Understanding multiphase modeling (VOF) - Part 1

[@andremartins8384]

Dear József, sincere thanks for sharing this video with us! I'm very excited about learning OpenFoam and your videos are awesome, best regards from Brazil!

[@OpenFOAMJozsefNagy]

I am glad. Check out my channel, there are a lot more!

[@edwardvasquezmorales2028]

Bien Jozsef, felicitaciones y gracias. Un saludo desde Perú.

[@gordonfreeman7775]

Thank you very much for the amazing tutorial videos!! I just wanted to know how do we interpret the alpha values between 0 and 1. If the alpha value is say 0.05 at a location, does it mean that there is mist present there? As in is the simulation predicting there are small liquid droplets in the vapor at that location? Or do we interpret it as approximately 0 hence fully vapor?

[@OpenFOAMJozsefNagy]

It is a numerical value. Has nothing to do with reality. This is why the number of these cells should be kept to a minimum.

[@gordonfreeman7775]

@@OpenFOAMJozsefNagy Thank you for your response!! Which method would you recommend if one is interested in knowing how much liquid is carried over/entrained in the gas phase in form of mist or droplets?

[@sadikursiam2224]

Dear Nagy, i dont have the dynamicMeshdict file 12:36

[@jayangasamarasinghe4053]

Thank you very much for the descriptive tutorial. Could you please let us know how to change/ generate Alpha.water file.

[@OpenFOAMJozsefNagy]

I don't understand. Do you mean in which editor? In which way?

[@nikhilbhamare6761]

Yes sir yes. Magical water column. I really like your videos. 👌🏻👍🏻😄

[@shehabsalem-ho3bx]

Thank you very much for the descriptive tutorial. Could you please let us know how to change from Newtonian to non-Newtonian?

[@OpenFOAMJozsefNagy]

Change the entry from Newtonian to e.g. powerLaw and specify the coefficients.

[@joshmccraney4020]

Kind of a general question here, but is there a way to run interFoam until it reaches steady state and then run setFields again? I'll happily donate if you have a technique (I have before and will again).

[@OpenFOAMJozsefNagy]

Dear Josh, do you mean automatically or manually? Manually you can use a function object, which monitors the mean value of alpha in the volume and once you see, that the value is constant, you can stop the simulation and execute setFields. For the automatic version some kind of script or app could do the same, but this wold have to be set up.

[@joshmccraney4020]

@@OpenFOAMJozsefNagy This is what I tried but no luck. My controlDict specifies to startFrom latestTime. Then my setFieldsDict only specifies regions, which I make a different phase and a given value. So I begin the simulation as normal, stop it at some time, execute setFields with a different value than what was initialized, then execute interFoam. The simulation continues from the previous time but no change is made to the liquid/gas field. I'm using OF6

[@OpenFOAMJozsefNagy]

@@joshmccraney4020 I think possibly if you start a new case with 0 then it should work.

[@joshmccraney4020]

@@OpenFOAMJozsefNagy A new case with 0? You mean recomposePar and then rename the latest time folder 0? I did get it working with funkySetFields tho, which is nice!

[@sumitzanje5207]

How to calculate the void fraction for a pipe flow over time? Basically I want to plot "Time Vs. Void fraction" for a pipe carrying bubbly flow. I'm focusing on one particular section and want to determine void fraction in that section and how it changes over the time as bubbly flow is passing through it.

[@OpenFOAMJozsefNagy]

See my other response.

[@saketh79]

I have a problem in loading alpha.water values in paraview. I am seeing only 0 assigned to all points(including the box). But inside the file i see that 1 being assigned to points in the box and 0 to remaining points outside the box. I tried twice with setfields but it didnt work. Am I doing something wrong?

[@OpenFOAMJozsefNagy]

Paraview is confused by your orig file. Move it out of 0 and you will see alpha.

[@sandipgewali641]

After running the setFields utility, nano/gedit can't open the 0/alpha.water file. Despite that, I can see the water column in paraview. Still, why can not the nano/gedit read the 0/alpha.water file ?? It can't display the list of values of alphas for various cells. Instead the list seems cryptic with just "@" signs over there. The rest of the boundary conditions stay the same.

