Interface-capturing Method Research Articles

3D Numerical Investigation of Bubble Upflow Condensation Behaviors During Subcooled Flow Boiling in Mini-Channel with VOSET

In the subcooled flow boiling process, bubble condensation is an inevitable basic phenomenon. This paper studies the condensation phenomenon of the single, double vertical/horizontal saturated bubbles rising in a three-dimensional mini-rectangular channel based on the interface capture method VOSET (coupled volume-of-fluid and level set method) and the phase transition model. Bubble condensation behaviors are investigated at different initial diameters, inlet velocity distributions, subcooling temperatures, bubble gaps, and arrangement for the two-bubble condensing system especially. The effects of these parametric on bubble motion trajectory, shape evolution, volume variation, and condensation rate are presented. The numerical results indicated that the initial bubble size and liquid subcooling play an important role in influencing the shape and volume variation of condensing bubble behaviors significantly, while the inlet velocity distribution only affects bubble motion trajectory. Furthermore, the interaction and coalescence between the bubbles will affect the bubble behaviors and the condensation rate. Finally, the condensation heat transfer coefficients at the bubble surfaces for different cases simulated in this paper are presented, seemingly first in the literature.

Numerical modeling of the impact of a large scale waterfall on a solid plate

Recent hydroelectric power plant safety developments have necessitated detailed studies on dam spillway operations, especially during emergency water discharge scenarios such as overtopping. This paper presents a numerical investigation of a 10-meter high waterfall impinging on a solid plate using two-phase flow models. Our approach integrates a coupled Eulerian–Lagrangian Spray Atomization (ELSA) model with an Interface Capturing Method (ICM) to simulate the complex multiphase flow and atomization processes. Our model proficiently mapped the velocity and turbulence within the pre-impact region. To refine the accuracy of the impact pressures, we isolated this zone and implemented the Injection–Reinjection strategy, a novel numerical procedure for this type of configuration. The study reveals significant insights into the dynamic interactions of water packets with the dam structure, highlighting critical impact pressures that can influence dam stability and integrity. Our results, compared against experimental data, demonstrate the effectiveness of the modeling strategies in predicting the fluid behaviors and the subsequent pressures exerted on structural components.

On immiscibility preservation conditions of material interfaces in the generic five-equation model

Interfaces separating pure materials and mixtures tend to be severely smeared with interface-capturing methods for compressible multi-material flows, necessitating the requirement of various interface-sharpening techniques. However, these techniques have various problems related to consistency, conservation, and thermodynamic compatibility. In this work, we derive a general theoretical formulation of interface-sharpening techniques for the generic five-equation model. This theoretical formulation is not only conservative in mass, momentum, and total energy but also asymptotically compatible with the thermodynamic mixture laws of the mixture model upon which it is constructed, and is independent of various specific numerical algorithms. We further propose a general numerical method to solve this theoretical formulation. The proposed method is consistent and conservative, and it prevents spurious errors at the interfaces. Examples of one- and two-dimensional multimaterial compressible flow problems, including shocks and interfaces, are considered to verify the analysis and demonstrate the efficiency of the method.

Toward Virtual Testing of Unmanned Aerial Spraying Systems Operating in Vineyards

In recent times, the objective of reducing the environmental impact of the agricultural industry has led to the mechanization of the sector. One of the consequences of this is the everyday increasing use of Unmanned Aerial Systems (UAS) for different tasks in agriculture, such as spraying operations, mapping, or diagnostics, among others. Aerial spraying presents an inherent problem associated with the drift of small droplets caused by their entrainment in vortical structures such as tip vortices produced at the tip of rotors and wings. This problem is aggravated by other dynamic physical phenomena associated with the actual spray operation, such as liquid sloshing in the tank, GPS inaccuracies, wind gusts, and autopilot corrections, among others. This work focuses on analyzing the impact of nozzle position and liquid sloshing on droplet deposition through numerical modeling. To achieve this, the paper presents a novel six degrees of freedom numerical model of a DJI Matrice 600 equipped with a spray system. The spray is modeled using Lagrangian particles and the liquid sloshing is modeled with an interface-capturing method known as Volume of Fluid (VOF) approach. The model is tested in a spraying operation at a constant velocity of 2 m/s in a virtual vineyard. The maneuver is achieved using a PID controller that drives the angular rates of the rotors. This spraying mission simulator was used to obtain insights into optimal nozzle selection and positioning by quantifying the amount of droplet deposition.

