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This paper presents the computational study of air bubble evolution and disengagement in water from a single nozzle (1mmdiameter) underwater with an airflow rate of 2 mL/min using the VOF method with the LS method coupled. We have investigated the bubble evolution at different contact angles (\(50^{ \circ } \le \theta_{0} \le 110^{ \circ }\) at solid–liquid–gas interface. We examined the variation of bubble volume (V) at different contact angle and size of the bubble at the base (D) and we investigate the stages of growth of bubble termed as (1) nucleation period, (2) under critical growth, (3) critical growth, and (4) necking, during bubble rising or evolution. I saw in my study that the bubble volume depends on the wetting condition and bubble volume increases drastically as contact angle varied \(\theta_{0}\), changes from \(50^{ \circ }\) to \(110^{ \circ }\). Bubble evolution is beginning to be regulated by the hysteresis of contact angle. During the expansion stage and elongation stage of the bubble, bubble shape oscillates which was observed in my simulation. In the initial rise of bubble surface tension, capillary force is dominated and variation of viscous drag force is neglected.

In friction stir welding (FSW) process, material flow is the most important aspect which affect the mechanical properties and microstructure of the welded joints. The good plasticized material flow reduces the formation of defects in the welded joint. In the present study, a three-dimensional volume of fluid (VOF) model based on ANSYS 14.5 FE software package was developed to predict the effect of traverse speeds (i.e. 90, 132 and 180 mm/min) on material flow behaviour during FSW of low carbon steel. Stain and temperature-dependent material properties were incorporated in developed material flow model. It is observed that the tool traverse speed strongly influenced the mixing of plasticized material in FSW of low carbon steel. The velocity of material flow was reduced as the distance increases away from the rotating axis of the probe or weld zone. The velocity vector of plasticized material was different at different planes throughout the welded joint. The material in plane nearby the top surface exhibited the maximum velocity than the plane close to the bottom surface. Experiment was also carried out using tungsten carbide tool to validate the material flow model. The transient thermal profile obtained from FE analysis and experiment was agreed properly well for peak temperature with a maximum percentage error of 6.72%.

In this study, a comprehensive 2-D numerical study is conducted to investigate the heat transfer performance of phase change material (PCM)-based finned heat sink for the purpose of thermal management of electronic devices. Heat sinks are made up of aluminum and filled with paraffin wax as PCM. Various configurations of heat sink, such as plain, one fin, and two fin heat sinks are studied in this investigation. The effect of number of fins and heat flux on heat transfer performance is studied. A constant input heat flux is applied from the bottom side of the heat sink. Transient numerical simulations are performed using the Ansys fluent software. The 2-D governing equations for continuity, momentum and energy are solved by using volume of fluid (VOF) model for PCM and air composite and enthalpy porosity model is used for the phase change phenomena of PCM. The results are presented in terms of temperature variations, melt fractions and time to reach critical setpoint temperature (SPT). The results show that increasing the heat flux value increases the melting rate of PCM and increasing the number of fins increases the heat transfer performance of PCM-based heat sink.

The proper discretization of the convective terms in the Navier–Stokes equations is critical for the accurate numerical solution. The use of higher-order schemes tends to cause numerical dispersion. Hence, the present work tries to study the stabilizing effects of the lower-order scheme when blended with the higher-order schemes. This is demonstrated using the Rayleigh–Taylor (RT) instability simulated using the volume of fluid (VOF) method. The influence of blending factor on the interface topology and numerical stability is studied using normalized variable diagram (NVD) and von Neumann analysis.

The tank filling problem can be put under a broad umbrella of free surface flows. Free surface flows are characterized by phases separated by a distinct interface. In this paper, we present a discussion on tank filling problems, wherein a tank is filled by the liquid entering from two in gates. Parametric studies are performed by varying the inlet velocity and orientation of the ingate to predict the fill time, flow sequence, and track the velocities at different positions in the tank, using ANSYS Fluent. An optimal velocity was chosen to ensure there is no rapid flow movement and overflow. Providing the orientation to the ingates helped to improve the volume fill rate, though some cases showcase rapid bubble formation, and receded flow movements.

Stability analysis of complex two-phase slug flow is carried out by using OpenFOAM (CFD) open-source codes. Flow in symmetrical pipe geometry is simulated using isoAdvector (geometric algorithm) which uses VOF method to track interactions of two fluids at the interface. Grid independence is established by choosing liquid hold-up as grid sensitivity parameter. During the two-phase flow through horizontal pipes standing waves and hydraulic jumps have identical characteristics. Slugs within pipe are observed to be the sudden pressure transition or high energy zone. Due to these characteristics, a situation of hydraulic jump within and around slugs arises. Further, the mechanism of shedding and picking rate of water at slug front and alteration in length of travelling slugs are analysed.

This paper deals with the effect of Newtonian fluid’s viscosity variation on the drop formation through the computational domain. The simulation is performed on a two-dimensional domain and the “volume of fluid” method is used to investigate the impact of dispersed phase fluid’s viscosity on the dynamics of the droplet that expels from a vertical capillary tube. The computational results are validated with the experimental results. Below µ/µw ~ 100, the simulation reveals the linear variation in the dimensionless thread length Li/R. Above this ratio, an exponential increase in the dimensionless thread length is observed. The dimensionless thread length depends strongly on the fluid’s viscosity. Meanwhile, viscosity tends to damp the undulations developed by the breakup of the initial droplet.