[@OpenFOAMJozsefNagy]

Try it with vim in the terminal

[@MedoZamalek1911]

thank you sir for this very useful tutorial .. i faced a problem that i couldnt get the different density of the water column and it is zero over the entire domain and i executed setFields line!!

[@OpenFOAMJozsefNagy]

Try and delete the orig file or move it out of 0

[@samahbendada6]

Hello. I am new at Open Foam. I tried to run this system and i did all of your steps, but I dont know why the alpha is zero at all time steps. I would appreciate your help in this problem.

[@OpenFOAMJozsefNagy]

Difficult to say without the case.

[@pacoespi]

Hi. Thanks for your video. It is very useful. Just one question: Can you please explain the difference between p and p_rgh, and how are both related and calculated?

[@OpenFOAMJozsefNagy]

p is the sum of p_rgh and the rho*g*h. So p_rgh is only the dynamic part of the pressure.

[@pacoespi]

@@OpenFOAMJozsefNagy Hi. Thanks. So I should be able to obtain the pressure as P = rho * (g*h + 0.5*u^2) ? I ask since I tried this already with post-processed data and the results were not the same.

[@DaylightDigital]

In the final VOF equation, what is u_r? What velocity is being referenced here?

[@OpenFOAMJozsefNagy]

This is the velocity, which is used for interface compression. Details can be found in the phd thesis of Henrik Rusche.

[@ntm90]

u_r is the relative velocity betwen the two phases. u_r = u_liquid - u_gas

[@zengchensun2628]

Hi sir. What is the 2S means in momentum equation?

[@OpenFOAMJozsefNagy]

Stress tensor. The factor 2 depends on the definition

[@avinashkumarverma7675]

after executing setFields command it is showing FOAM warning and no list of alpha values is appearing as you have shown in this video. What might the problem? Can you please explain? I have followed this tutorial of yours step by step.

[@OpenFOAMJozsefNagy]

Which version of OF do you use and what is the output?

[@DpointW]

Hi, I have a short and probably quite simple question about the presentation of the results of interFoam in Paraview. So there are two phases, air and water. To view only the water in Paraview, I use the clip function in conjunction with scalar and set the alpha value to 0.5. What I haven't quite understood yet is what this value stands for? Does this mean that all cells containing at least 50% water are displayed? In simulations with a finer grid, areas were also displayed in which there was no water according to the coarser grid. Or is this a clear indication that my grid is too coarse?

[@OpenFOAMJozsefNagy]

This is a drawback of the VOF method. Your questions are valid and usually there should be only one cell with 0.5 representing the surface, however due to numerics it is possible to have a smeared out surface. This is unphysical of course. You really have to make a compromise between resolution and run-time. This is also true for all commercial codes, this is not an OpenFOAM specific problem.

[@letstravelsomewhere]

I need to design Pipeline inspection Gauge for my final year - am i in the right track ?

[@OpenFOAMJozsefNagy]

Do you need multiphase models? If yes, than yes.

[@damonlee8135]

Thank you very much for such a detailed tutorial!

[@yusufpolat13]

Good work Man...

[@sumitzanje5207]

Hi I'm trying to solve two phase flow case. Case description: A horizontal pipe filled with water. From upstream end of the pipe say at a certain distance there is air tank supplying air into the horizontal pipe. I want to introduce the air with specific constant pressure and some desired volume. I want to push all the air from my tank into the horizontal pipe so that I can later quantify my results accurately (knowing exact volume used in different case files). The problem is to simulate this case i was trying to introduce a tank geometry on above horizontal pipe which was connected to air tank with one small vertical pipe. But as air has low density all air is not entering into the horizontal pipe (some on the top portion on tank, though air pressure is high initially). So Later I changed ma geometry and made tank below horizontal pipe. This allows complete air to get into the horizontal channel but now water is entering into the air tank and hence I'm not utilizing initial water volume used in the simulatiopn which is later very important for quantification of results. Is there any boundary condition I can use which just allow specific volume of air (time controlled air inlet) so that after certain volume or time that boundary not supplying any air into the horizontal pipe, something like this? Please let me know whats are the possible solutions.

