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

how to set the density in mutiphase flow

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 16, 2005, 13:00
Default how to set the density in mutiphase flow
  #1
Chunning JI
Guest
 
Posts: n/a
Dear all cfders:

I use VOF method to simulate the mutiphase flows (air and water) base on the FEM method. I encountered a difficulty on setting the density. If the ratio of the parameter of air and water is smaller than 1:10, it converges, otherwise, it diverges. But, the actual case is 1:1000. In my procedure, the density is set to RhoA*(1-F)+RhoW*F, RhoA and RhoW are the density of air and water, respectively, and F is the volume fraction. Am i right? Moreover, in the single phase flows, the procedure works well. The model consists of the characteristic method+UZAWA type PCG method+VOF method. The problem is break dam, and all boundaries is slip type.

Thanks in advance!

Chunning JI
  Reply With Quote

Old   August 16, 2005, 13:12
Default Re: how to set the density in mutiphase flow
  #2
Junseok Kim
Guest
 
Posts: n/a
It is typical with high jump coefficient, so look at better solver for that case.

  Reply With Quote

Old   August 16, 2005, 22:21
Default Re: how to set the density in mutiphase flow
  #3
Chunning JI
Guest
 
Posts: n/a
Dear Junseok Kim:

Thank you very much. Can you recommend me a better solver or something about it. In my procedure, a Uzawa type preconditioned conjugated gradient method is adopted. Also, I wondered whether the model for sigle fluid can be transplated to the one for multiphase by only using variable density and viscosity of the fluid. If it is not true, what should be done?

Chunning JI
  Reply With Quote

Old   August 16, 2005, 23:11
Default Re: how to set the density in mutiphase flow
  #4
Chunning JI
Guest
 
Posts: n/a
Dear Junseok Kim:

In the multiphase flow, is the surface tension necessary? If it is omitted, would the result diverges?

thanks a lot.

Chunning JI
  Reply With Quote

Old   August 17, 2005, 00:49
Default Re: how to set the density in mutiphase flow
  #5
Junseok Kim
Guest
 
Posts: n/a
I am not sure about FEM version, but multigrid preconditioned conjugated gradient method is one good solver for finite difference.

In the free surace, i.e., the density and viscosity of one of phase is negligible, then you can use single phase solver with free boundary condition for pressure solver.

See the reference,

An investigation of the flow regime rsulting from splashing drops by David Morton, et al. Physics of fluids, vol 12 747-763.

  Reply With Quote

Old   August 17, 2005, 00:51
Default Re: how to set the density in mutiphase flow
  #6
Junseok Kim
Guest
 
Posts: n/a
If the surface tension is important, then it is necessary , but some cases, it is negligible.

Most of cases, surface tension is omitted, the solver is more stable.

  Reply With Quote

Old   August 17, 2005, 11:33
Default Re: how to set the density in mutiphase flow
  #7
Chunning JI
Guest
 
Posts: n/a
Dear Junseok Kim

Thank you for you advise and I will try it later. In you opinion, the pressure condition p=0 should be set on the free surface. I wonder whether the computational domain above the free surface (i.e., the element with f=0, f is the fraction) is also needed to set p=0. If the pressure of the domain above free surface is settled to zero, whether the velocity is also be enforced to zero?

Thank you very much.

Chunning JI
  Reply With Quote

Old   August 17, 2005, 13:05
Default Re: how to set the density in mutiphase flow
  #8
Junseok Kim
Guest
 
Posts: n/a
I didn't use one phase simulation, so would you refer reference paeprs?

  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
Problems with the density at walls for a compressible flow david39 OpenFOAM Running, Solving & CFD 0 February 8, 2010 13:33
SIMPLE algorithm for variable density flow mauz Main CFD Forum 1 May 15, 2009 15:13
Negative density problem. compressible flow Karl CD-adapco 2 July 10, 2008 16:41
Env variable not set gruber2 OpenFOAM Installation 5 December 30, 2005 05:27
Density variation Turbulent flow Parshant Dhand FLUENT 1 January 17, 2003 00:16


All times are GMT -4. The time now is 05:41.