The present work demonstrates the qualitative and quantitative comparison between high-resolution algebraic interface-capturing schemes applied to volume of fluid (VOF) method. Basic Compressive Interface-Capturing Scheme for Arbitrary Meshes (B-CICSAM), Modified Compressive Interface-Capturing Scheme for Arbitrary Meshes (M-CICSAM), Flux-Blending Interface-Capturing Scheme (FBICS) and Cubic Upwind Interpolation Based Blending Scheme (CUIBS) are compared in the present study. Comparisons are based on the L2 norm of the mass loss and topological accuracies shown by the above schemes when subjected to the known flow field causing shearing and deformation of the fluid interface. The present study also demonstrates the performance of these schemes when applied to real-life problems such as Rayleigh–Taylor instability. It is observed that FBICS is accurate and robust as compared to other methods, whereas M-CICSAM displays comparatively similar accuracy at lower Courant values but by being computationally efficient. On the other hand, it was observed that CICSAM and CUIBS display strong dependency over the Courant values.

To predict and analyze the mechanical fatigue and other damages in pipelines, caused by slug flow in petrochemical industry, large amounts of research have been assigned in understanding and prognosis of slug flow transition in straight and bend pipes. Accurate predictions of liquid hold up, pressure distribution and velocity are imperative for uninterrupted operation of the facility before actual work being carried out. With the above-mentioned motivation, this paper focuses on investigation of oil–water and oil–air two-phase flow formation in straight pipes and bend pipes and its associated pressure drop, maximum velocity and volume of fraction. Mixture model has been adopted in this computational analysis. Newtonian behavior of oil–air and oil–water interface is obtained from the model through a vertical 90° elbow with 50.2 mm pipe diameter. Four different oil velocities such as 5, 10, 15 and 20 m/s along with three air and water velocities 0.5, 1 and 2 m/s, respectively, are used in this study. Velocity distribution and pressure profile at six sections of 90° elbow are obtained and compared in order to analyze the flow pattern behavior. CFD analysis results under mixture model show a decreasing trend in pressure as mixture exits the elbow. Furthermore, it also shows a larger decrease in pressure at higher oil velocities. There is an increase in mixture velocity as the oil velocity rises as well as the water/air velocity increases. Similarly, for increase in VOF from 0.25 to 0.5, there is a significant decrease in pressure as well as increase in velocity is observed. The model can be helpful in designing pipeline and piping systems for oil extraction as well as oil refineries.

Droplet impact finds application in paint industries, spray coating, and aeration and hence becomes problem of engineering value. Velocity of impact, geometry, as well as the medium through which the droplet travels before it impacts the liquid surface plays a key role for the occurrence of droplet coalescence and droplet bouncing. In the present work attention has been given to low impact velocities ranging from 0.2 to 0.6 m/s for a droplet of diameter of 3 mm. Transition from coalescence to bouncing is observed at a velocity of 2 m/s. During the bouncing a secondary droplet forms and detaches from the parent droplet before it coalesces. Volume of fluids (VOF) method has been used to carry out the numerical simulation. VOF model is used for two or more immiscible fluids by solving a single set of momentum equation and it tracks the volume fraction of all the phases throughout the flow domain. Interface calculation has been done using Geometric Reconstruction Scheme using a Commercial software package.

Bubble and drops are of immense importance in multi-fluidic studies due to their certain characteristic behaviors. There are many studies for their homogeneous interactions like bubble–bubble or drop–drop dynamics and heterogeneous interactions such as interactions with solid particles. However, studies on the drop and bubble interactions are very limited, except for a few particularly targeted for micro-fluidics applications. Therefore, in the present study, the hydrodynamic behavior of bubble and drop during their interaction is studied using numerical simulations at a macroscopic scale. The open-source package ‘OpenFOAM’ is used to carry out the computations. The drop and bubble were allowed to achieve their terminal velocity before interactions in a vertical conduit. The sequence of intermediate phenomenon that occurred during the interaction of drop and bubble has been depicted with the help of phase fraction contours. The air bubble has penetrated through the core of the drop and resulted in the formation of an annular drop. However, both the bubble and drop have tended to regain their prior shape after the interaction. The vertical velocity of both the fluid particles is obtained with time for the entire sequence of interfacial dynamics.

Flow features at a 90-degree equal-width open-channel confluence are studied by using Computational Fluid Dynamics (CFD) software Fluent (version 17.2). Three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations supplemented with several turbulence models are solved numerically. The volume of fluid (VOF) method is used to track the water surface elevation (WSE). Three eddy viscosity turbulence models, i.e. Spalart–Allmras, Standard k-∈, SST k-ω and the Reynolds Stress Model (RSM) are chosen to model the turbulence. Simulated velocity fields and WSE match satisfactorily with the corresponding experimental results available in the literature. However, RSM shows more deviation in predicting the velocity field towards the left bank of the channel. Standard k-∈ model under-predicts the maximum width and length of the separation zone. Spalart–Allmras and SST k-ω models simulate the maximum width of the separation zone more accurately. However, these two models highly over-predict the \(L_{s}^{*} .\) RSM model over-predicts the maximum width and length of the separation zone. Simulated WSE is more accurate using standard k-∈ model than the other turbulence models.