Three-component volume of fluid method coupling with interface compression method and Eulerian–Lagrangian spray atomization surface density model for prediction of cavitating sprays

In this work, a new three phase cavitation model with Eulerian–Lagrangian Spray Atomization (ELSA) and Interface Capturing Method (ICM) coupling is presented to allow for, in a unified approach, physical insight of the surface evolution of cavitating sprays at the Sub-Grid Scale (SGS). Phase change is accounted for in the framework via mass transfer across a liquid and corresponding vapor phase. The surface density model was validated against direct numerical simulation data of an atomizing jet with a systematic variation of mesh resolutions. The sensitivity of the adjustable parameters such as the critical Weber number was also demonstrated. Then, experimental comparisons were made with a more realistic orthogonal spray geometry within a cavitating and turbulent non-cavitating system. These comparisons include both large scale visualizations and small scale SGS quantities such as the Sauter mean diameter. To our knowledge, this is the first study that presents the performance of a three phase cavitating framework with SGS ELSA-ICM coupling.

A high-order simulation method for compressible multiphase flows with condensed-phase explosive detonation in underwater explosions

This study introduces an efficient method designed for the simulation of compressible multiphase flows associated with explosive detonation, primarily in the context of underwater explosions. The proposed approach integrates three core components: the compressible Euler equations, the level-set equation, and the program burn model. Spatial terms of the compressible Euler equations undergo discretization using a fifth-order accuracy weighted essentially non-oscillation reconstruction, while the third-order total variation diminishing Runge–Kutta scheme manages the temporal terms. The level-set method ensures accurate tracking of the multiphase interface. To detail the transition from solid, non-reactive explosives to gaseous detonation products in the condensed charge's detonation reaction zone, the program burn model based on Zeldovich, von Neumann, Doering theory. The efficacy and accuracy of the incorporated program burn model and the multiphase interface capture method are employed through four benchmark tests, exhibiting excellent agreement with previously published data from alternative numerical methods or commercial software. In conclusion, applying the proposed method to four distinct engineering scenarios facilitates a comprehensive understanding of the inherent dynamics associated with detonation and shock wave generation and propagation.

Numerical investigation of the pharmacokinetics and pharmacodynamics of the chemotherapeutic drug in avascular and vascular stages of a brain tumor

One of the most commonly used approaches for treating solid tumors is the systemic delivery of chemotherapeutic drugs. However, our understanding of the factors influencing treatment efficacy through this method is still limited. This study presents a comprehensive and realistic mathematical model that incorporates the dynamics of tumor growth, capillary network extension, and drug delivery in a coupled and simultaneous manner. The model covers two stages of tumor growth: avascular and vascular. For tumor growth, a continuum model is employed using the phase field interface-capturing method. The neo-vascularization process is modeled using a hybrid discrete-continuum approach. Additionally, a multi-scale model is used to describe the pharmacokinetics of doxorubicin, considering various agents. The study investigates the effect of haptotaxis and reveals that a higher haptotaxis coefficient leads to faster tumor growth (up to 2.6 times) and a quicker progression to angiogenesis. The impact of tumor-related and drug-related parameters is also examined, including tumor size, tumor sensitivity to the drug, chemotherapy initialization, treatment cycle duration, drug affinity to cells, and drug dose. The findings indicate that chemotherapy is more effective during the angiogenesis stage when active loops have formed. Other clinical methods such as radiotherapy and surgery may be more appropriate during the avascular stage or the transition period between angiogenesis initialization and loop formation. The penetration depth of the drug decreases by approximately 50% with an increase in the drug binding rate to surface-cell receptors. As a result, high-associate-rate drugs are preferred for chemotherapy after active loops have formed, while low-associate-rate drugs are suitable for earlier stages.

Single-Bubble Rising in Shear-Thinning and Elastoviscoplastic Fluids Using a Geometric Volume of Fluid Algorithm.

