[Sonia84]

Hi,

Please,
Could you help me?
I try to modelise the behavior of two phase flow in a pipe. And I don't know how to do this correctly.
The issue is:
In a pipe (DN 100) flows a vapor with a given flowrate (different flowrates will have to simulate).
At a givent time t appears (this is not modelise) a volume of water (1 liter) (at t the volume is unity, like a slug) with a defined velocity different of the vapor one.
I would like modelize :
- the behavior of the two phase flow along the pipe
- the velocity of the water phase

Must I use the VOF model, in transient ....
thank you for your help,

Sonia

[CFDtoy]

Hi there,
Could you present a schematic for this process? if you want to capture the exact interface of liquid - air , you should go for VOF. If you want to simulate mixing and provided that the velocities of the phases are pretty close ..use mixture model, else, use Eulerian-eulerian formulation to model the two phase flow.

btw, If it is something like liquid and gas flowing in the same duct - separately and you wnt to capture wave effects on the interface etc..should go for VOF modeling.


Thanks,

CFDtoy
visit http://cfdtoy.blogspot.com

Originally Posted by Sonia84

Hi,

Please,
Could you help me?
I try to modelise the behavior of two phase flow in a pipe. And I don't know how to do this correctly.
The issue is:
In a pipe (DN 100) flows a vapor with a given flowrate (different flowrates will have to simulate).
At a givent time t appears (this is not modelise) a volume of water (1 liter) (at t the volume is unity, like a slug) with a defined velocity different of the vapor one.
I would like modelize :
- the behavior of the two phase flow along the pipe
- the velocity of the water phase

Must I use the VOF model, in transient ....
thank you for your help,

Sonia

[Sonia84]

Hi,
thanks for your reply.

I attachment you could find a schema of my issue.
I want to capture the mix of the two flw and then the velocity of the phase ansd then the behavior of the flow (stratified, slug or droplets) in function of the distance foolowing the velocity of each phase.


thanks,

Sonia

[CFDtoy]

Hi there,
You should definitely consider using Eulerian-Eulerian scheme which will predict mixing of phases and + consider the velocity slip between phases. VOF scheme could work too - but when you impinge air and water, the initial level of disturbance can be captured only with very fine grids (drop formation etc) .Basic liquid slug flow with the droplet distribution (average distribution) can be figured using the Eulerian model.

with VOF it assumes the both the phases share the same velocity and mixed at the continuum level. Not sure if you want that.

But, if you want to predict droplets inside water or air bubbles in water to a fine level go for VOF.

The models are easy to set up and convergence for these problems can be achieved pretty well. So, may be you can try both methods and post results here.. Looks like a nice study for everyone to see which model gives the required result.

I have some information on VOF studies in my blog.

Let me know if you require any other information.

Thanks,

CFDtoy
Visit http://cfdtoy.blogspot.com

Originally Posted by Sonia84

Hi,
thanks for your reply.

I attachment you could find a schema of my issue.
I want to capture the mix of the two flw and then the velocity of the phase ansd then the behavior of the flow (stratified, slug or droplets) in function of the distance foolowing the velocity of each phase.


thanks,

Sonia

[CFDtoy]

Hi,
I came across this work on mixing / slug flow / droplet dynamics. Based on your flow profile VOF can be used. Take a look here

http://www.flow3d.com/pdfs/tp/micro_...i-Bib12-09.pdf


/CFDtoy
visit http://cfdtoy.blogspot.com

Originally Posted by CFDtoy

Hi there,
You should definitely consider using Eulerian-Eulerian scheme which will predict mixing of phases and + consider the velocity slip between phases. VOF scheme could work too - but when you impinge air and water, the initial level of disturbance can be captured only with very fine grids (drop formation etc) .Basic liquid slug flow with the droplet distribution (average distribution) can be figured using the Eulerian model.

with VOF it assumes the both the phases share the same velocity and mixed at the continuum level. Not sure if you want that.

But, if you want to predict droplets inside water or air bubbles in water to a fine level go for VOF.

The models are easy to set up and convergence for these problems can be achieved pretty well. So, may be you can try both methods and post results here.. Looks like a nice study for everyone to see which model gives the required result.

I have some information on VOF studies in my blog.

Let me know if you require any other information.

Thanks,

CFDtoy
Visit http://cfdtoy.blogspot.com

[ahmad786]

Originally Posted by CFDtoy

Hi,
I came across this work on mixing / slug flow / droplet dynamics. Based on your flow profile VOF can be used. Take a look here

http://www.flow3d.com/pdfs/tp/micro_...i-Bib12-09.pdf


/CFDtoy
visit http://cfdtoy.blogspot.com

CFD toy,
Hi CFD TOY.I am facing a hell of problems in simulating a flow in a steam turbine.The conditions for steam are:
1)-Dry saturated at inlet (P=5bar) of turbine with quality of "1"
Conditions of steam at the exit of turbine are :
2)-wet steam (P=1bar) with quality of "0.91"
Can u help me which model in CFX will be best in my case;
Secondly I am facing problems in assigning flow materials in CFX.
Currently I am using
"steam5vl" IAPWS -f97 libray as fluid material for my case.Is it right??
Should I use two materials steam gas and steam liquid from IAPWS library independently ??.Should I use homogeneous model or not?? Plz help me how should i assign flow materials for my case?? PLZ.