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Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition

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A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: 31 July 2026 | Viewed by 10506

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Special Issue Editors

Dr. Van-Tu Nguyen

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Guest Editor

School of Mechanical Engineering, Pusan National University, Busan 46241, Republic of Korea
Interests: computational fluid dynamics; numerical methods; numerical algorithms; numerical programming; fluid mechanics; multiphase flows, shock capturing; free surface flows; water entry/water exit; cavitation; bubble dynamics; cavitation erosion; heat and mass transfer; gas dynamics and industrial gas flows; supercavitation; high-speed subsonic-supersonic flows
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Dr. Hemant J. Sagar

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Guest Editor

Dr.-Ing., Department of Hydro and Renewable Energy, Indian Institute of Technology (IIT), Roorkee 247667, Uttarakhand, India
Interests: multiphase flows; experimental fluid dynamics (EFD); numerical methods (CFD and FEM); bubble dynamics; cavitation bubble dynamics; cavitation; cavitation-erosion; cavitation-silt erosion; laser induced cavitation bubbles; hydrodynamics supercavitation; offshore wind turbines (floating and fixed); fluid-structure interaction; erosion resistant coatings; acoustics; cavitation based biomedical technology; quantitative analysis of flow; hydrodynamics

Special Issue Information

Dear Colleagues,

Two-phase flows (e.g., gas–gas, gas–liquid, liquid–liquid) are found in many natural phenomena, engineering, and industrial applications. The nonlinear motions of the interface between two phases (two fluids) and its deformations and breaks, phase change, heat transfer, turbulence, shockwaves, and violent interaction with devices/systems become very complicated, both in terms of developing experimental techniques for their measurement and for numerical modeling for the analysis of these two-phase flows. However, the significance of these topics has motivated the recent advances in thermodynamics, experimental measurements, and numerical modeling; these advances have demonstrated and provided a solid understanding of fundamental and physical insights into the two-phase flows in many fields of engineering and industry. These advances are in parallel with highly advanced technologies of high-speed cameras and lighting as well as high-speed computing sources, and therefore resolve the underlying physical processes satisfactorily and support the development of new technologies/treatment protocols.

This Special Issue aims to provide researchers and scientists with the opportunity to present and discuss their original works on new numerical modeling, simulations, and experimental representation of engineering and industrial systems or any other two-phase systems from microscale to larger-scale problems. Submissions of papers related to two-phase flows that not only address fundamental science but also engineering applications are highly encouraged.

Dr. Van-Tu Nguyen
Dr. Hemant J. Sagar
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Methodologies:

Two-phase flow measurement; visualization techniques
Numerical modeling; simulation of two-phase flows
Modeling phase change/boiling
Treatments of interface discontinuity and shockwave

Basic research:

Bubble/droplet dynamics
Surface tension/Capillary effects
Natural and ventilated Cavitation/ Supercavitation
Sheet, cloud, and/or tip vortex cavitation
Boiling and condensation in benchmark problems
Free surface flows
Water entry and exit flows
Fluid-Structure-Interaction
Slamming and Sloshing

Advances in Applications:

The potential risks of failure of levees, dams, and reservoirs
Breaking waves; overtop- ping of coastal structures
Moving ships; interaction of extreme waves; and green water on decks
Spray cooling and two-phase heat transfer
Hydrodynamic cavitation and dynamic bubble processes
Enhancement of critical heat flux

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Related Special Issue

Numerical Modeling and Experimental Studies of Two-Phase Flows in Fluids (13 articles)

Published Papers (9 papers)

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Research

19 pages, 3660 KB

Open AccessArticle

Spatiotemporal Analysis of Transient Liquid Film Shape

by Gašper Vidic, Saša Bajt and Božidar Šarler

Fluids 2026, 11(3), 67; https://doi.org/10.3390/fluids11030067 - 3 Mar 2026

Viewed by 330

Abstract

Precise control of thin liquid film deposition is crucial in applications where film stability and internal liquid flow significantly impact the dry film shape or the efficiency of sample or drug delivery. No prior work has automated the extraction and measurement uncertainty quantification of film geometric parameters from dual-view optical visualization with minimal user input. We present Python-based software that extracts time-resolved film thickness, width, and the positions of three contact lines from visual data using computer vision. The utility of such analysis is demonstrated by depositing 30% glycerol on a flexible tape through a circular nozzle orifice. The nozzle is positioned at a distance of h = 0.3 mm from the tape at an angle of attack α = 45°, with deposition controlled at a volume flow rate

