How can I make FLUENT solve 1D problem
 

Hi I have unsteady stratified two phase (air-water) flow in one dimension , I want to predict the change of phase velocities and volume fraction wiich both change with time and axial distance. I have a problem to how can I make FLUENT solve my case with one dimension only (i.e. with the axial distance a long the pipe) ? Is there anyone have idea about this?

Thanks all K. Saleem

Re: How can I make FLUENT solve 1D problem
 

Consider a plane flow in which only parameters in axial direction changes.In Engineering Practically speaking there are no 1D and 2D problems. they are just our assumptions and simplifications of actual 3D problems

Re: How can I make FLUENT solve 1D problem
 

Thanks to the replay. Can you tell me how can i consider my problem as a plane flow with more details?

Regards Saleem

Re: How can I make FLUENT solve 1D problem
 

One way to do this is to use 1 cell for your other dimesion when you create the model in Gambit.

Re: How can I make FLUENT solve 1D problem
 

Thank you bashu can you tell me how can i did this in more details? I think drawing 1 dimensional geometry not possible in Gambit.

Saleem

Re: How can I make FLUENT solve 1D problem
 

I think, for 1-D treament, just image the model consists of tank-in-series. Therefore, in Gambit, for X-Y-Z coordinate system, the grid interval for X-,Y-direction is set to 1. For Z-direction, you can assign the grid number you expected (say,120). Then, you will get the 1-D geometry in Gambit.However, in fluent, you should choose 2ddp/3ddp when starting this software. Evidently, for 1-D treatment, it is better to take 2-D meshing in Gambit (interval for X-direction equals unit, and for Z-direction is 120).

However, there are some things should be paid attention to.

(1)the momentum equation in X-direction should be deactivated;

(2)Whether the 1 interval assignment for X-direction will voliate some convergence (CFL, from grid discretization viewpoint). It is not clear to me. Since from 2d standpoint, the CELL aspect ratio under the predefined X-dir grid (=1) might too large or too small, depending on the system you simulated.

(3)The third problem is how the effect of boundary condition is imposed in the interior Z-dir fluid flow,especially for multiphase flow, say gas-solid two phase flow?

Re: How can I make FLUENT solve 1D problem
 

I ran a 1D case which I used for kinetics only. In other words I did not solve for the momentum equations and imposed the velocity/voidage profile on the domain. When I ran a single phase on this 1D domain, the results showed that the velcoity is not changing with length so I am not sure if you can solve the momentum equation.

I used a 2D case and the x direction had 1 cell (I don't think the dimension is important in x-direction), the y direction meshed it as usual.

Re: How can I make FLUENT solve 1D problem
 

I want to command about the replay to both of you:

Mr. Tondyn: 1)Can you tell me where can I find the grid interval in Gambit? 2)In my case I need to solve with the axial distance so I cannot ignore the momentum equation in the axial direction because usually as I did this no change of the velocity will happen? 3) When I asked about the ability to solve like this problem in 1 D my purpose from this is to solve at the interface region only along the pipe length. Such I have two phase air-water stratifed flow with unsteady state and I use the VOF model for this.

Mr. bashu: I asked you many times to how can I did one cell in x-direction?

Thanks a lot Saleem

Re: How can I make FLUENT solve 1D problem
 

I am sorry I assumed you are familiar with Gambit and you know where to find the mesh menu in Gambit.

As an example run this journal file in Gambit. Open a Gambit session, and then File --> read journal. It assigns a single cell in x-direction.

face create width 0.1 height 1 xyplane rectangle undo begingroup edge picklink "edge.3" "edge.1" edge mesh "edge.1" "edge.3" successive ratio1 1 intervals 1 undo endgroup undo begingroup edge picklink "edge.4" "edge.2" edge mesh "edge.2" "edge.4" successive ratio1 1 size 0.1 undo endgroup face mesh "face.1" map size 1

Re: How can I make FLUENT solve 1D problem
 

face create width 0.1 height 1 xyplane rectangle

undo begingroup

edge picklink "edge.3" "edge.1"

edge mesh "edge.1" "edge.3" successive ratio1 1 intervals 1

undo endgroup

undo begingroup

edge picklink "edge.4" "edge.2"

edge mesh "edge.2" "edge.4" successive ratio1 1 size 0.1

undo endgroup

face mesh "face.1" map size 1

Re: How can I make FLUENT solve 1D problem
 

Sorry i failed to open this can you send me it as journal file by the address khalidb77@gmail.com

Re: How can I make FLUENT solve 1D problem
 

Did you run the journal I sent before? You do not make a 1D geometry, but mesh one direction with one cell only.

