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VoF model, two phases, but only able to show velocity of the phase "mixture"?

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Old   June 8, 2017, 06:22
Question VoF model, two phases, but only able to show velocity of the phase "mixture"?
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Yu Lu
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Hi all

I'm working on a simple simulation where two immiscible liquid flows in a pipe. I'm using VoF model with two phases (both liquid, immiscible, properties separately defined, surface tension force modelling enabled).

When I was trying to check some results, the volume fraction contours of both phases shows fine. However the contours or vectors of velocity can only choose the phase "mixture" instead of my two phases in the "phase" drop-down list. Why is this?

Many thanks
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Old   June 8, 2017, 09:11
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VOF model calculates only one velocity field, that of the mixture. So both phases share the same velocity.
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Old   March 23, 2018, 07:21
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Quote:
Originally Posted by yulu View Post
Hi all

I'm working on a simple simulation where two immiscible liquid flows in a pipe. I'm using VoF model with two phases (both liquid, immiscible, properties separately defined, surface tension force modelling enabled).

When I was trying to check some results, the volume fraction contours of both phases shows fine. However the contours or vectors of velocity can only choose the phase "mixture" instead of my two phases in the "phase" drop-down list. Why is this?

Many thanks
That's true, you can only see velocity for mixture. However you can make new variable in CFD post to see only velocity of water/air.
Here is the way that you need to follow in CFD Post:
- Expressions- New- phase2 volume fraction * velocity
(In order to avoid typo you can choose different parameters by right clicking in free area)
- variables- new - select expression that you made in previous step
Now you will see that you have new variables that only shows your phase2 velocity.
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Old   March 24, 2018, 10:54
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Hamed Abdul Majeed
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Quote:
Originally Posted by nadernaderi View Post
That's true, you can only see velocity for mixture. However you can make new variable in CFD post to see only velocity of water/air.
Here is the way that you need to follow in CFD Post:
- Expressions- New- phase2 volume fraction * velocity
(In order to avoid typo you can choose different parameters by right clicking in free area)
- variables- new - select expression that you made in previous step
Now you will see that you have new variables that only shows your phase2 velocity.
This shouldn't be phase 2 velocity!
You cannot get phase 2 velocity as you solved a shared velocity field to begin with.
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Old   March 24, 2018, 10:59
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Originally Posted by hamed.majeed View Post
This shouldn't be phase 2 velocity!
You cannot get phase 2 velocity as you solved a shared velocity field to begin with.
You solved a shared velocity field, but it doesn't mean that in the results you can not see only one of the phases velocity!!
you are telling cfd post to show you only on of the velocities. It doesn't have anything to do with solution method and calculation processes.
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Old   March 25, 2018, 11:28
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Quote:
Originally Posted by nadernaderi View Post
You solved a shared velocity field, but it doesn't mean that in the results you can not see only one of the phases velocity!!
you are telling cfd post to show you only on of the velocities. It doesn't have anything to do with solution method and calculation processes.
Yes, you will get a value of velocity as you multiply phase fraction (a number) with mixture velocity (m/s).
But my point is, would that be a representation of phase 2 velocity or not?
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Old   March 25, 2018, 11:31
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Quote:
Originally Posted by hamed.majeed View Post
Yes, you will get a value of velocity as you multiply phase fraction (a number) with mixture velocity (m/s).
But my point is, would that be a representation of phase 2 velocity or not?
Yes! it would be.
give it a try and you will see the results.
Cheers.
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Old   December 25, 2021, 08:35
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Quote:
Originally Posted by nadernaderi View Post
That's true, you can only see velocity for mixture. However you can make new variable in CFD post to see only velocity of water/air.
Here is the way that you need to follow in CFD Post:
- Expressions- New- phase2 volume fraction * velocity
(In order to avoid typo you can choose different parameters by right clicking in free area)
- variables- new - select expression that you made in previous step
Now you will see that you have new variables that only shows your phase2 velocity.
This wouldn't give the velocity of the different phases. It would just weight the mixture velocity with phase fraction. If you want velocity fields of different phases better to use Euler-Euler 2 liquid model. Not sure if it will work for immiscible liquids though.
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