\dot{V}

= 30 μL min⁻¹ and tape velocity v = 1.0 mm s⁻¹. Expanded measurement uncertainties are 21 μm, 22 μm, and 53 μm for the upstream static, downstream static, and upstream dynamic contact line positions, respectively, with maximum relative uncertainties of 10.3% and 8.2% for film thickness and width. Static contact line oscillations remain within measurement uncertainty, whereas the upstream dynamic contact line exhibits resolvable oscillations. This dual-view framework provides high-resolution insights into liquid film dynamics, which is crucial for comprehensive control of liquid film deposition. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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16 pages, 3883 KB

Open AccessArticle

Effects of Nozzle Geometry on Fine Bubble Generation and Surface Cleaning Performance

by Xin Jiang, Ryota Matoyama, Yumiko Otobe, Masaki Shimazu and Satoru Ogahara

Fluids 2026, 11(3), 63; https://doi.org/10.3390/fluids11030063 - 27 Feb 2026

Viewed by 309

Abstract

Fine bubbles have attracted attention in recent years due to their promising characteristics and extensive applications. One type of fine bubble generator, the Venturi tube, utilizes a sudden change in pressure inside the tube and is widely used due to its simple structure, high generation efficiency, and low power consumption. The volume of bubbles generated (generation yield) and their average diameter are key parameters in evaluating the performance of a Venturi tube generator, which depends on both the flow conditions and the geometric configuration of the generator. In this study, an oral irrigator incorporating fine bubble technology was developed, with a Venturi tube embedded in the irrigator for fine bubble generation. We designed Venturi tubes with various geometric configurations under different flow conditions to enhance fine bubble generation performance and cleaning efficiency through both experiments and numerical simulations. The results indicate that the generation performance and cleaning performance of fine bubbles are strongly influenced by the geometric parameters of the Venturi tube. Among the tested configurations, the Venturi tube with a divergent angle of 5° and a divergent length of 30 mm demonstrated the best performance. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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26 pages, 15207 KB

Open AccessArticle

Solid–Liquid Flow Analysis Using Simultaneous Two-Phase PIV in a Stirred Tank Bioreactor

by Mohamad Madani, Angélique Delafosse, Sébastien Calvo and Dominique Toye

Fluids 2026, 11(1), 17; https://doi.org/10.3390/fluids11010017 - 8 Jan 2026

Viewed by 745

Abstract

Solid–liquid stirred tanks are widely used in multiphase processes, including bioreactors for mesenchymal stem cell (MSC) culture, yet simultaneous experimental data for both dispersed and carrier phases remain limited. Here, a refractive index-matched (RIM) suspension of PMMA microparticles ( [...] Read more.

d_{p} = 168 μm

ρ_{p} / ρ_{l} \approx 0.96

) in an NH₄SCN solution is studied at an intermediate Reynolds number (

R e \approx 5000

), low Stokes number (

S t = 0.078

), and particle volume fractions

0.1 \leq α_{p} \leq 0.5

v%. This system was previously established and studied for the effect of addition of particles on the carrier phase. In this work, a dual-camera PIV set-up provides simultaneous velocity fields of the liquid and particle phases in a stirred tank equipped with a three-blade down-pumping HTPGD impeller. The liquid mean flow and circulation loop remained essentially unchanged with particle loading, whereas particle mean velocities were lower than single-phase and liquid-phase values in the impeller discharge. Turbulence levels diverged between phases: liquid-phase turbulent kinetic energy (TKE) in the impeller region increased modestly with

α_{p}

, while solid-phase TKE was attenuated. Slip velocity maps showed that particles lagged the fluid in the impeller jet and deviated faster from the wall in the upward flow, with slip magnitudes increasing with

α_{p}

. An approximate axial force balance indicated that drag dominates over lift in the impeller and wall regions, while the balance is approximately satisfied in the tank bulk, providing an experimental benchmark for refining drag and lift models in this class of stirred tanks. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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35 pages, 10685 KB

Open AccessArticle

Heat Transfer Prediction for Internal Flow Condensation in Inclined Tubes

by Mateus Henrique Corrêa, Victor Gouveia Ferrares, Alexandre Garcia Costa, Matheus Medeiros Donatoni, Maurício Mani Marinheiro, Daniel Borba Marchetto and Cristiano Bigonha Tibiriçá

