CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

how to set two bubbles using VOF method

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 7, 2008, 07:41
Default how to set two bubbles using VOF method
  #1
xujjun
Guest
 
Posts: n/a
I want to simulate the bubble using VOF method in CFX10.0,i have simulated the single bubble,but I want to know how to set two bubbles in initial boundary condition,,any help will be appreciated. thanks in advance

xjj
  Reply With Quote

Old   January 7, 2008, 18:15
Default Re: how to set two bubbles using VOF method
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

You can use the CEL expressions to define regions of fluid and gas. Either use a step function or a 3D interpolation function (cloud of points).

Glenn Horrocks
  Reply With Quote

Old   January 8, 2008, 08:51
Default Re: how to set two bubbles using VOF method
  #3
pankaj
Guest
 
Posts: n/a
Hi xujjun!

can u pls help me to formulate a steady state problem of multiphase for a single bubble in cfx?
  Reply With Quote

Old   January 8, 2008, 22:54
Default Re: how to set two bubbles using VOF method
  #4
HK
Guest
 
Posts: n/a
Hello, 1) Did you check the steady state terminal settling velocity compared to some theoretical calculation?

2) Did you monitor the recirculation of air inside the bubble?

HK
  Reply With Quote

Old   January 9, 2008, 07:08
Default Re: how to set two bubbles using VOF method
  #5
xujjun
Guest
 
Posts: n/a
Thanks,Glenn Horrocks,how to set the initial condition of the two bubble,i think that the two different regions on the bubbles need to set, i do not know that whether the subdomain region is used or not.

Hi,pankaj, I simulated single bubble using transient method, I am sorry i do not know how to simulate single using steady method.
  Reply With Quote

Old   January 9, 2008, 07:16
Default Re: how to set two bubbles using VOF method
  #6
xujjun
Guest
 
Posts: n/a
Hi,HK, i will compare the terminal settling velocity with some theoretical calculation, but there are few numerical results because of the too many time of the completing a case.
  Reply With Quote

Old   January 14, 2008, 06:55
Default Re: how to set two bubbles using VOF method
  #7
Andreas
Guest
 
Posts: n/a
You do not need subdomains for this. Use e.g. the sum of step functions as initial condition for the volume fraction of one phase:

step(((2. [mm])^2-x^2-y^2-z^2)/1. [m^2])+ step(((2. [mm])^2-x^2-(y-6. [mm])^2-z^2)/1. [m^2])

Then, two spherical bubbles with radius 2 mm are at x=y=z=0 and x=z=0, y=6 mm. Perhaps a piecewise linear step funtion (or a tanh function) is better than this discontinuous step...
  Reply With Quote

Old   January 14, 2008, 07:23
Default Re: how to set two bubbles using VOF method
  #8
xujjun
Guest
 
Posts: n/a
thanks Andreas, i will try using your method. recently, i simulated a single bubble of quiescent water in a closed tank using vof model, however, i found the volume fraction of bubble is decreasing with increasing time, the interface of bubble is blurry,even to disappear, my mesh is very good and the number of the meshes in a bubble is about 20, i think the mesh is very enough, i do not know how to do ?
  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
calculating Normal vector in level set method amir2920 Main CFD Forum 1 July 21, 2009 08:25
Fluent VOF Method - At a total loss advice required please LSF Main CFD Forum 5 April 13, 2009 22:56
using level set method rubby Main CFD Forum 2 March 7, 2009 03:02
Level set method for detonation Amir Main CFD Forum 1 July 2, 2008 16:25
VOF method on inter-tank transfer Louis FLUENT 0 March 14, 2006 10:28


All times are GMT -4. The time now is 14:04.