3rd Workshop on Advances in CFD and LB Modeling of

Interface Dynamics in Capillary Two-Phase Flows

October 8-12, 2018, Kobe, Japan

Ecole Polytechnique Federale de LausanneGraduate School of Engineering, Kobe Univerisity

The Japanese Society for Multiphase Flow

Workshop description

We are happy to present this workshop on the latestadvances in the computational modelling of the interfa-cial dynamics of capillary two-phase flow phenomena us-ing Computational Fluid Dynamics (CFD) and LatticeBoltzmann (LB) methods. In addition, experimentaltwo-phase flow visualization techniques will presented.The Workshop is now at its 3rd edition, following thefirst two editions in 2016 and 2017 that took place atthe EPFL in Lausanne, Switzerland.

The international team of lecturers is as follows:Prof. A. Tomiyama, S. Hosokawa and Prof. K. Hayashi(Kobe University), Prof. T. Seta (Toyama University),Prof. J.R. Thome (EPFL), Prof. G. Anjos (State Uni-versity of Rio de Janeiro) and Dr. M. Magnini (ImperialCollege London).

Direct numerical simulation of two-phase flows is anactive field of research since the beginning of the com-putational fluid dynamics in the early sixties. How-ever, thanks to the exponential increase of the computerperformance observed in the latest decades, the com-putational modelling of two-phase flows is advancingrapidly towards more complex and heterogeneous ap-proaches, thus yielding unprecedented insight into theessential aspects of the flow. CFD techniques modelthe flow at the continuum scale and consider a sharpgas/liquid interface with zero thickness. Intermolecularforces determining the interface physics are not directlycaptured, but their effect is modelled by introducing asurface tension force concentrated at the sharp interface.This workshop tackles in detail the most popular CFDtechniques to capture the interface dynamics across a

fixed computational mesh, i.e. Volume Of Fluid andLevel Set method, and a novel Arbitrary Lagrangian-Eulerian moving mesh methodology. Lattice Boltzmannmethods, instead of solving the Navier–Stokes equa-tions, solve the discrete Boltzmann equation to simulatethe flow of a Newtonian fluid using collision models toinvestigate the interfacial region’s thermophysics, andare thus also the focus of the present workshop. Quan-titative flow visualization techniques will be presented,which are pertinent to the experimental validation ofnumerical methods.

The global tendency towards miniaturization drivenby micro-electronics, as well as by the pharmaceuticaland fuel cell industries to name but a few, is bringingever greater attention to microscale two-phase flows. Inthis context, surface tension and phase change repre-sent important aspects that require ad-hoc numericalmodelling and are encompassed in this course. Thepresent workshop is addressed to Ph.D. students andpostdoctoral researchers involved in both experimentaland numerical investigation of two-phase flows, i.e. allthose who wish to get acquainted with the traditionalbackground and the most recent developments on theheterogeneous interface modelling strategies mentionedabove for capillary two-phase flows. These will be elab-orated by the leading scientists who will lecture onthe field of CFD and LB modelling of interfacial flows.The workshop is designed to promote interaction dur-ing and after the lectures: the participants are invitedto present their research in a dedicated session whichwill take place at the beginning of the week; practical“hands-on” sessions are scheduled on four afternoons,where the participants will apply and develop the codes

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provided by the lecturers to simulate benchmark flowconfigurations.

Workshop location and travel information

The workshop will be held at the Graduate Schoolof Engineering, Kobe University, Japan, which is lo-cated on the Rokkodai 2nd Campus. The lectureswill be in Room D1-201 on the 2nd floor of Sec-tion D1. Computers will be set up in the roomfor “hands-on” sessions. See the university web site:http://www.kobe-u.ac.jp/en/campuslife/campus guide/campus/index.html for more information.