The motion of air bubbles within a liquid plays a crucial role in various aspects including heat transfer and material quality. In the context of non-Newtonian fluids, such as elastoviscoplastic fluids, the presence of air bubbles significantly influences the viscosity of the liquid. This study presents the development of an interface-capturing method for multiphase viscoelastic fluid flow simulations. The proposed algorithm utilizes a geometric volume of fluid (isoAdvector) approach and incorporates a reconstructed distance function (RDF) to determine interface curvature instead of relying on volume fraction gradients. Additionally, a piecewise linear interface construction (PLIC) scheme is employed in conjunction with the RDF-based interface reconstruction for improved accuracy and robustness. The validation of the multiphase viscoelastic PLIC-RDF isoAdvector (MVP-RIA) algorithm involved simulations of the buoyancy-driven rise of a bubble in fluids with varying degrees of rheological complexity. First, the newly developed algorithm was applied to investigate the buoyancy-driven rise of a bubble in a Newtonian fluid on an unbounded domain. The results show excellent agreement with experimental and theoretical findings, capturing the bubble shape and velocity accurately. Next, the algorithm was extended to simulate the buoyancy-driven rise of a bubble in a viscoelastic shear-thinning fluid described by the Giesekus constitutive model. As the influence of normal stress surpasses surface tension, the bubble shape undergoes a transition to a prolate or teardrop shape, often exhibiting a cusp at the bubble tail. This is in contrast to the spherical, ellipsoidal, or spherical-cap shapes observed in the first case study with a bubble in a Newtonian fluid. Lastly, the algorithm was employed to study the buoyancy-driven rise of a bubble in an unbounded elastoviscoplastic medium, modeled using the Saramito-Herschel-Bulkley constitutive equation. It was observed that in very small air bubbles within the elastoviscoplastic fluid, the dominance of elasticity and capillary forces restricts the degree of bubble deformation. As the bubble volume increases, lateral stretching becomes prominent, resulting in the emergence of two tails. Ultimately, a highly elongated bubble shape with sharper tails is observed. The results show that by applying the newly developed MVP-RIA algorithm, with a tangible coarser grid compared to the algebraic VOF method, an accurate solution is achieved. This will open doors to plenty of applications such as bubble columns in reactors, oil and gas mixtures, 3D printing, polymer processing, etc.

A consistent and conservative Phase-Field method for compressible multiphase flows with shocks

A key challenge with interface-capturing methods for compressible multiphase flows is that the numerical diffusion of upwind schemes causes material interfaces to continuously diffuse over time, possibly in a non-uniform fashion. In the present study, a consistent and conservative Phase-Field model for compressible multiphase flows is derived to control mixing between different fluids at material interfaces due to numerical diffusion. The model is general as it admits an arbitrary number of phases and has no prior assumption of the formulation of the Phase-Field mechanism. Necessary physical constraints to formulate the Phase-Field mechanism are obtained by analyzing physical principles, including the second law of thermodynamics. To numerically solve the model, two consistency requirements and a general numerical strategy, called reduction consistent formulation, are proposed. The proposed approach is consistent, conservative, bound/positivity preserving for the volume fraction/mass, and prevents spurious errors at interfaces. Various two-phase compressible flow problems including shocks and interfaces are performed to verify the analysis and demonstrate the efficacy of the method. Finally, temperature equilibrium and the incompressible limit are also discussed.

A coupled Eulerian interface capturing and Lagrangian particle method for multiscale simulation

A new Eulerian–Lagrangian coupling on a staggered fluid mesh is proposed to simulate multiscale atomization. This coupling relies on a sharp interface capturing method (ICM) to transport the resolved fluid structures and a Lagrangian tracking algorithm to model the under-resolved Eulerian droplets. The Lagrangian droplets momentum is spread to the source terms of the incompressible fluid momentum equations through a spatial filtering operation, and the flow velocity around the Lagrangian droplets is corrected to account for their local flow disturbance. This allows accurate transport of Lagrangian droplets that are both smaller and larger than the fluid mesh spacing. The implementation of the algorithm for switching from and to Eulerian toward Lagrangian framework is discussed, along with criteria validating a transformation. Then the Eulerian–Lagrangian coupling is applied to several test cases from the literature, and is compared to our in-house pure ICM solver on the atomization of a liquid jet. The results show that the Eulerian–Lagrangian coupling improves the physical analysis of the atomization, and achieves more accurate results for poorly resolved droplets.

A Lattice Boltzmann Front-Tracking Interface Capturing Method based on Neural Network for Gas-Liquid Two-Phase Flow

This paper presents a new method that accurately captures the interface of gas–liquid two-phase flow using a neural network-based lattice Boltzmann front-tracking interface capturing method. The motion of a single free-falling droplet is simulated using the Front Tracking Method (FTM), enabling the acquisition of information regarding the velocity field and interface points. The velocity field and interface points from the simulations are then utilised to generate input and output datasets for training the neural network (NN) models. Subsequently, the trained Bayesian regularised Back Propagation Neural Network (BRBPNN) model is integrated into the Lattice Boltzmann method (LBM), utilising the velocity field obtained from LBM simulation as input. The predicted LBM interface exhibits remarkable agreement with the FTM interface, as evidenced by a high correlation coefficient of 0.99945 for the ordinate value of the interface point in both methods. Therefore, the proposed method achieves precise positioning of the phase interface of LBM.