[@OpenFOAMJozsefNagy]

Did you try the uniformFixedValue BC? There you can specify a csv file with time dependent data.

[@balapesar]

Dear Jozsef Greetings, Thanks for your interesting videos. I need to model a collision between a solid particle and a falling droplet. Based on existing experimental results after collision, particle start penetrating into droplet and create a very thin liquid film in shape of a hallow truncated cone around particle which is called lamella (whole the collision and lamella formation happens very fast ~ 1 ms) My alternative softwares for simulation are Fluent, OpenFoam, Comsol and Gerris. I'd like to get a piece of advice from you to know which of these softwares is more suitable for simulating this phenomenon (i.e. is able to predict lamella formation and its geometry more accurately) Here is some complementary information: - Droplet diameter is 2.8 mm and particle diameter is 2.0 mm - Droplet is falling by gravity and its velocity at collision is 0.8 m/s - Particle is moving horizontally with 8.0 m/s - Drop is water and particle density is 1050 kg/m3 I'm looking forward to hearing your helpful comments. Many thanks,

[@OpenFOAMJozsefNagy]

Sayed Hossein Banitabaei I have no experience whatsoever with Comsol or Gerris. I guess OpenFOAM and Fluent are rather similar, you will need VOF for your case. You will need a dynamic mesh refinement (available in OpenFOAM). Just try the damn break tutorial with mesh refinement and modify it to your needs. I guess your simulation will run for a while.

[@balapesar]

Dear József, Thanks for your reply. Since I do not have any experience for using "dynamic mesh refinement", would you please let me know at least one tutorial in each of the following subjects that can help me more in modeling droplet-particle collision: - VOF - Dynamic mesh refinement Your advice is really helpful and appreciated. My email address is: [e-mail] in case you can send any helpful document.

[@OpenFOAMJozsefNagy]

Sayed Hossein Banitabaei Check out the tutorials in OpenFOAM/OpenFOAM-2.3.0/tutorials/multiphase/interDyMFoam. If you are using another version than your path will be of course different to the tutorials. Take a look at constant/dynamicMeshDict within the cases. The magic happens there.

[@prakashachandrasahoo4618]

What is the procedure to calculate that impact velocity of droplet in numerical method?

[@OpenFOAMJozsefNagy]

You can start with the velocity field and the alpha field.

[@markcsete1570]

Dear József, I just followed every step of your video, and now at opening paraview the "Cell Arrays" are empty. It means, that the before given settings (0, constant etc.) are not used, right? What did I do wrong? - I cannot change the parameters on the top -

[@markcsete1570]

Ok everybody, please make sure to run the solver properly before asking! I did not run the solver and I paniced.. It is working now properly, making the 3rd denser mesh. Thank you József!

[@OpenFOAMJozsefNagy]

@@markcsete1570 I am glad it works!

[@prakashachandrasahoo4618]

Dear sir, how to calculate impact velocity of water droplet impacting on solid surface in Ansys fluent and what is range value of that droplet velocity?

[@ΝάσοςΜπαλαχτσής]

Hello! Nice video! I have completed a simulation where i get alpha vs time. How can I get volume vs time?

[@OpenFOAMJozsefNagy]

Use the integrate variables filter.

[@ΝάσοςΜπαλαχτσής]

@@OpenFOAMJozsefNagy Thanks a lot! One more question. Can you explain the reason why the integration of alpha gives the volume?

[@OpenFOAMJozsefNagy]

@@ΝάσοςΜπαλαχτσής Because the function calculates the volume integral of the cells filled by alpha.

[@ValenciaaaaaT]

Hi Jozsef, great video! I encountered a problem when executing setFields: it says that 'Field alpha.water is not found.' but i followed the steps correctly. Could i get some help?

[@OpenFOAMJozsefNagy]

Maybe rename 0.org to 0

[@raulgrunewald4055]

where did you collect the interFoam information that you show here from? I mean, is there an article or some official paper that explains in detail how interFoam works? or maybe some description of OpenFOAM about interFoam?

[@OpenFOAMJozsefNagy]

Mostly the source code, but the PhD of Henrik Rusche is also very helpful.

[@raulgrunewald4055]

Thanks!