Workshop registration and inscription fee

The workshop does not have any registrationfee in order to promote the participation of stu-dents/researchers. The link to the registration pagecan be found on the website of the Virtual Interna-tional Research Institute of Two-Phase Flow and HeatTransfer (VIR2AL). When registering, participants willbe invited to submit a brief personal overview of theirresearch and interests in two-phase flow. The registra-tion deadline is July 1st, 2018. You are encouraged toregister as soon as possible. A maximum number of 30participants will be accepted. As this is an advancedcourse, it is expected that participants already have aworking knowledge of numerical fluid mechanics.

Schedule and Contents of the lectures

MONDAY, 8 October

8:30-10:00 − Introduction to multiphase flow,Prof. A. Tomiyama. Fundamental equations for pre-dicting multiphase flows within the context of contin-uum dynamics are introduced in this lecture. Local in-stantaneous mass, momentum and energy equations andjump conditions at interfaces are derived from conser-vation laws and some integral theorems, and kinematicequations for interface tracking are deduced from a ge-ometric equation of surface, and averaged field equa-tions for multi-fluid and Euler-Lagrange models are de-rived from the local instantaneous equations and phase-definition functions. A simple method to derive semiempirical correlations and relevant dimensionless groupsfrom local instantaneous equations and jump conditionsis also introduced as a useful tool for developing a cor-relation from experimental or numerical data.

10:30-12:00 − Interface capturing methods, Prof.K. Hayashi. Interface capturing methods, i.e. theVOF and level set methods are introduced. Numeri-cal schemes for the advection and viscous terms and thePoisson equation commonly used in single and multi-phase flow simulations are briefly explained. The basesof the interface capturing methods are given in detail:especially, this lecture focuses on how to track the inter-face and to evaluate the surface tension force. Immersedboundary methods for particulate flows and flows in

complex channel geometries are also introduced.

13:00-17:00 − Hands-on session, Prof. K.Hayashi. Exercises with sample programs in C++ areprovided for better understanding of the concepts out-lined in the previous theoretical sessions.

17:30-19:00 − “My research in 150 s” and apero.Participants are invited to present their research in 150seconds (timing will be strictly enforced) in front of theclass in a clear, concise and straightforward manner,with the support of a two slides preloaded on our com-puter.

TUESDAY, 9 October

8:30-10:00 − Phase change modelling in inter-face capturing frameworks, Dr. M. Magnini.This lecture present an overview of the most popularmodels for including phase change within interface cap-turing frameworks. The background theory, tempera-ture boundary condition at the interface, and numer-ical implementation which are peculiar of each modelare discussed. The differences between microscale andmacroscale oriented formulations are debated. Math-ematical techniques for the smoothing of the phasechange source terms are introduced. Some typical val-idation benchmarks to assess the phase change modelsaccuracy are illustrated. Results of CFD simulationsaimed to investigate flow boiling within microchannelsare described.

10:30-12:00 − Advection schemes and surfacetension in VOF methods, Dr. M. Magnini. Thislecture presents an overview about the most employedadvection schemes for VOF methods, i.e. the PiecewiseLinear Interface Construction (PLIC) for sharp inter-faces and the Compression scheme for slightly diffuse in-terfaces. Theoretical background and numerical imple-mentation of both methods are presented. Afterwards,different methods for the curvature evaluation in theContinuum Surface Force (CSF) framework are intro-duced. The attention will be focused in particular to theadvantages and disadvantages of the classical implemen-tation, smoothing techniques, height function methodand higher order interface reconstruction method. Fi-nally, the VOF method implemented in the solver In-terFOAM of the open-source CFD toolbox OpenFOAMwill be illustrated, as an introduction for the afternoon“hands-on” session.

13:00-16:30 − Hands-on session, Dr. M.Magnini. This practical session shows how to set-up and run a two-phase flow simulation using the VOFmethod implemented in InterFOAM. Two benchmarkconfigurations will be simulated by the participants:(1) the breaking of a dam and (2) the rise of a Taylorbubble in a vertical tube.