Modeling and LES of high-pressure liquid injection under evaporating and non-evaporating conditions by a real fluid model and surface density approach

Numerical modeling of high-pressure liquid fuel injection remains a challenge in various applications. Indeed, experimental observations have shown that injected liquid fuel jet undergoes a continuous change of state from classical two-phase atomization and spray droplets evaporation to a dense-fluid mixing phenomenon depending on the ambient pressure, temperature, and fuel properties. Accordingly, a predictive and efficient computational fluid dynamics (CFD) model that can represent the possible coexistence of subcritical and supercritical regimes during the fuel injection event is required. The widely used Lagrangian Discrete Droplet Method (DDM) requires parameter tuning of model constants and cannot model the dense near-nozzle region. Meanwhile, the high computational cost of Interface Capturing Methods (ICM) has prohibited their application to industrial cases. Thus, another alternative is an Eulerian Diffuse Interface Model (DIM), where the unresolved interface features are modeled instead of being tracked. Accordingly, the current work proposes a fully compressible multi-component two-phase real-fluid model (RFM) with a diffused interface and closed by a thermodynamic equilibrium tabulation method based on a real-fluid equation of state. The RFM model is complemented with a postulated surface density equation for fuel atomization modeling within the Large Eddy Simulation (LES) framework. The Engine Combustion Network (ECN) Spray A injector non-evaporating and nominal evaporating conditions are used as a reference for the proposed model validation. Simulations are performed using the proposed RFM model that has been implemented in the CONVERGE CFD solver. Under the non-evaporating condition, the RFM model can capture well the fuel mass distribution in the near-nozzle field, but also the interfacial surface area. Besides, the predicted drop size from simulations falls within the experimental data range. On the other hand, under the evaporating condition, spray liquid and vapor penetrations and fuel mixture fraction distribution are also accurately predicted. The vaporization effect on the surface area density is revealed to enhance surface generation in the dense spray region while reducing the surface density in the dilute spray region. The mean droplet size is also relatively reduced under the evaporating condition in the diluted spray region. Overall, the accuracy and computationally efficiency of the proposed RFM model coupled with the surface density equation for high-pressure fuel injection modeling are confirmed, allowing its use for high pressure industrial configurations in future studies.

Evaluation of different interface-capturing methods for cryogenic two-phase flows under microgravity

The distribution of the gas–liquid interface is crucial to the accurate calculation of the flow and heat transfer of in-orbit cryogenic propellants, for which the surface tension force overtakes the gravitational force. As an essential oxidant, liquid oxygen has a lower surface tension coefficient and viscosity than most room-temperature fluids, causing a greater possibility of interface instability and breakage. Conventional numerical methods have seldom been assessed in terms of cryogenic two-phase flows under microgravity, and commercial software cannot provide a consistent platform for the assessment. In this study, a unified code based on OpenFOAM has been developed for evaluating four interface-capturing methods for two-phase flows, namely, the algebraic volume of fluid (VoF), geometric VoF, coupled level set and VoF (CLSVoF), and density-scaled CLSVoF with a balanced force (CLSVoF-DSB) methods. The results indicate that the CLSVoF-DSB method is most accurate in predicting the interface motion, because it uses the level set function to represent the gas and liquid phases. The gas–liquid interface predicted by the CLSVoF-DSB method is the most stable because it adopts the scaling Heaviside function to weaken the effects of spurious currents and increases the stability. The numerical algorithm of the algebraic VoF method is the most simple, so it has the highest efficiency. The geometric VoF uses the isoface to locate the gas–liquid interface in a grid cell, so it can obtain the thinnest interface. In applications of liquid oxygen, the CLSVoF-DSB method should be used if the overall accuracy is required.