Waxy crude oil transportation at cold subsea condition encounters a severe flow assurance problem. Occasional maintenance and emergency shutdown requirement of the crude oil pipeline may profound gelation process. The gelation of crude oil may result in pipeline blockage. In order to restart flow in a gelled pipeline, a high axial pressure gradient is applied, across the gel plug, to breakdown the gel structure. During shutdown, waxy crude gelation leads to shrinkage in the gel structure as seen in dead oil (gas de-saturated oil) and subsequently releases free gases. Free gases result in void formation and a multi-plugged gel in the industrial pipeline. The gel separated by gas pocket is termed as multi-plugged gel, which may form due to uneven earth surface, especially on sea-bed. In this work, flow restart in multi-plug gelled pipeline is investigated by solving mass and momentum balance equations together with strain-dependent rheological equation. The volume of fluid (VOF) method is utilized to distinguish bulk phases and the advection equation of volume fraction traces the motion of gel–gas interface. The time evolution of applied pressure propagation in the gelled pipeline has been compared with earlier works. It shows that the present profile exactly matches with the pressure profile in the single-phase flow before it encounters the gas pocket. The effect of multi-plug in restart operation may result in early gel degradation and flow restart. The result obtained in this work can be used to reduce the margin of safety commonly adopted due to overestimated pressure requirement.

The skin-friction drag reduction by air injection have been investigated numerically for the turbulent boundary layers first on the underside of flat horizontal surfaces and secondly on the bottom of a real LNG carrier using unstructured finite-volume CFD solver for the Reynolds averaged Navier-Stokes equations. In the present flow computations, two different multi-phase models, such as the volume of fluid (VOF) and the Eulerian multi-phase (EMP), are adopted to investigate their performances in resolving two-phase flow patterns and estimating skin-friction drag reductions. Both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated cavities, so called ‘air pockets and branches’. However, EMP model is superior to VOF model in predicting quantitatively the percentage of frictional drag reduction by air injection for the cases of both a flat-plate model and an actual ship.

The aims of this study are to determine the ideal configuration of swash bulkhead using 1/50 scaled IMO Type-C LNG tank models to lessen sloshing impact loads and to establish lowest natural frequency of each tank model. Three tank cases with vacuum ring, support ring, and holed plate placed in mid-tank, respectively, were considered and each was simulated by harmonic pitch motions of a more critical amplitude of 6o and various frequencies. The research relates to two-dimensional internal sloshing flows in three geometrically different IMO type-C LNG tank models at 70% filling condition which is 70% of tank height. The viscous two-phase model in STAR-CCM+ with the volume of fluid (VOF) interface was used to solve the sloshing flows in numerical method. While the experimental studies were carried out by other research institute in the same conditional constraints. The impact pressure loads acting on the tank walls against time induced by numerical method were compared with each other in the three tanks. In addition to this, maximum peak pressure RAO (Response amplitude operation) were plotted from numerical and experimental method for providing lowest natural frequency in each tank. The comparative studies indicate that the tank designed with swash bulkhead can reduces the sloshing impact loads, effectively and significantly.

Racing propeller in waves has long been a research hot topic but still lacks research achievements due to high difficulties both in numerical simulation and experiment. Thus more in-depth investigations are required especially those based on new numerical method, including accurate simulation of the drastic deformation of the free surface such as plunging and breaking, and accurate prediction of the serious fluctuation and deterioration of its hydrodynamic performance partially caused by the free-surface deformation. Previous numerical studies upon propeller performance in waves have focused on the fully-submerged conditions, where usually the Reynolds-Averaged Navier-Stokes (RANS) models are used to simulate the inconspicuous free surface deformation. Considering marginal air bubbles and gas-liquid mixing phenomenon around the racing propeller, instead of RANS, Large Eddy Simulation (LES) together with overset mesh method and Volume of Fluid (VOF) method is adopted in this paper for investigating the hydrodynamic performance of a racing open water propeller in regular head waves. The numerical simulation has been performed under variant submergence depths and advance coefficients, and the deformation of the free surface and its relation to propeller thrust and torque are discussed. The results of numerical simulation are validated by corresponding experiments conducted in the Circulating Water Channel Laboratory of Shanghai Jiao Tong University. The numerical errors against experimental results of time-averaged and transient thrust and torque based on LES model are reasonable and acceptable, which implies that the LES model used in this paper is suitable in dealing with propeller performance in racing conditions. As conclusions, the deterioration of time-averaged thrust and torque of racing open water propeller in regular head waves is more serious when the advance coefficient is relatively low. The fluctuation amplitude of thrust and torque time-series decreases as submergence depth increases.

Design slosh-induced loads are estimated through short-term and long-term approaches based on numerical simulations. Long duration sloshing simulations are performed using multiphase volume of fluid (VOF) based finite volume method (FVM). Slosh coupling effects are considered in determination of tank excitations. The slosh coupled ship motion solver which combines transient Green function based time-domain boundary element method (BEM) solver with viscous finite volume method (FVM) solver is employed for seakeeping analysis. Methodology used for statistical evolution of pressure is demonstrated by considering a case study. Identification of suitable probability distribution function (Weibull 3-parameter or Generalized Pareto) is found to be essential at several stages based on the fill condition and nature of impact.

The enhancement of heat transfer rate is an essential requirement for the desirable operating conditions in various fields, such as electronic cooling, nuclear reactors cooling and solar collectors. To achieve such conditions, devices such as heat pipes are increasingly drawing attention due to its ability to dissipate heat and heat management ability along with small aspect ratio. Hence, in this paper a comprehensive model of heat pipe is built in order to capture the two-phase phenomenon and thermal characteristics, along with flow visualization. The volume of fluid (VOF) model present in the FLUENT module of the computational package ANSYS is utilized in the present work, which successfully captures the evaporation–condensation phenomena, to account for two-phase flow dynamics. Moreover, to model nanofluid single-phase approach is adapted for various nanoparticles, such as Al2O3, CuO2, TiO2 and SiC and correlations available in the literature are used to estimate the effective thermophysical properties. The obtained results confirm that the utilization of nanofluids in devices such as heat pipes enhances the thermal characteristics of heat pipe, which further indicates the enhancement of heat dissipation.