Re: How can I make FLUENT solve 1D problem
 

No I failed to run the journal you sent. I asked you to send me it by the address below: khalidb77@gmail.com

Re: How can I make FLUENT solve 1D problem
 

Just copy these lines in a text file and then save it as a *.jou file, then run Gambit and read the journal file.

face create width 0.1 height 1 xyplane rectangle undo begingroup edge picklink "edge.3" "edge.1" edge mesh "edge.1" "edge.3" successive ratio1 1 intervals 1 undo endgroup undo begingroup edge picklink "edge.4" "edge.2" edge mesh "edge.2" "edge.4" successive ratio1 1 size 0.1 undo endgroup face mesh "face.1" map size 1

Re: How can I make FLUENT solve 1D problem
 

Unfortunately I still unable to make JOU file from text file because this extension not available under text file. I appreciate you to send me the jou file through my email to the last time. My email address is : Khalidb77@gmail.com

Re: How can I make FLUENT solve 1D problem
 

I should say that I cnnot tolerate the way of asking problem by Saleem.

If you tell me you have some technique problem after making some efforts, then ask bashu to get some solution. It will be understandable. Now, you are trying to rest youself on a untrying level;and ask Bashu several times for the simplest problem even after 10 days. Why not try by yourself and then ask some questions beyond that?

I should say that here I have no any intention to offend or attack anyone. Just give a unbiased comment.

Re: How can I make FLUENT solve 1D problem
 

Mr. Nime thank you for your advice. I want just to remind you this site designed to the all and we must not reduce the importance to every question even if it simple. So what the problem in my question if I not understood the answer from a person he was offered his help to me, second thing who tell you I did not make effort about this? I told Mr. Bashu I failed to make jou file from the text he sent me. So if you want to participate with us in a scientific discussion that's welcome and let the personal views away.

Re: How can I make FLUENT solve 1D problem
 

Hi,Saleem,

I highly respect the importance of your post. So,I suugest that you can make some efforts to read the Gambit help file which will definitely be useful for understanding the Bashu's meaning. And I am very glad to participate in the interesting discussion. My question is:

For case of gas-solid two phase flow, if adopting kinetic theory of granular flow model as well as using 1D model in Fluent, then how to evaluate the radial segregation effect imposed by the KTGF?

Because we know in this case, all the radial information is highly lumped. But from viewpoint of the mathematical model of KTGF, the radial distribution functions are still there. Therefore, from physical standpoint, I cannot unify the understanding of it.

Re: How can I make FLUENT solve 1D problem
 

Dear Nime: I have two phase (air-oil) flow into a pipe and I was used the VOF model to simulate my results. My need to use 1 D problem is due to predict the value of phase velocities and phase fractions along the interface region. So I think there was a difference between my case and yours because you have gas-solid flow and I am not familiar with the granular flow model so I cannot offer more help in this sorry.I hope you found the person who solve your problem. About my question to Mr. Bashu I understood what he mean and I open journal files before this time and I have no need to read the manual for this but the problem I cannot save the text he sent me as a journal file to use it by gambit so that I send this text below I am so thankful if you kindly save me it as jou file and mail me it by the address khalidb77@gmail.com

face create width 0.1 height 1 xyplane rectangle undo begingroup edge picklink "edge.3" "edge.1" edge mesh "edge.1" "edge.3" successive ratio1 1 intervals 1 undo endgroup undo begingroup edge picklink "edge.4" "edge.2" edge mesh "edge.2" "edge.4" successive ratio1 1 size 0.1 undo endgroup face mesh "face.1" map size 1

Re: How can I make FLUENT solve 1D problem
 

I try to reply the best I can. I think since we don't know each other personally there can not be any personal issues involved in our discussion. I also assume if anybody is posting any qustion in this forum, they can not solve it on their own. So here we go:

Dear Saleem, This is one way to create the journal file: Frist you copy the text in a text editor and save it with whatever name and extension that the editor allows you, then you can just click on the the file name and rename it as you wish with any extension as you want. I don't think that the extension of the file is important for gambit anyway!!

Each line is a command in gambit. I am resending the commands.