Physics-informed neural networks for phase-field method in two-phase flow

The complex flow modeling based on machine learning is becoming a promising way to describe multiphase fluid systems. This work demonstrates how a physics-informed neural network promotes the combination of traditional governing equations and advanced interface evolution equations without intricate algorithms. We develop physics-informed neural networks for the phase-field method (PF-PINNs) in two-dimensional immiscible incompressible two-phase flow. The Cahn–Hillard equation and Navier–Stokes equations are encoded directly into the residuals of a fully connected neural network. Compared with the traditional interface-capturing method, the phase-field model has a firm physical basis because it is based on the Ginzburg–Landau theory and conserves mass and energy. It also performs well in two-phase flow at the large density ratio. However, the high-order differential nonlinear term of the Cahn–Hilliard equation poses a great challenge for obtaining numerical solutions. Thus, in this work, we adopt neural networks to tackle the challenge by solving high-order derivate terms and capture the interface adaptively. To enhance the accuracy and efficiency of PF-PINNs, we use the time-marching strategy and the forced constraint of the density and viscosity. The PF-PINNs are tested by two cases for presenting the interface-capturing ability of PINNs and evaluating the accuracy of PF-PINNs at the large density ratio (up to 1000). The shape of the interface in both cases coincides well with the reference results, and the dynamic behavior of the second case is precisely captured. We also quantify the variations in the center of mass and increasing velocity over time for validation purposes. The results show that PF-PINNs exploit the automatic differentiation without sacrificing the high accuracy of the phase-field method.

Investigation on pool-scrubbing hydrodynamics with VOF interface-capturing method

Pool scrubbing with bubble swarm generated by gas jet is an effective technique for aerosol retention at severe accidents, owing to large interfacial area and long residence time. Correct understanding of the process and thus enhancing its efficiency relies on analysis of the hydrodynamic behaviour of the gas, since it affects particle removal mechanisms directly. The objective of the present work is to explore the gas jet structure in detail by means of VOF interface-capturing method and additional techniques for tracking bubble characteristics and trajectories. The main findings are: (a) The breakup of globules in the injection zone becomes significant at high gas flow rates and has a great contribution in particle removal; (b) The increase of bubble size and velocity with the injection velocity will promote the inertial and centrifugal deposition of aerosol particles; (c) However, the coalescence probability of rising bubbles is found to increase with the gas flow rate, which may influence particle retention by re-enclosing particles from liquid film and reducing surface area; (d) Furthermore, the reduction in bubble residence time as they rise through the pool is unfavourable for particle removal. Nevertheless, liquid recirculation originated from violent interaction between the gas jet and the pool surface as well as swarm effects helps to prolong the residence of bubbles. The effect of gas flow rates on the decontamination factor is found to be associated with a variety of gas–liquid hydrodynamic phenomena. The proposed numerical approach is capable of acquiring detailed local information that is required for model development. Both the time-averaged spatial distribution of void fraction and the instantaneous size/rise velocity of individual bubbles obtained from the simulation conform to the experimental data. In the next step it will be extended to include aerosol particles.

Numerical simulations for incompressible turbulence cavitation flows with tangent of hyperbola interface capturing (THINC) scheme

In this work, we developed high-fidelity numerical solvers for turbulent cavitation flows and presented numerical simulations of cavitation and supercavitation behind an axisymmetric projectile and a conical cavitator. The proposed numerical solver is based on the homogeneous equilibrium model where the mass transfer rate between vapor and liquid is dependent on a volume of fraction (VOF) function. As a result, the numerical results of cavitation turbulent flow are heavily affected by the accuracy of the VOF evolution prediction. Thus, the proposed solver employs the Tangent of Hyperbola for INterface Capture method with Quadratic surface representation and Gaussian Quadrature scheme to accurately resolve the interfacial structures of cavitation bubbles. To effectively model the turbulent effects, the solver utilizes two approaches, respectively, i.e., the Smagorinsky model of large eddy simulation and the shear stress transport model of the Reynolds-averaged Navier–Stokes equation. The homogeneous turbulence equation systems are then discretized by the linear second-order schemes in space and time. The phase transition including both evaporation and condensation is described by the finite-rate mass transfer models such as Schnerr–Sauer and Kunz models. Numerical simulations and comparison studies are performed with the proposed solvers. Compared with previous simulation works, the current simulation results of cavity shape patterns and related hydrodynamic characteristics are in better agreement with experimental data and analytical theories, as well as reference solutions. These results validate that the proposed solver can produce high-fidelity predictions for solving the flow structures of cavitation and reentrant jet in the turbulent cavitation simulations.