The numerical modeling of two-phase flows is a challenging task especially when the density and viscosity ratios of the fluid in different phases are high. Moreover, the complexity increases in the surface tension dominant flows. Precise modeling of the surface tension force is essential in order to capture the flow physics accurately. Different methods have been developed to model such complex flows. Here, we describe the Coupled Level Set and Volume-of-Fluid method to model the two-phase flows which is very efficient in handling complex interface topology. The methodology has been tested with the real fluid flow problems and is found to be robust and accurate in capturing the two-phase flows.

The present computation study investigates multi-orifice injection with centre air core. To enhance the mixing process, high pressurized air has been injected at the centre portion of the orifice plate. Numerical simulation has been carried out to study the gaseous jet interaction and liquid jet interaction with air with toluene-air, kerosene-air and water-air as working fluids. Species transport model and Volume of Fluid (VOF) method in Multiphase model are used in the present analysis, which is capable of predicting the interface between these two different fluids each of which is having different mass densities. Initially, dimension of computational domain has been optimized by simulating jet through multi-orifice injector into mixing chamber of different dimensions. Later, grid independent study has been carried out with an optimum computational domain for five different grid sizes. Performance parameters like maximum penetration and volume fraction of liquid profile at different downstream locations has been compared in these five different cases. And one particular grid size is chosen with reasonable computational cost for the rest of analysis. Steady and transient simulations were performed to study the interaction between jet and air. Effect of centre air core on penetration length has been studied and compared. Deformation of cylindrical jet has been captured at different downstream locations and compared in steady analysis. Temporal evolution of the liquid jet forming the spray has been captured at different time-steps and compared in transient analysis.

Sloshing is a complicated fluid movement. The problem of water sloshing in closed containers has been the subject of many studies over the past few decades. This phenomenon can be described as a free surface movement of the contained fluid due to sudden excitations. When frequency of external excitation is close to natural frequency of liquid in partly filled tank or amplitude of excitation is very large, sloshing motion in the tank will be severe. It becomes a resonant phenomenon of a violent fluid motion which predominantly occurs in partially filled tanks. Thus, the impact force to the side or ceiling of tank will be significantly strong; it may destroy the structure or cause instability to it. To study this sloshing phenomenon, this paper carried out an experimental and numerical procedure in partly filled rectangular and cylindrical tanks. Simulations are done in ANSYS with water and air as the fluids. Mesh has been generated in ICEM CFD. For the multiphase modeling, volume of fluid (VOF) model is used. A forced sinusoidal motion is provided as a profile to the tank. The simulation results are validated with the experimental results for the same tank configuration. The test rig enables manipulating a tank model so that slosh waves are represented. Slosh occurrence and its effects depend on several factors like environmental conditions, geometry of the containment structure, fill level, external forces due to acceleration/deceleration of the containment body, and hydro-structural interaction.

The work presents the numerical investigation of a slot mist jet impingement cooling on an isothermal flat plate surface at three different temperatures 323, 350 and 363 K. A two-dimensional model was analyzed with mist (air and water) as working fluid. The distance from nozzle exit to the surface of the heated plate is varied from h/S = 4 and 8. The numerical analysis was carried out for jet Reynolds number Res = 2750 varying the volume fraction, vof 1–10% and size of droplet from 1 to 300 micron. Addition of mist causes significant increase of heat transfer coefficient as compared to the single-phase heat transfer coefficient. The numerical result of local heat transfer coefficient is compared with the experimental results of Gardon and Akfirat [1]. Also, the effect of heat transfer coefficient varying the distance from nozzle to plate spacing is shown. The turbulence models k − e and k − ω SST were considered for the study, and their differences are also presented.

The simplex atomizer of an annular combustion chamber of an 1100-kW class aero-derivative turboshaft engine is designed. Three-dimensional CAD model of the atomizer is made. An attempt is made to fabricate the atomizer model in 3D printing using acrylonitrile butadiene styrene and fused deposition modeling technique. The quality of the 3D printed atomizer is studied for the suitability of functional testing. It is found that the surface finish and the smallest structural features of the 3D printed model are not meeting the functional requirements. Hence, the atomizer manufactured by conventional machining is considered in numerical modeling and performance testing using Jet A fuel. The transient 2D axisymmetric flow analysis is performed by solving Navier–Stokes equations. The fuel–air interface is tracked by following the Euler–Euler approach and using the volume of fluid (VOF) surface tracking mathematical model. The velocity fields across the swirl chamber and in the near exit zone are presented. The air core formation and hollow cone spray obtained from numerical modeling are compared to previously published reports. The atomizer is tested in an atmospheric test facility to assess the quality of jet penetration and hollow cone spray formation. The observed performance characteristics are compared to the published literature and found in order. Alternative techniques for 3D printing of the atomizer and the related issues are discussed.

Based on the open source package OpenFOAM and the associated toolbox waves2Foam, the hydrodynamic performance of a dual-OWC system consisting of one on-shore and one offshore-stationary OWC devices is numerically investigated. The classical free surface capture method, volume of fluid (VOF) is utilized under the excitation of regular waves. The effects of the OWC chamber breadths, and the rear wall draught of the offshore device, dual-devices interval, on the wave energy conversion efficiency are explored thoroughly. The simulation shows that a larger chamber breadths ratio and a relative small rear wall draught of the front OWC device is more conducive to the wave energy extraction. Additional, a small devices interval is more beneficial for the overall extraction efficiency for the system than the big interval and a large interval should be avoided while designing.

