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-   -   Inlet Boundary Conditions to model Slug flow in pipes (http://www.cfd-online.com/Forums/fluent/104659-inlet-boundary-conditions-model-slug-flow-pipes.html)

 A.Salih July 12, 2012 09:55

Inlet Boundary Conditions to model Slug flow in pipes

I am currently working on modelling slug flow in pipe with 90 deg. bend, simulating the two-phase flow of air & silicon-oil.

At the moment I am facing a problem in determining the inlet boundary conditions using FLUENT.

Basically, according to some peoples' work they set the inlet BC as Velocity-inlet and specified the superficial velocities and the volume fraction of liquid. ( of course the multiphase model is VOF).

But, when I try to set the velocity of phase1 (silicon-oil) and phase2 (air) I find that under the tap in which I should enter the values, a message appears saying that: " This page is not applicable under current settings".

Do you have any idea about what this might be from? and what should I do?

 Jabba July 13, 2012 16:18

Quote:
 Originally Posted by A.Salih (Post 371124) I am currently working on modelling slug flow in pipe with 90 deg. bend, simulating the two-phase flow of air & silicon-oil. At the moment I am facing a problem in determining the inlet boundary conditions using FLUENT. Basically, according to some peoples' work they set the inlet BC as Velocity-inlet and specified the superficial velocities and the volume fraction of liquid. ( of course the multiphase model is VOF). But, when I try to set the velocity of phase1 (silicon-oil) and phase2 (air) I find that under the tap in which I should enter the values, a message appears saying that: " This page is not applicable under current settings". Do you have any idea about what this might be from? and what should I do?

Are you working with only one inlet for both fluids?
When using VOF, it is recommended to set an inlet for each fluid separately.

I have tried to set up only one inlet using mass flow boundary condition, setting different mass flows for each fluid. At the entrance region, I cannot get a defined interface, something like a homogenous flow. At some place, it develops an interface and the slugs are formed.

I suggest that, if you try this method, extend your entrance region so the flow may develop and the slugs appear at some place before the bend.

I am not sure if it would get reliable results due to the homogenous characteristics of the flow near the mass flow boundary.

I believe that modeling two inlet for each fluid will be better. However, also you will have to model a development length just before the bend.

 A.Salih July 16, 2012 10:33

Hello Jabba,
Basically the experimental work which I am trying to simulate has one inlet for the both phases.
I have tried what you've suggested, to use Mass-flow BC, but the following message appeared: Global courant number is greater than 250.00 The
velocity field is probably diverging. Please check the solution
and reduce the time-step if necessary.

Can you please show me how to make an inlet for each phase so that I can give it a try?

and by the way, the distance from the inlet to the bend is about 5 m , so I guess it should be fine to achieve development.

 Jabba July 16, 2012 11:00

Quote:
 Originally Posted by A.Salih (Post 371653) Hello Jabba, Basically the experimental work which I am trying to simulate has one inlet for the both phases. I have tried what you've suggested, to use Mass-flow BC, but the following message appeared: Global courant number is greater than 250.00 The velocity field is probably diverging. Please check the solution and reduce the time-step if necessary. Can you please show me how to make an inlet for each phase so that I can give it a try? and by the way, the distance from the inlet to the bend is about 5 m , so I guess it should be fine to achieve development.

You may create a 3D model of a T or Y-shaped device and use the two inlets separetely.

It seems that your problem is related to the time-step size used. What is this value and also the size of your cell and fluid velocity?

 zainab August 2, 2012 14:44

Hello Jabba
I working on slug flow in horizontal pipe but the shape of slug not appears, I use one velocity inlet for the pipe, how can I setting separate inlets.
thanks.

 Jabba August 2, 2012 18:50

Quote:
 Originally Posted by zainab (Post 375093) Hello Jabba I working on slug flow in horizontal pipe but the shape of slug not appears, I use one velocity inlet for the pipe, how can I setting separate inlets. thanks.

you have to generate a 3D CAD model with two separate inlets merging in a single development tube

 zainab August 3, 2012 16:31

Hi every one
I am realy need to help, i working on modelling slug flow in horizontal pipe with FLUENT, but i never get the true phase distribution, what can i do? the time is v ery important for me, how can i modelling initially the stratified shape as in the figure below.http://http://my.yfrog.com/registrat...5017477d8577e2
thanks.

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