WEDNESDAY, 10 October

8:30-10:00, 10:30-12:00 − ALE-FEM formulationfor two-phase flow, Prof. G. Anjos. These lec-tures aim to present the principles behind the Arbi-

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trary Lagrangian-Eulerian Finite Element Method for-mulation (ALE-FEM) for solving two-phase flows with amoving interface. An overview of the conservation equa-tions for two-phase flows written in a generalized formu-lation and the modelling of the interfacial forces will bepresented followed by an introduction to the FEM the-ory and the solution of a practical handmade 1D testcase.

13:00-16:30 − Hands-on session, Prof. G. An-jos. The participants will follow a demonstration withthe lecturer’s 2D ALE-FEM code for two-phase flows(based on the JCP’s article “A 3D Moving Mesh FiniteElement Method for Two-Phase Flows”).

THURSDAY, 11 October

8:30-10:00, 10:30-12:00 − Two-phase flow simu-lations using Lattice Boltzmann method, Prof.T. Seta. The Lattice Boltzmann method (LB) allowssimple numerical codes, easy parallel implementations,and fast computation of the multiphase flows with com-plicated boundary conditions. The overview of the LB isgiven, followed by the theoretical fundamentals includ-ing the Chapman-Enskog expansion employed to derivethe Navier-Stokes equations. The comprehensive reviewof the popular multiphase Lattice Boltzmann methodsand the boundary conditions dealing with wettabilityare introduced. The accuracy and robustness of themodels are explained in detail to enable the studentsto construct the LB model to address problems they areinterested in.

13:00-16:30 − Hands-on session, Prof. T. Seta.Some FORTRAN codes for multiphase LB models arepresented in a hands-on session for understanding theadvantages and disadvantages of each model.

FRIDAY, 12 October

8:30-10:20 − Optical measurements for valida-tion of numerical simulation of two-phase flow,Prof. S. Hosokawa. Experimental data are requiredfor validation of models used in numerical predictionsof two-phase flows. Since optical measurement methodssuch as laser Doppler velocimetry and image processingmethods are invasive and do not affect flow character-istics, they are frequently used for the validation. Inthis lecture, fundamentals of the measurement methodsare explained and examples of validations of numeri-cal predictions are presented to discuss the points tonote in comparison between measured and predicted val-ues. Advanced methods such as a small LDV probe andspatiotemporal filter velocimetry are also introducedto demonstrate their potential for validating numericalsimulations.

10:40-12:30 − Measurement and image process-ing techniques for quantifying two-phase flows,Prof. J. R. Thome. This lecture will give an overviewof several experimental techniques developed within theLTCM lab for two-phase flow visualization and imageprocessing. The 1st technique is for the measurement

of dynamic void fractions in stratified and slug flowsin horizontal tubes, using a laser sheet and high speedcamera together with image processing to overcome therefractive index effect of the channel to the test liquid(refrigerants). The 2nd technique is for characterizingmicro channel two-phase flows to determine: flow pat-tern, bubble frequency, bubble length, bubble velocity,bubble coalescence rates and indirectly the void frac-tion (bubbly and slug flows only), using a pair of lasersand diodes with signal processing. The 3rd techniquein referred to as the “time-strip” method, that is animage post-processing method for high speed videos oftwo-phase flows, particularly suited for characterizingbubbly and slug flows. The 4th technique is micro-Particle Shadow Velocimetry, in which the shadows ofparticles are tracked from behind using LED lighting,rather than micro-PIV with front lighting by a laser re-quiring fluorescent particles, to obtain: bubble shapes,velocity flow fields, etc. Quantitative measurements areobtained for creating test cases for numerical validationsand for the building of mechanistic models.