Free surface flow interaction with an elastic plate is simulated by a Constraint Interpolation Profile-based Model. A finite difference method (FDM) based on the CIP method is used for solving the flow field in a fixed staggered Cartesian grid and a finite element method (FEM) is used for dealing with the structural deformation. Beside, a volume of fluid type method, the THINC/SW (Tangent of Hyperbola for Interface Capturing with Slope Weighting) method is used to capture the free surface and a Ghost-Cell Immersed Boundary Method is adopted to couple the fluid and structure interaction. To verify the model, a rolling tank sloshing with a thin elastic plate is computed. Predicted results are found to be more agreement with the experimental results than reference data. Furthermore, two other benchmark experiments are tested, including an elastic gate deformation in dam break and a hanging elastic beam in a shallow oil sloshing. The computed results agree well with published literatures. It validates the reliability of the present solver to deal with nonlinear fluid-structure interactions.

A 2-D full-coupled hydrodynamic and morphology CFD model is developed and improved based on OpenFOAM®. Two physical experiments are used to validate the model: breaking solitary wave on a sloping beach (Sumer et al. 2011); local scour beneath a pipeline under steady flow (Mao 1986). The numerical model is based on incompressible Reynolds-averaged Navier-Stokes equations and incorporated with volume of fluid (VOF) method, k-omega turbulence closure, and sediment transport model (both for bed load transport and suspended load transport). The bed evolution is tracked by dynamic mesh method. A new near wall treatment for suspended load transport, which proposed by Liu (2013), is implanted in this model. The hydrodynamic model is validated against the rigid-bed case of the breaking solitary wave experiment. The numerical results of wave surface elevation and bed shear stress agree well with those obtained from the experiments. Then the sediment transport model is validated under both solitary wave and steady flow experiments. The quantitative agreement between computed sediment bed profile and experiment results are satisfactory, despite a slight underestimation of the erosion depth in solitary wave case. The results show that the numerical model can well simulate hydrodynamic and morphology involved in coastal and ocean engineering problems, such as beach erosion and local scour under subsea pipeline.

The application of microfluidic in chemical processing, for example, the microchannel reactor has received much attention. This type of reactor can enhance the reaction efficiency due to high total interfacial area for the interaction of reactants in a multiphase reaction. The behavior of multiphase flow can create several different types of regimes such as segmented, annular, or droplet flow, depending on the flow conditions between the two immiscible liquids. The droplet flow has relatively higher total interfacial area than the annular flow. Depending on the total volumetric flow rate and volumetric ratio, the size of the microdroplet can be varied. In this study, the size of the microdroplet is investigated by varying the volumetric ratio of oil-to-methanol, O/M, and the total volumetric flowrate, QTotal. Computational fluid dynamics (CFD) method using Volume of Fluid (VOF) model is implemented to predict the size of the microdroplet produced in the microchannel reactor. In addition, the model is first validated with the experimental data which showed good agreement between numerical and experimental results. It was found that the droplet size is decreasing as the total volumetric flow rate and oil-to-methanol ratio increases, which will increase the total interfacial area. In addition, droplet regime has the highest total interfacial area, while segmented regime has the lowest total interfacial area. This finding is useful especially in designing a microreactor that controls the size of droplet and maximizes the total interfacial area, overall enhancing the reaction process.

The free navigation of Fridsma planing hull model is studied using OpenFOAM with different inflow velocities. Numerical calculation method with 6 degree of freedom motion of rigid body and unsteady two phase flow coupled is adopted for the study. The finite volume method is used to solve the Reynolds-averaged Navier-Stokes (RANS) equation and the VOF method is used to capture the free surface of air-water two phase flow. The calculation results show that the hydrodynamic lift of the planing hull increases while the wetted area decreases with increasing inflow velocity. As a result, the hydrodynamic drag is effectively controlled in this way. Furthermore, the error at low inflow velocity between the calculated drag and the corresponding experimental value is less than 10%, while the error at high inflow velocity is increased evidently, which is thought to be relevant to the complexity of the computation of unsteady 6 degree of freedom motions.

The aim of this paper to study the various transition stages of drop formation with the help of computational techniques. These regimes are being observed by varying capillary tube dimension and flow velocity. Two different drop formation mechanisms are famed: Either the drops are formed close to the capillary tip—dripping—or they break up from an extended liquid jet—jetting. Dripping faucet regime develops during the transition of the periodic regime to the jetting regime. We use glycerin as disperse phase liquid. We found that for low Weber number, the periodic dripping regimes are obtained whereas, for the high Weber number, jetting regimes are developed. We also study the variation in thread length and size of the breakoff drops and found that the variation of the thread length and the drop’s size in periodic dripping is nearly constant while these properties change in dripping faucet regime as well as in jetting regimes.

The study of surface gravity wave is very important for the safety of marine vessels and the design of coastal and offshore structures. Gravity-induced sea waves mostly show a nonlinear behaviour, but at a low wave steepness, these waves can be approximated as linear waves and superposition principles can be applied. Various wave phenomena such as standing waves, constructive and destructive interference, wave groups and generation of random waves are based on superposition principle. Random waves are generally modelled using wave spectrum, which is a representation of wave energy in the specified frequency range. Wave spectrum is broken into different wave components which are superposed to produce a random wave. In the present work, volume of fluid method is used for numerical simulation of surface gravity waves. Implicit formulation for volume fraction equation along with the bounded second order in time is used, which allows better temporal accuracy and numerical stability at larger time step size. The surface gravity wave is modelled by providing the wave profiles and velocities at upstream boundary. In the downstream, pressure outlet boundary is used for the specification of the hydrostatic pressure profile. Numerical beach zone is defined adjacent to the pressure outlet boundary to suppress the wave reflections propagating upstream. Random waves are modelled using JONSWAP spectrum. Formation of constructive and destructive interference, standing wave, wave pockets and modelling of random wave is achieved with numerical approach, and wave kinematics are validated against the analytical results.