Fluids 2025, 10(12), 326; https://doi.org/10.3390/fluids10120326 - 9 Dec 2025

Viewed by 572

Abstract

This study investigates the heat transfer coefficient (HTC) during flow condensation inside smooth inclined tubes, analyzing the combined effects of flow orientation, fluid properties and flow characteristics on the thermal performance. The literature review indicates that the channel inclination effect on the HTC remains insufficiently understood, highlighting the need for further investigation. Thus, a comprehensive experimental database comprising 4944 data points was compiled from 24 studies, including all flow directions, from upward, to horizontal, downward, and intermediate orientations. The study reveals that the influence of flow inclination on the HTC can be ruled by a criterion based on the liquid film thickness Froude number,

{Fr}_{δ}

. At

{Fr}_{δ}

> 4.75, the effect of flow inclination becomes negligible, while under

{Fr}_{δ}

< 4.75, the inclination can have a considerable effect on the HTC. The experimental data show that at low Froude numbers, upward flow typically exhibits higher HTC compared to downward flow, attributed to enhanced interfacial turbulence caused by opposing gravitational and shear forces. In contrast, under vertical downward flow, the annular pattern is more prominent, with reduced interfacial disturbances, limiting HTC performance. The compiled experimental database for inclined channels was compared against an update list of prediction methods, including seven correlations incorporating the inclination angle as an input parameter. Additionally, a new simple correction factor including the effect of inclined tubes was proposed based on the flow inclination angle and on the liquid film thickness Froude number. The proposed correction factor improved the prediction of well-ranked correlations in the literature by over 20% for stratified flow pattern conditions and by more than 5% for low Froude number values. These findings present new insights into how tube inclination can affect heat transfer in a two-phase flow. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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25 pages, 3412 KB

Open AccessArticle

Experimental Investigation of the Effects of Blocky Cuttings Transport on Drag and Drive Torque in Horizontal Wells

by Ye Chen, Wenzhe Li, Xudong Wang, Jianhua Guo, Pengcheng Wu, Zhaoliang Yang and Haonan Yang

Fluids 2025, 10(9), 219; https://doi.org/10.3390/fluids10090219 - 22 Aug 2025

Viewed by 1231

Abstract

The deposition of large-sized cuttings (or blocky cuttings) is a critical risk factor for stuck pipe incidents during the drilling of deep and extended-reach wells. This risk is particularly pronounced in well sections with long borehole trajectories and low drilling fluid return velocities, where it poses a substantial threat to wellbore cleanliness and the safe operation of the drill string. This study utilizes a self-developed visual experimental platform to simulate the deposition evolution of large-sized cuttings (20–40 mm in diameter) in the annulus under various wellbore inclinations and drilling fluid parameters. The stable height, lateral distribution characteristics, and response patterns of the resulting cuttings bed under different conditions were quantitatively characterized. Building upon this, a theoretical contact friction model between the drill string and the cuttings bed was employed to investigate how the bed height influences hook load during tripping and rotary torque during top drive operation. A mapping relationship was established between cuttings bed structural parameters and the resulting additional loads and torques. Results reveal significant interactive effects among drilling fluid velocity, fluid density, drill pipe rotation speed, and wellbore inclination on both cuttings bed development and associated drill string loads. Strong correlations were identified among these parameters. Based on these findings, a stuck pipe early-warning indicator system is proposed using frictional load thresholds, with clearly defined safety limits for cuttings bed height. Recommendations for optimizing cuttings transport parameters through coordinated control of fluid velocity, density, and rotary speed are also provided, offering theoretical support and engineering guidance for borehole cleaning strategies and stuck pipe risk prediction in large cuttings scenarios. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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16 pages, 2361 KB

Open AccessArticle

Numerical Investigation of a Gas Bubble in Complex Geometries for Industrial Process Equipment Design

by Daniel B. V. Santos, Antônio E. M. Santos, Enio P. Bandarra Filho and Gustavo R. Anjos

Fluids 2025, 10(7), 172; https://doi.org/10.3390/fluids10070172 - 30 Jun 2025

Viewed by 719

Abstract

This study investigates three-dimensional two-phase flows in complex geometries found in industrial process equipment design using finite-element numerical simulations. The governing equations are formulated in three-dimensional Cartesian coordinates and solved on unstructured meshes employing the Taylor–Hood “Mini” element, selected for its numerical stability and convergence properties. The convective term in the momentum equation is discretized using a first-order semi-Lagrangian scheme. The two fluid phases are separated by an interface mesh composed of triangular surface elements, which is independent of the primary volumetric fluid mesh. Surface tension effects are incorporated as a source term using the continuum surface force (CSF) model, with the curvature computed via the Laplace–Beltrami operator. At each time step, the positions of the interface mesh nodes are updated according to the local fluid velocity field. The results show that the methodology is stable and can be used to accurately model two-phase flows in complex geometries found in several engineering solutions. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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13 pages, 987 KB