[@DrMikeFoster]

Thank you for your work on this...very helpful. When I try to view the scalar contour, it only shows values of 0. I finally figured out that Paraview was reading alpha.water .org instead of alpha.water. As a fix, I just put the .org file somewhere else. Is there a way to tell Paraview to just use the non-.org file in the future?

[@OpenFOAMJozsefNagy]

If I understand your question correctly, paraview automatically selects alpha.water.org and you delete it, so it selects alpha.water instead. If you click Contour in Paraview, you will find under Properties "Contour By" and there you can select all your scalarFields.

[@DrMikeFoster]

Yes, once alpha.water.org is removed from the 0 folder, Paraview picks up alpha.water just fine. It seemed like when you went through, both alpha.water and alpha.water.org were both in the 0 folder, and Paraview picked up alpha.water instead of alpha.water.org. Do you know why it did that in your case?

[@OpenFOAMJozsefNagy]

Mike Foster As I mentioned, did you try and select alpha.water?

[@DrMikeFoster]

József Nagy If alpha.water and alpha.water.org are in the 0 folder, when I open foam.foam in Paraview all I see are values of 0 for the domain. If I then click on Contour, see that Contour By: alpha.water (and the Value Range shows only 0), and then click on Apply, the domain disappears from the graphics window. If I click on the eye icon next to foam.foam in the tree, the domain shows again. When I then click on Contour1 underneath it, I don't see any changes.

[@OpenFOAMJozsefNagy]

Mike Foster Well that's odd. I'm sorry, but It's difficult to solve the problem over youtube. Send me a screenshot to the mail adress, that you find in my about section!

[@haivandang4831]

I can do most of the video. but in final stage, after coding foam.foam. I cannot open foam.foam in paraview. Please let me know. Thank you for your support

[@OpenFOAMJozsefNagy]

It is just a simple text file with the ending ".foam" . Nothing special.

[@manas8603]

what's the difference between 0.orig and 0 , thanks

[@OpenFOAMJozsefNagy]

.orig is just a backup folder and is igrnored by the solver.

[@sushmajyothirmai2586]

sir , can we use this model to simulate gas-solid flow (two phase)??

[@OpenFOAMJozsefNagy]

No, not solid. There are the lagrangian solvers for that.

[@blind-tr1my]

Awesome videoes sir.....!!. Can u also do particle tracking in OpenFOAM? thanks

[@OpenFOAMJozsefNagy]

That is unfortunately one of the few topics I am not so familiar with. Sorry.

[@ابوعائشة-ج2م]

Can you help me please to simulate bubble column?

[@OpenFOAMJozsefNagy]

Did you check out my multiphase simulation project playlist?

[@007aha1]

to summarize this tutorial: "we dont talk about this"

[@bansishah2091]

the command "nano blockMeshDict" isn't working for me !

[@OpenFOAMJozsefNagy]

try to install it. Or use another text editor.

[@school771]

Hello I am tried to simulate two phase stratified (air-water) flow using VOF model with ANSYS FLUENT are you familiar with VOF model in ANSYS FLUENT code?

[@OpenFOAMJozsefNagy]

No, I'm sorry, I am not familiar. I guess it will be simliar to that of OpneFOAM, but I cannot guarantee it.

[@mayankbhuwal810]

Hello Sir :) I created the dummy file to open in paraview but unfortunately i am getting error that file cannot be open :(

[@OpenFOAMJozsefNagy]

Which version of Paraview do you use?

[@mayankbhuwal810]

4.4.0

[@OpenFOAMJozsefNagy]

I'm sorry, but I have no idea. Try maybe another version.

[@akshaypatil3462]

What does the prompt read?

[@aurelianfurcoiu2262]

Jozsef, how do you simmulate a wind tunnel?

[@OpenFOAMJozsefNagy]

I have never done it before. I would look for the geometry, mesh it, start with a steady state simulation and if transient effects are needed, use those results as iitial condition for the transient simulations.

[@aurelianfurcoiu2262]

Yes I would need a multiphase simulation as I want to determine the amount of condensation in the model test area

[@OpenFOAMJozsefNagy]

Wow, that is even more challenging. Start simple by replacing my stl files with yours and progress from there.