The lecturers

Prof. K. Hayashi is AssociateProfessor at the Graduate Schoolof Engineering, Kobe University,Japan, since 2012. He was for-merly Assistant Professor (2007-2008) and then Lecturer (2008-2009) at the Kobe City College ofTechnology, and Assistant Profes-sor at the Kobe University (2009-2012). His research focuses ondeveloping numerical methods for simulating compli-cated motions of bubbles and drops and correlationsbased on the bubble and drop mechanics.

Prof. A. Tomiyama is Pro-fessor at the Graduate Schoolof Engineering, Kobe University,Japan, since 2003. He was for-merly researcher at the EnergyResearch Laboratory at HitachiLtd. between 1984 and 1988, thenAssistant Professor (1988-1991)and Associate Professor (1991-2002) at the Kobe University. In2011 he became Vice Dean at the Graduate School ofEngineering, Kobe University, and Dean since 2015.His research interests are experimental and numericalinvestigation of multiphase flows in nuclear reactors,chemical plants, fuel injectors and environmental sys-tems.

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Dr. M. Magnini was a post-doctoral research assistant at theLTCM at the EPFL, Switzerland,from 2012-2017 and is now a post-doc at Imperial College London.He received a M. Sc. degree inmechanical engineering in 2007from the Alma Mater Studiorum- Universita di Bologna, Italy, anda Ph.D. degree in Energy Engineering in 2012 from thesame institution. His research focuses on numerical sim-ulations of two-phase flows with phase change withinmacro and microchannels and theoretical modelling ofevaporation in microchannel slug flow.

Prof. G. Anjos is Professorof Mechanical Engineering at theState University of Rio de Janeiro(UERJ), Brazil. He received hisM.S degree in Mechanical Engi-neering from the Federal Univer-sity of Rio de Janeiro (UFRJ)and the Ph.D. degree at the SwissFederal Institute of Technology(EPFL). His doctoral thesis hasbeen nominated for the EPFL best thesis award of 2012and it has been published in the renowned Journal ofComputational Physics in 2014. Additionally, Prof.Anjos has worked as Post-Doc at the MassachusettsInstitute of Technology (MIT). His research interestsinclude two-phase flows, scientific computing, fluid dy-namics and heat and mass transfer. He is member ofthe Brazilian Society of Mechanical Sciences and Engi-neering (ABCM).

Prof. T. Seta is Associate Pro-fessor at the Graduate Schoolof Science and Engineering forResearch, University of Toyama,Japan, since 2007. He was for-merly a researcher at the IBM T.

J. Watson Research Center (1996-1997), researcher atthe Institute of Applied Energy (1997), Lecturer at theShizuoka Sangyo University (1998-2001), and Lecturerat the University of Toyama (2001-2006). His researchinterests include numerical modeling of dynamics of liq-uid water on hydrophobic and hydrophilic surfaces, andnumerical investigation of the accuracy, stability, andefficiency of Lattice Boltzmann methods for heat andmass transfer.

Prof. J. R. Thome is Profes-sor of Heat and Mass Transferat the Swiss Federal Institute ofTechnology in Lausanne (EPFL),Switzerland, since 1998, wherehis primary research interests aretwo-phase flow and heat trans-fer, covering both macro-scale andmicro-scale heat transfer (boilingand condensation). He is chair ofthe Virtual International Research Institute on Two-Phase Flow and Heat Transfer (VIR2AL). He was alsothe Director of the ERCOFTAC European Coordina-tion Center (European Research Community On Flow,Turbulence And Combustion) with about 180 affiliateduniversities, research centers and industrial companies,resigning this position in 2011.

Prof. S. Hosokawa is AssociateProfessor at the Graduate Schoolof Engineering, Kobe University,Japan, since 1998. He was for-merly Assistant Professor at theKobe University (1993-1998). Hisresearch interests include develop-ment of optical measurements forsingle and multiphase flows, tur-bulence in dispersed two-phase flows, motion of fluidparticles, mass and momentum transfer at an inter-face and generation method and application of micro-bubbles.

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