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

The selection of model to solve a bubble rise in Fluent

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 9, 2010, 08:46
Default The selection of model to solve a bubble rise in Fluent
  #1
New Member
 
Jakub
Join Date: Mar 2010
Location: Czech Republic
Posts: 13
Rep Power: 7
Xilaf is on a distinguished road
Hi,

I simulate the air bubble rising in water column. I work with small (d=1mm) bubble. Can you tell me if the VOF model is acceptable in my case? I attached the the .jpg file with the situation at the beggining of the rising.

Thank you
Attached Images
File Type: jpg 1x6x2-0.jpg (47.1 KB, 54 views)
Xilaf is offline   Reply With Quote

Old   March 9, 2010, 11:28
Default bubble rise options - VOF n Eulerian Multi-Fluid approach
  #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
For single bubble simulations, kindly go ahead and use VOF type..it will provide you with surface deformation of the bubble and other local transients along the interface.

For cluster of bubbles rising ..use eulerian type and try increasing the bubble diameter if you want the bubbles to move up faster

/CFDtoy

Quote:
Originally Posted by Xilaf View Post
Hi,

I simulate the air bubble rising in water column. I work with small (d=1mm) bubble. Can you tell me if the VOF model is acceptable in my case? I attached the the .jpg file with the situation at the beggining of the rising.

Thank you
__________________
CFDtoy
CFDtoy is offline   Reply With Quote

Old   March 9, 2010, 11:57
Default
  #3
New Member
 
Jakub
Join Date: Mar 2010
Location: Czech Republic
Posts: 13
Rep Power: 7
Xilaf is on a distinguished road
I need simulate the rise velocity of small bubbles (0.5-2 mm).

These are the results from VOF:
A small bubble (d = 1 mm) rises in the simulation cca 30 mm/s. It is too slow. It should rise 200 mm/s, how can I see from literature (R.Clift at al,1978) and from experiment with camera.
A bubble d = 2 mm rises cca 200 mm/s. It should rise 300 mm/s.

In the VOF I can't set the drag coeficient. Is it possible to set it in another model?
You say Eulerian. And what about Mixture model?

I haven't worked with these models yet.

Thank you
Xilaf is offline   Reply With Quote

Old   March 10, 2010, 11:29
Default lifting effects
  #4
Senior Member
 
CFDtoy
Join Date: Mar 2009
Location: United States
Posts: 145
Blog Entries: 2
Rep Power: 8
CFDtoy is on a distinguished road
I understand your concern. The problem with lift of bubbles in, atleast vof case, is due to the density difference. Make sure you input the density values properly. Also, try and run different density values to see if the bubble rises faster.

It is true that you cannot set drag coefficient for VOF..the flow is homogeneous - ie..the liquid and gas share the same velocity field.

In the eulerian - two velocity fields for each phase applicable - using drag coefficient (or bubble diameter) effectively you can increase / decrease the bubble rise velocity. problem with this is that ..the interface of liquid-gas interface may be little smeared.

Now, i suggest the following, increase the grid density (if it is 2D then great..) twice and run eulerian multi-fluid approach - play with the drag and make sure you get the rate of bubble rise as you want.

btw, i did want to make sure you switched on gravity right?? Check how much flow you have in the system...is there a lot of flow (is it thermal driven flow ?? - if so try increasing the boussinessq coefficient - to enhance flow)..even with VOF this should work well if there is sufficient flow.

Hope this helps.

Regards,

CFDtoy

Quote:
Originally Posted by Xilaf View Post
I need simulate the rise velocity of small bubbles (0.5-2 mm).

These are the results from VOF:
A small bubble (d = 1 mm) rises in the simulation cca 30 mm/s. It is too slow. It should rise 200 mm/s, how can I see from literature (R.Clift at al,1978) and from experiment with camera.
A bubble d = 2 mm rises cca 200 mm/s. It should rise 300 mm/s.

In the VOF I can't set the drag coeficient. Is it possible to set it in another model?
You say Eulerian. And what about Mixture model?

I haven't worked with these models yet.

Thank you
__________________
CFDtoy
CFDtoy is offline   Reply With Quote

Old   June 19, 2013, 04:27
Smile can you teach me how to obtain the velocity of the bubble in FLUENT software?
  #5
New Member
 
jomin
Join Date: Jun 2013
Posts: 1
Rep Power: 0
jomin1986 is on a distinguished road
can you teach me how to obtain the velocity of the bubble in FLUENT software?
jomin1986 is offline   Reply With Quote

Old   November 21, 2013, 17:56
Question "How to monitor velocity single bubble rising in vertical column? "
  #6
New Member
 
Ali Masoudi
Join Date: Nov 2013
Posts: 4
Rep Power: 3
amasoudi is on a distinguished road
Hi,
Does anybody know how can I monitor rising velocity of a single bubble in a 2D column?
amasoudi is offline   Reply With Quote

Old   November 25, 2013, 15:29
Default
  #7
Senior Member
 
Join Date: Jan 2010
Location: Germany
Posts: 268
Rep Power: 8
Zaktatir is on a distinguished road
Look after the centroid of the isosurface equal to void*void and then track the velocity of the bubble.
Zaktatir is offline   Reply With Quote

Old   November 25, 2013, 15:49
Question
  #8
New Member
 
Ali Masoudi
Join Date: Nov 2013
Posts: 4
Rep Power: 3
amasoudi is on a distinguished road
Hi
Thank you for your answer but unfortunately I did not understand what you mean
amasoudi is offline   Reply With Quote

Old   December 1, 2013, 04:47
Default
  #9
Senior Member
 
Join Date: Jan 2010
Location: Germany
Posts: 268
Rep Power: 8
Zaktatir is on a distinguished road
Look after the centroid of the isosurface equal to void*void and then track the velocity of the bubble.
Zaktatir is offline   Reply With Quote

Old   December 4, 2013, 01:01
Default
  #10
New Member
 
Gaurav Yadav
Join Date: Oct 2013
Posts: 4
Rep Power: 3
gaurav4rt is on a distinguished road
Quote:
Originally Posted by jomin1986 View Post
can you teach me how to obtain the velocity of the bubble in FLUENT software?
In the left panel in ansys workbench fluent there will be MONITOR column. Click it and turn on the x y and z velocity fields and the continuity field and after doing the calculation click on countour button and in that select velocity as the criteria and click compute.It will show you the maximum and minimum velocity. Then click display...
gaurav4rt 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
[Other] How to compute the model by FLUENT and ANSYS njiit ANSYS Meshing & Geometry 1 April 21, 2010 18:05
H ow to compute the model by FLUENT and ANSYS njiit FLUENT 0 March 2, 2010 23:24
Fluent 12 k-w SST turbulence model DarrenC FLUENT 0 December 13, 2009 09:33
air bubble is disappear increasing time using vof xujjun CFX 9 June 9, 2009 07:59
Seeking Macroscopic Particle Model in Fluent bzhang7 FLUENT 0 May 27, 2009 13:36


All times are GMT -4. The time now is 01:32.