[aximefu]

In Fluent, There are two Multiphase Models：Euler-lagrange model and Euler-euler model. And Euler-euler model has three sub-model: VOF, mixture and euler, corresponding to specific different settings.

In CFX, there are free surface model, particle model, mixture model, Euler-lagrange and Eular-Eular model. Now I don't know if there is a similar sketch of Multiphase models in CFX? That is what is the relationship between several models above.

A thread about my question:
http://www.cfd-online.com/Forums/cfx/97226-vof-cfx.html

Do anyone have idea about this? Thanks!

[juliom]

Hi dear friend.
VOF is one of the most demanding model of multiphase fluid flow.
If you want to make a similar choose of this model in CFX, I recommed you to use Free surface+ particle or mixture model. These are Euler-Euler models.
BUT firstly you might research more about your physics, in order to know which is the model that fit better for your problem.
Regards Julio M

[aximefu]

Originally Posted by juliom

Hi dear friend.
VOF is one of the most demanding model of multiphase fluid flow.
If you want to make a similar choose of this model in CFX, I recommed you to use Free surface+ particle or mixture model. These are Euler-Euler models.
BUT firstly you might research more about your physics, in order to know which is the model that fit better for your problem.
Regards Julio M

I want to simulate the heat transfer and fluid flow in heat pipe, and I choose the free surface option in multiphase model. If water and vapor are set to be continuous phases, in Fluid Pair Models > Interphase Transfer the options I can choose are free surface and mixture. I use this two models to complete the computation, then the results don't seem to correct.
So was it ok to set both of water and water vapor to be continuous phases ?

[juliom]

Please send me your cfx case to figure ir out.
You might make some calculus and deduction before selcting the correct model, if not you will be trying to find a nedle in the dark!!!

[Ernesto10]

Hola Julio, yo igual tengo problemas con la configuración de los modelos a utilizar, lo que quiero simular es una tubería que descarga vapor(a 7MPa) en una piscina de agua. Tendrás algún ejemplo de un problema similar. Saludos.

[juliom]

Hola Ernesto.
Cada problema esparticular y requeire de diversos factores que se deben evaluar, como fracción volumetrica,distancia entre particulas entre otras cosas.
Tambien depende que tipo de vapor es, es vapor humedo o simplemente gotas de agua en una corriente de aire, como ves la morfologia es necesaria para escojer el mejor modelo.
En el caso que continue la discusión seria bueno que seguir en ingles para compartir la discusión con otros usuarios que quieran leer mas sobre el tópico.

[Ernesto10]

Ok, my problem is: i have 2 pipelines with steam (7 Mpa,540 °F, 100 kg/seg) this pipelines discharge in a pool water, i have used cfx and fluent but i have troubles with the models, in CFX:
this is that i have

-Multiphase model -free surface model standard

-Heat transfer -steam Saturation temperature
-water Thermal energy
-Turbulence -steam Zero equation
-water K-epsilon

-Interphase transfer Particle model
-Momentum transfer schiller Naumann
-Turbulence transfer none
-heat transfer Ranz Marshall

i'm sorry for my bad english

[juliom]

Dear Ernesto,
Here I see several problems, first of all you ened to verify you volume fraction because it is possible that you may have been used a bad model.. You need to be very clear when a model can be used and when not.
On the other hand the boundaries conditions, are bot pipe discharing at the same pool?.
Which are you boundaries condition?
Are you interested on the phase changes?
First of all you need to have very clear the goal of your simulation.!!!
How good is your mesh?

[mshf7]

would you mind helping me which modeling is more appropriat in analysing ship hull resistance?

[juliom]

Are you trying to simulate a kind of waves?.
In case you want to run a FSI, i recommend you to ask the question to other member, because I do not have much experience on FSI.

[ahmad786]

Originally Posted by juliom

Hi dear friend.
VOF is one of the most demanding model of multiphase fluid flow.
If you want to make a similar choose of this model in CFX, I recommed you to use Free surface+ particle or mixture model. These are Euler-Euler models.
BUT firstly you might research more about your physics, in order to know which is the model that fit better for your problem.
Regards Julio M

juliom,
Hi Juliom.I am facing a hell of problems in simulating a flow in a steam turbine in CFX.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??

[ahmad786]

Hi all
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??
Any one,plz reply.

[ahmad786]

Any One, to help .Please.