Open AccessArticle

Concentration Monitoring of Highly-Diluted Crude Oil-In-Water Emulsions by Ultrasonic Backscattering Sensors

by Carlos A. B. Reyna, Ediguer E. Franco, Santiago Laín, Timoteo F. de Oliveira, Marcos S. G. Tsuzuki and Flávio Buiochi

Fluids 2025, 10(5), 108; https://doi.org/10.3390/fluids10050108 - 25 Apr 2025

Viewed by 1247

Abstract

This work deals with the feasibility of ultrasonic monitoring of the crude oil content in highly diluted crude oil-in-water emulsions, common mixtures obtained in the coalescence process of the petroleum industry. The measurement principle is the determination of the time of flight using the reflected pulses from a set of scatterers located in the near field of commercial transducers of 5 and 10 MHz. Dispersers consist of two rows of metal wires tensioned in front of the transducer using a specially designed mechanical part. The resulting assembly is a probe that can be introduced into a tank or pipe to perform the measurement. Experiments with crude oil-in-water emulsions with concentrations from 10 to 2000 ppm (parts per million) at a temperature of 20 °C were carried out. The results show that the small changes in the propagation velocity resulting from changes in concentration and temperature can be detected by the developed ultrasonic sensor. This opens up the possibility of determining the oil content in the emulsion by means of a calibration approach. The main motivation is the development of techniques for real-time monitoring of crude oil content in the wastewater produced in the petroleum industry. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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20 pages, 4126 KB

Open AccessArticle

Evolution of Wind-Generated Shallow-Water Waves in the Framework of a Modified Kadomtsev–Petviashvili Equation

by Montri Maleewong and Roger Grimshaw

Fluids 2025, 10(3), 61; https://doi.org/10.3390/fluids10030061 - 27 Feb 2025

Cited by 3 | Viewed by 929

Abstract

In a recent paper, denoted by MG24 in this text, we used a modified Korteweg–de Vries (KdV) equation to describe the evolution of wind-driven water wave packets in shallow water. The modifications were several forcing/friction terms describing wave growth due to critical-level instability in the air, wave decay due to laminar friction in the water at the air–water interface, wave growth due to turbulent wave stress in the air near the interface, and wave decay due to a turbulent bottom boundary layer. The outcome was a KdV–Burgers type of equation that can be a stable or unstable model depending on the forcing/friction parameters. In most cases that we examined, many solitary waves are generated, suggesting the formation of a soliton gas. In this paper, we extend that model in the horizontal direction transverse to the wind forcing to produce a similarly modified Kadomtsev–Petviashvili equation (KPII for water waves in the absence of surface tension). A modulation theory is described for the cnoidal and solitary wave solutions of the unforced KP equation, focusing on the forcing/friction terms and the transverse dependence. Then, using similar initial conditions to those used in MG24, that is a sinusoidal wave with a slowly varying envelope, but supplemented here with a transverse sinusoidal term, we find through numerical simulations that the radiation field upstream is enhanced, but that a soliton gas still emerges downstream as in MG24. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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19 pages, 5644 KB

Open AccessArticle

Simulation of Transpiration Cooling with Phase Change Process in Porous Media

by Aroua Ghedira, Zied Lataoui, Adel M. Benselama, Yves Bertin and Abdelmajid Jemni

Fluids 2025, 10(2), 52; https://doi.org/10.3390/fluids10020052 - 19 Feb 2025

Cited by 3 | Viewed by 2948

Abstract

Phase change modeling in porous media is among the important challenges in many essential engineering problems, including thermal management, energy conservation or recovery, and heat transfer. One particularly efficient method of dissipating heat in a porous material is transpiration cooling with phase change. It is one of the most innovative cooling methods available for removing excessive heat flux from engine components such as combustors or gas turbine blades. There is, however, a lack of in-depth understanding of the interconnected mechanisms involved in such an application. In this work, an innovative numerical solver built on the OpenFOAM environment is constructed in order to explore the phase change process in a porous medium. The volume-of-fluid method and the Lee phase change model are applied in this numerical approach. The effects of coolant flow mass rate, heat flux, and porosity of porous structure on temperature and saturation distribution are investigated and discussed. The effects of both the external heat flux and the coolant mass flow rate under fixed porosity are also studied. The phase change is then delayed in the porous matrix when the amount of the injected coolant is increased. It reduces the area of two-phase and vapor regions. Also, a considerable rise in the upper surface temperature is obtained when the input heat flux or the porosity is separately enhanced. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

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