Fluid–structure interaction analysis of flexible flapping wing in the Martian environment

Flapping-wing micro air vehicle (FWMAV) is an attractive idea for Mars exploration because of its high capability in a thin atmosphere. The biggest challenge for its development is an appropriate understanding of a flapping flight with flexible wings, which is significantly complicated because flexible flapping wings can undergo large-scale deformations due to the effects of wing inertia and the aerodynamic forces exerted by the surrounding atmosphere. Fluid–structure interaction (FSI) analysis is a powerful tool for accurate investigations, but it usually has a very high computational cost, making it challenging to perform necessary parametric studies for practical designing. An efficient FSI analysis method is required. On Mars, whose atmospheric density is around 1% that of Earth, aerodynamic forces have a relatively small influence on wing deformation and may even be negligible in some cases. We thus investigate the relative contributions of the inertial force of a flapping wing and the aerodynamic forces exerted by the surrounding Martian atmosphere using a two-way coupled FSI simulation, and identify the conditions under which the aerodynamic forces are negligible. Then, we develop a computationally efficient one-way coupled FSI analysis system based on the interface-capturing method to design a flexible flapping wing for Mars exploration. Under the obtained conditions, we perform parametric studies on hovering flight with flexible flapping wings in the Martian environment with multiple aerodynamic parameters, various kinematic parameters, and material properties of the wing. We conclude that an FWMAV with a payload of around 5 g can fly for more than 1 min for the maximum density of the Martian atmosphere.

Numerical Study on Compound-Slope Seawalls with Different Types of Protective Facings

Zeng, C.-S.; Zhan, J.-M., and Hu, W.-Q., 2022. Numerical study on compound-slope seawalls with different types of protective facings. Journal of Coastal Research, 38(1), 182–195. Coconut Creek (Florida), ISSN 0749-0208. The compound seawall is an important infrastructure to protect the coast effectively against tide and wave impacts. In this paper, a hybrid realizable k – ∊/laminar model and a volume of fluid interface capture method were used to study compound-slope seawalls with different types of protective facings. An analytical method was used to separate the incident wave and the reflected wave, and the numerical results for a compound-slope seawall with a hollow-block protective facing structure were verified by experimental results. The monitored wave surface, incident wave, and reflected wave data in the numerical simulation were compared with the experimental results, and the results show that the numerical model can simulate the interaction process of waves and compound-slope seawalls well. Furthermore, a series of numerical simulation studies on compound-slope seawalls under different protective facing structures with different wave heights, wave periods, water depths, and structure slopes was conducted. The results show that the hollow-block protective facings have a significant weakening effect on the reflected wave height, wave run-up, and wave force when the wave is moderate, which is important for the safety of seawall and onshore building structures.

Influence of phase-change on the collapse and rebound stages of a single spark-generated cavitation bubble

Influences of phase-change are generally ignored by current numerical models that are used to study spark-generated cavitation bubble dynamics. However, this assumption was limited to predicting bubble behaviors only at the first expansion and collapse stages. In this study, we aimed to explore the phase-change effects on the cavitation bubble dynamics over multiple cycles. A combination of a two-phase homogeneous mixture model and interface-capturing method was adopted to simulate the bubble dynamics. The full compressibility of the water and vapor phases, heat transfer, condensation, and evaporation were involved in our numerical model. Phase-change processes due to pressure changes and temperature changes were evaluated to explore the major influence phenomenon on the bubble dynamics. By comparing with experimental data, a compatible bubble shape and radius evolution under a free-field condition was obtained, particularly at the rebound and collapse stages. Disturbance secondary cavitation regions in the water field induced by rarefaction waves were observed immediately after the second rebound stage. In addition, bubble dynamic behaviors were mainly affected by the condensation phenomenon. The condensation mass transfer rate increases, becomes extremely high at the final collapse stage, and decreases during the rebound stage. Moreover, the condensation phenomenon mainly occurs at the vapor–water bubble interfaces with a thin boundary layer. The evaporation phenomenon occurred purely inside bubbles with a uniform region. Finally, we discuss the effects of phase-change by temperature changes on the cavitation bubble dynamics. In general, these effects were sufficiently small during the first two-cycle bubble oscillations.

Simulation Study on the Development Process and Phase Interface Structure of Gas-Liquid Slug Flow in a Horizontal Pipe

Here, a unified 3D numerical model of gas-liquid two-phase flow in a horizontal pipe was established using the interface capture method based on the open source software package OpenFOAM. Through numerical simulation of the natural slugging and development process of slug flow under different working conditions, the motion, phase interface structure, pressure and velocity field distributions of the liquid slug were fully developed and analyzed. The simulation results are consistent with the experiment. The results showed that during the movement of the slug head, there is a throwing phenomenon and a wave-like motion of the liquid slug. In addition, the slug tail and body area have very similar velocity profiles, and the overall velocity field distribution becomes more uniform with the development of liquid slug. Moreover, there are sudden pressure fluctuations at the head and tail of the liquid slug.