[ghorrocks]

You are modelling a high pressure ratio multiphase flow, including wet steam conditions. This is a very complex model and I trust you have plenty of time available to develop and validate it. But it is far too complex to realistically expect to get any help on the forum. If you want help on it I would try either a ANSYS training course on multiphase flows or contact ANSYS support.

[juliom]

Dear ahmad786
Sorry for my late answer I have been very busy these days.
First of all, this case is QUITE HARD, because it is not only multiphase flow. I mean, you have even mass transfer wich turns this case very hard.
AS you mentioned before, you have a quality of 1 and then at the outlet 0.91, as a result you have a mass transfer from one phase to the other. This is the difficult part here.
You need to develope a copde wich will be linked to the swolver to take this into consideration. I recommend to read more about it, i.e cooling tower which work under the same assumtion.
After you are able to handle this mass transfer the reaiming steps are easier. I agree with mr Glenn Horrocks, trying to get support from ANSYS.
My experience on multiphase fluid flow is more related to oil and gas where both phase are quite stable and the mass transfer rate is allmost negligible.

[vga67]

Hi everybody,

I want to simulate a water-air bubble model in CFX. Is mixture model in CFX a good choice for modeling such case?
thank you
Hamid

[Beginner_CFX]

Hello,
I tried to solve a problem of three layers of immiscible fluids such (water, oil and air). The top layer is air.
For that I tried two different ways:

1. I created a multiphase field in one domain. In this case I do not know how to define the location of each fluid. I need to specify an initial height of each fluid in the rectangular channel. I specified the free surface as shown in the tutorial. But I have no stratification like it should be as my flow is laminar for now. How to define from the start that the three fluid layers are stratified and immiscible?

2. The second method is with different domains related with an "interface domain". Each area is defined as multiphasic domain with an initial mass fraction of fluid equal to 1 for the fluid to be in this region.
The interfaces between the domains, I specify the conservation of flux. But when I apply a flow in the lower phase (water), it did not interact with the layers above.
Is this way better?
Do I have to specify anything about interfaces for interaction between fluids?
Do I have to specify the mesh deformation in interfaces?

Please, if you have handled this situation, do you have any advice for me.

Thanks

[juliom]

Hi Begineer_CFX. My best advise is to start always from a small problema or a scale of your final problem.
Try to do first a two phase problem. It will depend if your are going to use transient ot steady state formulation. Then you start adding more complexity to your problem. You will find a lot of resources in the literature.. For example this two: https://www.youtube.com/watch?v=YswJm2wFbP8
http://commons.erau.edu/cgi/viewcont...90&context=edt

Never start with the most complex problem. Finally, I cannot explain every single detail from your simulation because this forum is not meant to do it. Instead, try to come up with specific questions and try to adress each question at a time.
For example your mesh is something completly different to the model, but very important too..
Finally, your model definitely need to be VOF, more information at: http://www.afs.enea.it/project/neptu...tg/node290.htm
Dr. Ahmed AlMakky also has plenty information in his webpage, but do not contact him for a detailed explanation... you can find out more in http://cfd2012.com/ansys-gas-bubbles.html

I hope these examples that I share with you are fine. However, you will find a lot of work in the web, I do not recall the name of the engineer at ANSYS who has a lot of handouts in the web; his handout are very good. !!!

[Beginner_CFX]

Thank you Julio Mendez.

[bkm]

Originally Posted by ghorrocks

You are modelling a high pressure ratio multiphase flow, including wet steam conditions. This is a very complex model and I trust you have plenty of time available to develop and validate it. But it is far too complex to realistically expect to get any help on the forum. If you want help on it I would try either a ANSYS training course on multiphase flows or contact ANSYS support.

I want to do analysis of Evaporation and condensation of water into vapour and vapour to water....i am using two resistance model for heat transfer and evaporation and condensation model for mass transfer in fluent with euler multiphase model......with 3 phase like air vapour and water . i created one box there i patched water with half of portion of that rectangle box and i think fluent will assume remaining portion as vapour and air ...but when i am going for run there is no calculation for vapour why it so ? what i studied euler runs on 2 phase not on multiphase is it correct....well i will elaborate you my case...i have created prototype of my problem as one cube having 10 cm *10cm *10cm dim there i patched water vf 1 upto height of 5 cm side walls are adiabatic and bottom 325 k top glass is 320 k .... so plz help for it where i am making mistake.
thank you