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

reversed flow at outlet for bubble column

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

Like Tree1Likes
  • 1 Post By vinerm

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 2, 2020, 16:55
Default reversed flow at outlet for bubble column
  #1
Member
 
mln
Join Date: Dec 2019
Posts: 36
Rep Power: 2
melj is on a distinguished road
Hello

I am modeling a multiphase bubble column with turbulence using the Eulerian model.

1) The simulation converged initially for a few steps and then it stopped converging. It just runs for the specified no. of iterations. The residual value remains constant.

2) For every iteration, a message shows "Reversed flow on #### faces of pressure-outlet #."

Could anyone please let me know what these observations mean?

thank you
melj is offline   Reply With Quote

Old   March 3, 2020, 04:22
Default Convergence in multiphase
  #2
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 1,305
Blog Entries: 1
Rep Power: 21
vinerm is on a distinguished road
The residuals are not good indicators of convergence in multiphase flows. As long as those are below 1.0, those are good. What you should monitor are some averaged values for the field variables. If those stabilize, then, solution can be considered as converged.

As far as flow reversal is concerned, that could be just temporary or real. Until unless the flow-field is converged, you may observe some flow reversal. However, if the number of faces with flow reversal keep on reducing, then there is nothing to be worried about. If the flow reversal is maintained, then you may have to consider the appropriateness of the boundary. Either it is located too close to some internal obstruction or the pressure applied is too high.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared on the Forum
vinerm is offline   Reply With Quote

Old   March 3, 2020, 17:17
Default
  #3
Member
 
mln
Join Date: Dec 2019
Posts: 36
Rep Power: 2
melj is on a distinguished road
About the reversal of flow: I have modeled the bubble column to the height of liquid present in the column. So my outlet is essentially at the surface where liquid ends. To change my outlet I'll have to redo my geometry right?

I reduced the mixture gauge pressure to zero but the flow reversal still exists.
melj is offline   Reply With Quote

Old   March 4, 2020, 02:24
Default Degassing
  #4
Senior Member
 
vinerm's Avatar
 
Vinerm
Join Date: Jun 2009
Location: Nederland
Posts: 1,305
Blog Entries: 1
Rep Power: 21
vinerm is on a distinguished road
If you are modeling only up to the freeboard region, then you will always get flow reversal. Either extend the domain beyond freeboard region or use degassing boundary condition instead of outlet.
melj likes this.
__________________
Regards,
Vinerm

PM to be used if and only if you do not want something to be shared on the Forum
vinerm is offline   Reply With Quote

Reply

Tags
bubble column, reverse flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
reversed flow in xxxx faces on pressure outlet franzdrs FLUENT 8 January 4, 2020 20:12
Reversed Flow in Outlet JSped STAR-CCM+ 2 January 20, 2016 10:59
reversed flow when using Exhaust Fan as outlet Dziyad FLUENT 0 February 20, 2014 20:13
Reversed Flow in Outlet Steve FLUENT 18 March 30, 2013 07:50
Reversed flow at the outlet swati_mohanty FLUENT 0 January 5, 2011 01:00


All times are GMT -4. The time now is 23:42.