In this work, the Volume of Fluid (VOF) [1] method is used to study bubble dynamics and collapse of bubbles on free surface in a rectangular domain with double gas inlets. The simulation is done by using open-source CFD software OpenFOAM-3.0.1 . The conservation equations for mass and momentum, which incorporates the influence of surface tension and gravity, are solved by using PIMPLE algorithm. The physical model for the simulation process is a 2D rectangular domain with a width of 50 mm and height of 100 mm. In order to study the collapsing of the bubble on the surface and free liquid surface mixing, an ullage area of 15% was considered within the domain. The numerical computation was performed with multiphase solver interFoam . Modeling of the geometry, meshing and setting the boundary conditions were done, using the OpenFOAM software. The simulation results were compared with the available literature results and found that the bubble formation and dynamics are in good agreement. The behaviors of gas bubbles emanating from two adjacent orifices at different gas velocities are studied. Mixing behavior in the bulk liquid due to bubble formation under different inlet gas velocities was also numerically investigated. The impact of surface tension and density of bulk liquid on collapsing of the bubble on the free liquid surface is investigated numerically.

Harbour resonance provides a possible way to amplify wave energy for wave energy converters (WEC) operating in regions with medium wave energy density. In the present paper, we conducted computationally a study on the amplification effect for a cylindrical caisson for different incidence angles of wave and wave numbers. Also studied here is the effect of some appendages on the caisson on wave amplifications. The open source code OpenFOAM was employed for all computations. The volume of fluid (VOF) method was employed to obtain the free surface. Features of wave patterns inside the caisson are also discussed. The results show that proper combinations of these parameters can result in significant wave amplifications in the caisson.

An efficient spray injection leads to better vaporization and better air–fuel mixing, resulting in the stable combustion and reduced emissions in the internal combustion (IC) engines. The impingement of liquid fuels on chamber wall or piston surface in IC engines is a common phenomenon, and fuel film formed during the impingement plays a critical role in engine performance and emissions, particularly under cold start conditions. Therefore, the study on the characteristics of spray impingement on the chamber wall or piston surface is necessary. However, first, due to the complexity of the practical fuel injection systems, it is difficult to attain the detailed specific information of the spray impingement from the experiments such as droplet size, mass, number, and velocity distributions in the vicinity of wall region. Second, because of the Lagrangian particle/parcel concept (a particle representing a number of droplets in simulations), the spray–wall interaction model under Eulerian–Lagrangian approach is often developed based on the individual droplet. Therefore, the individual droplet’s impingement on wall and the droplet-to-droplet collision have been extensively studied to assist in a profound perception on the spray–wall impingement. In this chapter, the encouraging experimental observations of applying optical diagnostics technology to study droplet–wall impingement are extensively discussed. Single droplet impingement on a solid surface with various conditions was examined to understand the detailed impinging dynamic process. The droplet–wall interaction outcomes, in particular focusing on the splashing criteria, were inspected, and a new correlation of deposition–splashing is developed. Post-impingement characterizations including spreading factor, height ratio, contact line velocity, and dynamic contact angle were then analyzed based on the experimental data at various test conditions. Further, the non-evaporation volume of fluid (VOF) method based on Eulerian approach was used to characterize single droplet impinging on the wall and provide a better understanding of the dynamic impact process. The simulation results of the spreading factor and height ratio matched well with the experimental results during the droplet impingement process. In addition, due to the evaporation drawing more attention during the engine combustion process, an evaporation VOF (e-VOF) sub-model was developed and applied to multi-droplet impingement on a heated surface to qualitatively and quantitatively analyze the vaporizing process as droplets impacting onto the hot surface. The information obtained from VOF simulations can be applied to improve the spray–wall interaction models in the liquid spray Eulerian–Lagrangian method.

Nowadays transporting oil in water annular flow is one of the more advanced methods of pipeline transportation, but the stability of water annulus is an important prerequisite for the good operation of the pipeline transport. Therefore, the influence of valve on the stability annular flow of high-viscosity oil and water is discussed, based on the technique of sliding mesh, and tracked the oil–water interface by VOF method, the flow characteristics of the oil and water core-annular flow (CAF) are calculated by the finite volume analysis software under different opening speed of valve and the thickness of water annulus. Finally, the simulation result has been proved by CAF experiments. The results show that the numerical calculation will help to predict the flowing rate of oil and water CAF inside the valve and the downstream pipeline. During the time that the ball valve is working, the flow course of oil and water CAF is divided into three stages, among which are the breakage of annular flow, the development of annular flow and the stabilization of annular flow. The turbulent flow after valve gradually decreased at the valve opening of 50%. The opening speed of ball valve has a great influence on the pressure and velocity of the flow field after the ball valve, and the velocity at the inlet and outlet of ball valve reaches a maximum. At the same time, the opening speed has little effect on the valve flow resistance coefficient. Only by increasing the water annulus thickness could promote oil–water CAF to be generated quickly when the valve is from the closed to fully opened. The conclusion could provide technical support for the application of oil–water core-annular flow.

A coupling method for interface computation applied in ocean ship hydrodynamics and multiphase flow simulation is presented. By utilizing the advantages of mass conservation in the VOF (Volume Of Fluid) method and of sharp interface computation (for free surface flow) in the LS (Level Set) method, a new solver that is integrated in OpenFOAM is proposed and preliminarily evaluated. Improved results are initially demonstrated through the computations of two test cases: (1) an air bubble rising in stagnant water, and (2) free surface flow surrounding an ocean cargo ship. The simulation results obtained using the new solver show good improvement, i.e., less numerical diffusion, of interface computations in comparison with those received using the original VOF method. Furthermore, the accuracy of the computed results appears to be improved as well. The new solver, after more thorough testing and calibration, can be useful for both research (e.g., computational code development and improvement, and investigation of flow physics) and application (e.g., hydro-dynamic evaluation of new ocean-ship designs).

