase the mixing efficiency of gas–liquid in conventional combustion chambers. This has the benefits of reducing pollutant emissions and diminishing the instability of fuel combustion. However, the atomization process of pulsed jets with small amplitude has still not been properly investigated. This paper studies such a process through Large Eddy Simulation and a Coupled Level Set and Volume of Fluid method. We investigate the atomization process in a liquid pulsed jet with a subsonic crossflow and the impact of the Strouhal number on atomization morphology and the behavior of the pulsed jet in general. Results show that, with a constant mass flow rate, the role of Rayleigh–Taylor instability is replaced by the periodic fluctuation of the jet velocity, which ends up dominating the primary process of atomization of the liquid transverse pulsed jet. This also improves atomization, in general, and the fragmentation of the jet. We also show that the Strouhal number significantly impacts the penetration depth of the jet, with high values increasing penetration by up to 12%.

Mapping flow-focusing microfluidic droplet formation to determine high-throughput droplet generation configurations

Droplet microfluidics enables the generation of monodisperse droplets of desired size using immiscible multiphase flows. These droplets serve as individual reactors in bio (chemical) analysis. In addition to monodispersity, high throughput is also necessary for many applications, especially in synthesizing nano- and microscale materials. Therefore, high-frequency droplet formation in the stable regimes (dripping and squeezing) is of great importance. In this work, the flow-focusing geometry is numerically investigated to determine the geometrical dimensions and flow rate ratio by which high-frequency, high mass flow rate, and monodispersed droplet formation are achievable. 3D numerical simulation has been performed with the commercial software ANSYS Fluent using the VOF method. The lowest and highest error values were 1.5% and 7% in the validation results, respectively, confirming the solver's reliability. The numerical model determined droplets' diameter and mass flow rate, and their generation frequency for a simple geometry that had been experimentally studied. The geometry, then, was changed both in dimension and junction, seeking the best performing configuration. Our results demonstrated that the highest mass flow rate and generation frequency are obtained with the flow rate ratio of 5 between the continuous and dispersed phases. Furthermore, by introducing a modified geometry using a rib, it was revealed that reducing the channel width in the simple geometry leads to much more improvement in the generation frequency and droplet diameter than using the modified geometry. Subsequently, the aspect ratio study showed that the aspect ratio 1 creates the highest production frequency in the simple geometry. Finally, taking into account all the previous findings, a relation is introduced which determines the required channel dimensions when a specific droplet diameter is of interest.