[yulu]

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

[BlnPhoenix]

VOF model calculates only one velocity field, that of the mixture. So both phases share the same velocity.

[nadernaderi]

Originally Posted by yulu

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.

[hamed.majeed]

Originally Posted by nadernaderi

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.

[nadernaderi]

Originally Posted by hamed.majeed

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.

[hamed.majeed]

Originally Posted by nadernaderi

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?

[nadernaderi]

Originally Posted by hamed.majeed

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.

[granzer]

Originally Posted by nadernaderi

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.