CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Meshing two-phase turbulent flow

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   December 20, 2009, 06:15
Default Meshing two-phase turbulent flow
  #1
Senior Member
 
Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241
Rep Power: 9
idrama is on a distinguished road
Hey folks!

I am simulate two-phase turbulent jet flow with VOF-Method. When I use a coarse mesh the simulation converge whereas the solution does not look physically correctly. But when I use a fine mesh, after a while of evaluation, the simulation aborts whereas the interface is captured fine until the time of abort. So is there something specific which I have to consider by meshing the domain? I am using a VOF-Method with and k-e realizable model.

cheers,

Claus
idrama is offline   Reply With Quote

Old   December 22, 2009, 17:52
Default turbulent VOF
  #2
Senior Member
 
CFDtoy
Join Date: Mar 2009
Location: United States
Posts: 145
Blog Entries: 2
Rep Power: 8
CFDtoy is on a distinguished road
Hi there,
what kind of VOF scheme are you using? turbulent VOF may provide more smooth surface and the disturbances at the interface may not be simulated that well using RANS modeling. a les type model will provide more accurate results here. btw, hav you tried running a laminar case?

regarding the convergence, i guess you just need to look into the setting / time stepping (variable / fixed ..courant number) etc.

mesh refinement imposes restriction on the Courant number and hence time stepping ..you may want to work on this direction..

/CFDtoy

Quote:
Originally Posted by idrama View Post
Hey folks!

I am simulate two-phase turbulent jet flow with VOF-Method. When I use a coarse mesh the simulation converge whereas the solution does not look physically correctly. But when I use a fine mesh, after a while of evaluation, the simulation aborts whereas the interface is captured fine until the time of abort. So is there something specific which I have to consider by meshing the domain? I am using a VOF-Method with and k-e realizable model.

cheers,

Claus
CFDtoy is offline   Reply With Quote

Old   December 22, 2009, 18:10
Default
  #3
New Member
 
Andrew Campbell
Join Date: Dec 2009
Location: Melbourne, Australia
Posts: 7
Rep Power: 7
acampbell is on a distinguished road
Are you running steady-state or transiently. Would suggest you need to run transiently to resolve this problem. Also what types of fluids do you have? velocities etc.
acampbell is offline   Reply With Quote

Old   December 24, 2009, 05:42
Default
  #4
Senior Member
 
Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241
Rep Power: 9
idrama is on a distinguished road
Hey peoples!

Currently, i am running it as a transient simulation whereby I am using the interFoam solver form OpenFOAM. The thing is that I am intend to simulate a jet srpaying into a vessel. I know preori which direction the jet takes, therefore, in this direction the mesh is set more dense. However, when I do so after a while of simulation time the simulation aborts. I assume it has something to do with the pressure because when the pressure evaluation step is supposed to start then the simulation stops. When the mesh is coarse the simulation runs with no problems to the end, however, I do not have a physically correct jet, i.e. the jet is distort.

I assume for a two phase flow the mesh has to be set skilful in order to avoid distortions of a phase and pressure problems. Note that the pressure in a two phase model is defined by p*:=p0+rho_i g where p0 is the total pressure, rho_i the density of pahse i and g the garvity.

Cheers,

Claus
idrama is offline   Reply With Quote

Old   December 24, 2009, 05:47
Default
  #5
Senior Member
 
Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241
Rep Power: 9
idrama is on a distinguished road
Additionally, I want to mention that when the simulation is going the collapse the time steps, adjusted by the Courant No., are getting smaller and smaller and smaller.

Cheers,

Claus
idrama is offline   Reply With Quote

Old   December 24, 2009, 16:29
Default
  #6
Member
 
B. Selenbas
Join Date: Dec 2009
Posts: 37
Rep Power: 7
bugra is on a distinguished road
hi everybody,

i' ve a problem simular as idrama, i want to simulate a nozzle problem includes water jet flow in air, 3d problem, i used unstructured mesh, in 2d section model, all the multiphase models are working. but in 3d, same models are not converged, i tried to solve unsteady and used Fluent, after about 30 iteration the continuity goes to 10^12. i take courent number default value, 0.25
i'm waiting for your helps,

thanks

bugra
bugra is offline   Reply With Quote

Old   December 24, 2009, 20:52
Default
  #7
Senior Member
 
Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241
Rep Power: 9
idrama is on a distinguished road
Hey Burga!

Do you realy mean continuity? I think that is total different to my one because positive continuity means that you have production of mass in your domain. In my case continuity is fine. The problem I have is that the simulations runs into a singularity, i. e. the velocity is going to blow up. The reason for that is: I do not know.

Cheers,

Claus
idrama is offline   Reply With Quote

Old   December 25, 2009, 04:12
Default
  #8
Member
 
B. Selenbas
Join Date: Dec 2009
Posts: 37
Rep Power: 7
bugra is on a distinguished road
Hi Claus,

you' re right, that's different, i'm still waiting for replys,

thanks

Bugra
bugra is offline   Reply With Quote

Old   January 23, 2011, 01:35
Default
  #9
New Member
 
zhenyan xia
Join Date: Jan 2011
Location: Tianjin,China
Posts: 6
Rep Power: 6
xiazhy is on a distinguished road
Send a message via MSN to xiazhy
Hi idrama

i am a fresher in OF..I also doing the same job just like you. but with a little difference, the turbulet model i need is LES. and the liquid phase is Non_newtonian liquid in my job. i want to know which solver i should use, and i hope i can get some adivce from you about LES+VOF+Non_newtonian. Thanks a lot ! any help whould be much appreciated!

zhenyan
xiazhy is offline   Reply With Quote

Old   January 23, 2011, 05:24
Default
  #10
Senior Member
 
Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241
Rep Power: 9
idrama is on a distinguished road
Hi,

as far as I see, you should use interFoam solver. In the turbulenceProperties dictionary, you just need to select LESModel. In constant/LESModel, e.g. Smagorinsky (You must look which is suitable for your problem), you need to select a LES model and a filter (Try to get Versteeg, Ferziger or Pope). Finally, in the dictionary transportProperties you have to select a model for non-Newtonian fluids: CrossPowerLawCoeffs or BirdCarreauCoeffs. For you problem, you should look for papers which are related to your problem to find best values for mu mu_inf etc.

I hope this helps!
idrama is offline   Reply With Quote

Old   January 24, 2011, 00:10
Default
  #11
New Member
 
zhenyan xia
Join Date: Jan 2011
Location: Tianjin,China
Posts: 6
Rep Power: 6
xiazhy is on a distinguished road
Send a message via MSN to xiazhy
HI idrama

Thanks a lot for your help. I will have a try according to your idea. thank you very much!


zhenyan
xiazhy is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Turbulent flow + VOF CK FLOW-3D 3 January 13, 2009 08:30
Two phase flow with phase change Ahmad Al-Zoubi CFX 1 November 26, 2008 04:59
Natural convection - Inlet boundary condition max91 CFX 1 July 29, 2008 20:28
Two phase flow models Atholl Main CFD Forum 2 May 7, 2002 03:49
fluid flow fundas ram Main CFD Forum 5 June 17, 2000 21:31


All times are GMT -4. The time now is 08:47.