The local interactions and fluctuations of multiphase flow properties present in upward slug/churn flow patterns through a 90\(^0\) pipe bend has been investigated. Numerical modelling technique using the Volume of Fluid method (VOF) and Reynolds Averaged Naiver-Stokes equation (RANS) was used in this study. Validation of the modelling approach was carried out using the void fraction signals from the simulation and its PDF result. These signals compared well with reported experimental results for slug and churn flow patterns. Result analysis which focused on velocity and pressure fluctuations at three different cross-sectional planes of the elbow showed a reduction in the fluctuation energy (PSD) of the velocity signal at the downstream locations compared to the upstream. Similar behaviour was seen in the pressure signal. The observation was attributed to the change in multiphase flow patterns from slug to stratified/stratified wavy flow pattern after the bend. The results from this study intend to inform enhanced description of the local fluctuations of slug geometry, density and frequency for the accurate prediction of flow induced fluctuating forces due to slug-churn turbulent flows at pipe bends.

Ocean surge may create a serious damage to coastal buildings. The surge may be generated due to high tide, storms or even from tsunami. The damage on buildings depends on shielding characteristics of the objects near the buildings. The shielding can be provided by placing small barrier or blocks in front of the considered building. It is difficult to estimate the loading on this building due to interference between waves and barrier. Wave pressure on building is numerically evaluated for the presence of macroroughness elements (small obstructions) placed in tandem arrangement in front of building. Computational Fluid Dynamics (CFD) technique is adopted for the simulation of tsunami-like solitary wave impact on macroroughness and building. Realizable k-e turbulence model is applied for turbulence modelling. Volume of Fluid (VOF) method is adopted to track the free surface movement of the flow. Wave is generated with the help of sudden discharge control at the inlet of an open channel. Wave characteristics are validated with the reported experimental results. Two types of wave height are considered in the study to evaluate the dependence between wave height and pressure on building. The results reveal that for wave height less than the building height, the placement of macroroughness is quite effective but if the wave height is more than the building height, the wave pressure reduction is not so significant.

In order to improve the performance of the numerical methodologies in studying the incompressible MHD flows, a new solver is developed and implemented into the open source Gerris code. The new Gerris-MHD solver, which is based on the Cartesian grids and the AMR technique, is able to simulate the single-phase MHD flows respectively of being bounded by electrically insulating or conducting walls with a cut-cell approach. In addition, by using the VOF method, the solver is also able to solve the multi-phase MHD flows and the discontinuities of the physical properties across the fluid-fluid interface can be handled very well. After that, the single bubble motion with or without the influence of the MF is investigated numerically, and the physical mechanisms are discussed in details.

A new method of numerical thermal-metallurgical-mechanical analysis was introduced in this paper. The CFD welding simulation is based on the mass and heat transfer analysis solving mass, momentum, and energy conservation equations along with the Volume of Fluid (VOF) method. The VOF method is employed to track the shape of the free surface. The arc and droplet heat source model with electromagnetic force and arc pressure model were used for the arc welding process. Next, the temperature history of CFD welding simulation was transferred to the FEM domain for thermal-metallurgical-mechanical analysis with CFD-FEM framework. The diffusion kinetics considered phase transformation model successfully predicted phase fraction and residual stress distribution of carbon steel weldment. By using the combination of suggested T-M-Me analysis method and CFD welding analysis, it is possible to reproduce a phenomenon closer to reality. Also, the recent CFD-based process analyses and results that can be extended to multi-physical analysis were briefly introduced. However, considerable assumptions and simplified models are different from real welding phenomena. To solve this gap and to use welding simulation as a prediction tool rather than a reproduction, many young researchers will need to challenge.

This work has been performed within the framework of the national project Tandem (2014–2017), with the aim to improve knowledge about tsunami risk on the French coasts. In this project, Principia works especially on the validation of the in-house EOLE CFD software for the simulation of tsunamis. The code solves 3D multi-phase flows on multi-blocks structured meshes coupled with a free surface tracking VOF model. Many validations have been carried out on academic test cases of wave generation, propagation, run-up and submersion. A focus has been especially done on the ‘macro-roughness’ modelling, namely the influence of buildings of significant size on the tsunami wave propagation. Two different approaches for the ‘macro-roughness’ modelling have been studied and compared, the classical projected boundary method, where only the building’s walls are discretized and its influence on the flow is taken into account by the no-slip boundary condition applied on these walls, and the immersed boundary method where a solid colour function assigns the solid/fluid ratio in each cell of the mesh. Due to their different nature, both methods present specific advantages and drawbacks (meshing set-up and topological constraint, accuracy, CPU time). Comparisons are carried out between the two macro-roughness models, and with a test case for which data issued from an experience on a city at a 1/50 scale are available.

With regarding liquefied sand as power-law non-Newtonian fluid, the method of volume of fluid (VOF) in computational fluid dynamics is adopted to conduct numerical computation about the flow push pile of post-liquefied sand. This paper analyzes the effect of consistency coefficient K and flow index n of power-law fluid on flow push pile characteristics. The results show that, this method can factually reproduce the flow deformation shape of post-liquefied sand; The displacement and stress of pile at different height both show the development law of the first increases rapidly and then gradually decreases. The variation trend of peak displacement and peak stress response of pile are significantly different along the pile. The peak displacement response of the foundation pile shows a gradually increasing distribution from the bottom to the top of the pile. The peak stress response of the foundation pile shows the rule of decreasing firstly, then increasing, and finally decreasing from bottom to top. Flow slide push pile effect of liquefied sand is simultaneously affected by the consistency coefficient and flow index. With the increase of the consistency coefficient or the flow index, the peak displacement or peak stress of the pile also increases.

