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

mass loss in Level Set

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 8, 2007, 03:09
Default mass loss in Level Set
  #1
dusky.he
Guest
 
Posts: n/a
I used Level set to simulate an uprising bubble in liquid. But the bubble is getting smaller and smaller.

Does anyone has this problem? I do not know the origin of the mass loss. It is from the Level set Eq. or from the accuracy of N-S

Thanks a lot
  Reply With Quote

Old   February 8, 2007, 05:53
Default Re: mass loss in Level Set
  #2
rt
Guest
 
Posts: n/a
This is well-known problem in LSM (due to numerical diffusion), (probably your literature review is very poor) thare are several treamtment as cure:

1. increase spatial resolution

2. increase accuracy of your JH solver (e.g. high order WENO + TVD RK)

3. Use Hybrid particle level set method for reducing diffusion (is really effective way)

4. Use spatially addaptive refinement near interface.

5. Use VOF instead of LSM !

  Reply With Quote

Old   February 8, 2007, 07:01
Default Re: mass loss in Level Set
  #3
qunwuhe
Guest
 
Posts: n/a
Thanks for your suggestion

Then it means it has no connection with NS solver

I used WENO+RT for LS eq. but it does not improve

I am thinking of using higher scheme for convective term in NS solver.

  Reply With Quote

Old   February 8, 2007, 07:55
Default Re: mass loss in Level Set
  #4
khan
Guest
 
Posts: n/a
This happen because of the volume dissipation. an alternate method is Allen-cahn model with lagrange multiplier or use of chan-hilliard model to control the volume dissipation of the bubble.

  Reply With Quote

Old   February 8, 2007, 08:32
Default Re: mass loss in Level Set
  #5
rt
Guest
 
Posts: n/a
>Then it means it has no connection with NS solver

it is clear that we expect mass-inbalance in the same order as we solve NS, in clear word based on residual of continuty satisfaction,

but LSM has usually severe mass lose, so sometimes bubble can be completely dissipated during advection. This is completely related to LSM not NS, e.g. if u switch from LSM to VOF u can preserve mass in accceptable manner (usually below 1% inbalance can be acheived).

>I used WENO+RT for LS eq. but it does not improve

I am not agree !

do you experience that with increase order of WENO mass loss is decreased, if no, certainly your imlementation is problematic because this fact is well-documented in literatures.

>I am thinking of using higher scheme for convective term >in NS solver.

Why?

if your velosity field is divergence free (bleow prescribed treshold), NS solver is fine ! (from mass-inbalance view point)

For simplicity u can forget NS and stick only to advection step, e.g. use rigid body advection test such as Zalesak's circle in the prescribed divergence-free velosity field, then study effect of high-order HJ solver and sitution of mass loss.

  Reply With Quote

Old   February 8, 2007, 10:00
Default Re: mass loss in Level Set
  #6
qunwuhe
Guest
 
Posts: n/a
Actually, I am using Cahn-Hilliard equation. The mass loss is severe.

I am trying to find the problem. I used steady flow field, there is no mass lost
  Reply With Quote

Old   February 8, 2007, 12:09
Default Re: mass loss in Level Set
  #7
Renato.
Guest
 
Posts: n/a
Are you redistancing the level set after each time step? I'm asking it because there are some mass correction algorithms that can be used when redistancing/rebuilding the level sets -- I have some references talking about it... the problem is to find ;o) .

Cheers

Renato.

  Reply With Quote

Old   February 9, 2007, 08:29
Default Re: mass loss in Level Set
  #8
qunwuhe
Guest
 
Posts: n/a
Mr. rt

Thank you so much

If possible, could you give me your mail address, I^d like to send you some results of my simulation.

Thanks

He
  Reply With Quote

Old   February 9, 2007, 09:40
Default Re: mass loss in Level Set
  #9
rt
Guest
 
Posts: n/a
rohtav@gmail.com
  Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to set pressure BC with mass Velocity Magnitud arwang FLUENT 2 March 12, 2007 21:04
Level set & distance functions Renato. Main CFD Forum 7 February 7, 2006 07:46
initialize level set ls newbie Main CFD Forum 0 March 17, 2004 15:17
Volume Loss in Level Set Method Zi-Wei Chiou Main CFD Forum 6 September 19, 2001 10:37
Level Set in Cavitation Modeling Niklas Wikstrom Main CFD Forum 1 September 9, 1999 14:08


All times are GMT -4. The time now is 00:14.