[@ing.nicola1706]

why alpha.water and not alpha.air ? what changes in fvsolution if i call it oil instead of water ?

[@ing.nicola1706]

the answer is exactly in kzbin.info/www/bejne/baiVnJeue6akbc0&list=PLcOe4WUSsMkF93STOampeX-U8hhgbFRbm&index=4 ...

[@OpenFOAMJozsefNagy]

You define it in constant/transportProperties. The first entry counts. You can change it though. YOu have to be consistent.

[@drjuanenrique]

József, thank you very much too...

[@rawaahazim8782]

what is the Governing Equations of VOF model?

[@OpenFOAMJozsefNagy]

An advection equation with a surface compression term.

[@anirban479]

hello...please sir discuss about bubble column simulation of multiphase modelling useing openFoam in your next video

[@OpenFOAMJozsefNagy]

I will post a video on more tutorials (also on updates of my tutorials) in the next couple of weeks, please stay tuned!

[@TheSouresh]

Hello, I would like to learn more about multi phase simulation in oopenFoam and about heat transfer simulations.Can you please help me.Any type of help will be appreciated.Thank You P.S. your tutorials are awesome.I learnt the basics of OpenFoam from your tutorials :)

[@OpenFOAMJozsefNagy]

Souresh Pal I am not sure how I can help. Watch the tutorials and modify them to your actual case. Otherwise you can google it. CFD Online is also a good starting point.

[@TheSouresh]

ok Thank You..By the way is it essential that my C++ knowledge should be very good? I know the basics of C.But it was never my strong point.But the CFD codes of openFOAM I understand them very well the ones you have explained in your tutorials.So please Advise...

[@OpenFOAMJozsefNagy]

No it's not essential. Only if you want to modify the models

[@SalaiSargunanSParamanantham]

thank you very for uploading this video. Can you upload pool boiling model video with three phase because i was struggle with last 3 months plz help

[@ChaitanyaArige]

Thank you very much Sir.

[@fitnessmythwalakaka]

Hi would it be possible to do this with oil and water? I

[@OpenFOAMJozsefNagy]

Sure. Only oil is easy, just change the material properties in transportProperties. However, there is also a solver for multiple fluids in OpenFOAM.

[@fitnessmythwalakaka]

József Nagy Thank you for getting back to me! Have a good day :)

[@OpenFOAMJozsefNagy]

I am glad to have helped!

[@OpenFOAMJozsefNagy]

If you know the interfacial tension bewteen oil and water you can give it a go, sure.

[@christiancosenza4091]

How can I do the same with comsol ?

[@OpenFOAMJozsefNagy]

I have no experience with comsol. But maybe give it a try in OpenFOAM. Here is a video, how to install it in Windows 10 : kzbin.info/www/bejne/rpuTlXWVhdh4osk

[@afauzia1993]

dear Jozsef, can you teach me about blockMeshDick position x y z in dambreak case? My proffesor give me task for change the dimension of dambreak case, and i dont know about dambreak using scale (convert to meters 0,146). can you make that tutorial video in your youtube? hehehehe, Thank you very much!

[@OpenFOAMJozsefNagy]

blockMeshDick? :D Which position do you want to change?

[@afauzia1993]

what i should say.. hahaha, i'm sorry. blockMeshdict.. That's file give our information about dimension of that case. in this case, we get a square result. for instance that position in blockMeshDict give : vertices (0 0 0) (1 0 0) (1 1 0) .... and, my proffesor told me to change that position until look rectangular. do you know about that? Thank you Jozsef.

[@afauzia1993]

i want to change dimension in after water coloumn, because, hopefully, i will get rectangular result..

[@OpenFOAMJozsefNagy]

You mean the obstacle?

[@OpenFOAMJozsefNagy]

Without the obstacle?

[@divyajyotibasu3001]

Hi Jozsef, amazing tutorial! Request you to create one on cavitation in a submerged bluff body in openFOAM. Regards!

[@DaylightDigital]

Here is a movie of this simulation at 1/6th real-time speed on the refined mesh. damBreak_refined: kzbin.info/www/bejne/l2rPd3Z9gdNne8k

[@sukiisue]

Pp