Soil water retention curve (SWRC) as the constitutive relationship of hydro-mechanical coupling bridge of unsaturated soil has been experimentally investigated decades regarding impacts from dynamic effects in sandy soil and deformation in soft soil. However, due to inaccessibility of observation of microscale dynamic capillary behavior in geotechnical testing scale, most of the experimental methods can only provide the deviation between static SWRC and dynamic SWRC on drainage and imbibition. With the development of Computational Fluid Dynamic (CFD) simulation, several numerical methods so far can be utilized to investigate the soil water retention behavior in both micro- and macro-scale and upscaling between them, such as pore network model, Navier-Stokes integrated with Volume of Fluid and Level Set Method. Nevertheless, none of them provide a vision of interaction between fundamental fluid fractions in order to replicate the physical behavior of fluid tension from their mathematical expression. Compared to those CFD methods, Lattice Boltzmann Methods (LBM) is formulated on microscale for simulation of fluid dynamics. In addition to the interaction forces between fluid-fluid and fluid-solid phases, it fundamentally replicates the physical meaning of immiscible multiphase flow behavior in porous media. Therefore, LBM is selected to investigate the dynamic effect in soil water retention behavior in this study. The aim is to investigate the dynamic capillary pressure (soil suction in soil mechanics) varying with the saturation of each phase in a Representative Elementary Volume (REV) domain.

International audience; The characteristics of the flow under a sluice gate are investigated experimentally. Velocities and pressure profiles as long as the contraction coefficient are measured for various flow rates (from 30 m3/h to 50 m3/h) and used to validate numerical simulations. In this paper, 2D and 3D simulations are conducted with the open-source software OpenFOAM. Reynolds stresses model is used to model the turbulence and volume of fluids method to track the interface.

The transport with core-annular flow (CAF) is widely used in heavy oil transportation, which has low cost, less energy consumption, simple operation and other features. This transport requires two single-stage pump, one annular-flow nozzle and more connecting pipe, therefore, it is necessary to design an oil-water pump, which not only achieving the oil-water core annular flow with a single-stage pump, but also saving space for installation. A new annular-flow nozzle is introduced to assure the oil and water input, but there exists not corresponding theoretical guidance about this nozzle that is the key design issues of this oil-water pump. Combined with the TRIZ theory, the virtual modeling software is used to make a three-dimensional model of this annular-flow nozzle creatively. There are three factors are simulated by using the CFD method based on the VOF model,standard k-e turbulence model and SIMPLE algorithm, among which are the width of annular gap, the shrinking degree of the leaded pipe and water input pressure, so as to obtain the output characteristic of oil phase. The results showed that, the relatively small width of annular gap and shrinking degree could speed up the formation of the core oil phase; Progressively rising water input pressure makes a formation of CAF rapidly; Eventually the optimized model of this annular-flow nozzle is designed, which could achieve the stabilized outflow of core-annular flow. Meanwhile, the analysis would lay the foundation for future design and manufacture of the oil-water pump.

The objective of this work is to study the parametric effects on the drop formation. For this, an experimentally verified computational domain that gives an accurate result is developed in the commercial software, FLUENT version 14.0. The numerical simulation of the Navier–Stokes equation has been obtained by combining the volume of fluid model with the finite volume method. To obtain the precise results in the finite volume technique, fine meshing is developed to track the movement of droplet in the air interface. The shape of drop formation obtained through the computational method is being verified with the experimental results available in the literature. The effect of parameters, i.e., viscosity and flow rate, is investigated in detail and also validated with the previous research works. The effect of viscosity on the development of satellite drop formation is also studied. This work is quite good agreement with the experimental work.

With the development of world economy and the growing population, the shortage of water resources has become a major issue which affects survival and development of human beings. Hence, water-saving toilet is promoted and considered as the most effective way to solve this problem. In this paper, a new two-fluid approach was introduced to simulate the gas-liquid flow in the siphon pipeline. In the meantime, the VOF (Volume of Fluid) method and the RNG k-e model were adopted to analyze the relative factors such as volume fraction, pressure and velocity magnitude, and thus the diagram of curves was produced accordingly. The study also shows that the negative pressure and velocity magnitude effect the siphon action directly which is formed by high-speed flow from the jet. Furthermore, the pressure gradient caused by jet and outlet confirmed the stability of the siphon. Additionally, it has not only approved the feasibility of applying the two-fluid method to siphon pipeline, but also provided the theory foundation for improving the performance of water-saving toilet.

According to electromagnetic theory and fluid dynamics theory, the AZ31B magnesium alloy GMAW droplet transfer was simulated in the paper, by VOF model of FLUENT software to track the free interface of gas-liquid, use UDF order to add source term of momentum and energy equation. The simulation results show that when welding current is 100 A, the type of transfer belongs to globular transfer, and the type of droplet transfer of 280 A belongs to projected transfer; the critical transition current from globular transfer to projected transfer is about 220 A. With the increase of welding current, the diameter and length of droplet become small, the ratio of long axis length to the short axis length become more and more small, and the shape of droplet changes from long-oval to round. The neck part produces the maximum pressure, maximum pressure coefficient, maximum droplet velocity; the temperature gradient increases along with the axial direction; those factors will accelerate formation of the pencil tip and promote the droplet transfer.