Just so you know, I don't think this is related to Gambit or Fluent or CFD in general. Sorry I do not want to send any separate emails.

face create width 0.1 height 1 xyplane rectangle

undo begingroup

edge picklink "edge.3" "edge.1"

edge mesh "edge.1" "edge.3" successive ratio1 1 intervals 1

undo endgroup

undo begingroup

edge picklink "edge.4" "edge.2"

edge mesh "edge.2" "edge.4" successive ratio1 1 size 0.1

undo endgroup

face mesh "face.1" map size 1

Dear Nime,

Re: How can I make FLUENT solve 1D problem
 

Dear Nime,

I posted my previous respond before replying to your part. I agree with you that a two phase flow can not be modeled in 1D unless the densities are so close to each other or the gravity (or other body forces) does not have any effect on the flow for various reasons. The radial segragation is the main reason these flows are difficult CFD cases and so if the effect of 2nd dimension is ignored I am not sure what is left. Now as you may know people are discussing whether the KTGF is the cause or effect of the radial segragation in vertical flows.

All said I still think if Saleem wants to try a 1D case he should go ahead and do it. The results should be studied very carefully since it may be too simplistic.

I ran a 1D fluent model but the flow was superimposed and all I cared about the model was to compare the kinetics that I had used in the UDF and verify the correctness of the equations with a 1D kinetic model.

Re: How can I make FLUENT solve 1D problem
 

Dear all,

In my test of 1D two-phase simulation, I found the solid mass fluxes of the inlet and outlet are not same under steady-state condition although the convergence criteria is satisfied. Now my questions are:

(1)what could be the possible reason for this problem? and what action should be taken for dealing with this?

(2)In addition, what kind of monitoring varibles are suited to judge whether the final results are convergent or not? In my simulation I used the area-integral gas/solid mass flux at different axial sampling section-area. Do you have other recommendation?

Please give your ideas.

Re: How can I make FLUENT solve 1D problem
 

Another example of 2-phase 1D run. Could you tell us more about phase properties?

In many two-phase cases the flow behavior is of oscillatory nature as the gravity and drag are acting against each other. There are other cases that you can reach a steady solution.

Check the mass balance over a period of time (3-5 times the period) and once the time average mass balance is zero, you have a quasi steady solution.

How does the mass flux that you are monitoring look like with time?

Re: How can I make FLUENT solve 1D problem
 

The gas-solid CFB sytem is air & FCC_particle. Their densities are 1.225 kg/m3 and 1700 kg/m3,respectively.

I do not try the time-averaged solution because it takes long time. So, I attacked directly for the steady-state solution. The monitored mass fluxes become level-off after a number of iterations. Ny the way,the viscous model in my simulation is laminar flow. The intial field is zero for all variables. That is all the details.

Re: How can I make FLUENT solve 1D problem
 

Unfortunately I don't have any explanation for the difference of mass flow rates in outlet and inlet if the monitor mass flux at different elevations are level and their values are equal and what you expect to get.

sloshing
 

hey im doing sloshing project.anyone know abt sloshing. i need some guidelines

Re: sloshing
 

what do you mean?

If the liquid is sloshing in a tank that also contains air or any other gas then it is a free surface flow and you need to use the multi-phase tools.

As you want to see how the fluid changes with time you need the unsteady solver.

Phil

Re: sloshing
 

hi, we can use FLUENT for sloshing.im working in it.do you know more abt sloshing. i just started my work.sudhir86@gmail.com is my id. plz contact me in that id.

Re: sloshing
 

i haven't worked directly on this but have you done all the multi-phase tutorials?

Re: sloshing
 

no. just learning basics in FLUENT.

Re: sloshing
 

doing the multiphase or VOF (I think) tutorials wouldn't take long and would give you these guidelines. Look into these methods in the user guide and see which is best suited.

WHY DON'T PEOPLE JUST DO THE TUTORIALS OR REFER TO THE USER GUIDE INSTEAD OF SAYING "DO MY WORK AND GIVE ME THE ANSWER ASAP! NO PLEASE OR THANKS".

Re: sloshing
 

One of my colleagues does free surface flows for his PhD so I would be best to forward your question to him. I'll get him to post a response on this thread in the next few days.

Phil

Problem with 1D problem
 

Hi everyone!!!

I am trying to simulate a 1d heat transfer in a medium confined between two large walls (top and bottom wall). I created a 2d rectangle in icem cfd. For top and bottom lines I have given the boundary conditions as walls. But I am not clear what boundary condition I should use for left and right lines which are not supposed to be present. (I created them only for meshing)..


Pls reply.