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

ODD: no UDS flux across interior boundary

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 25, 2002, 09:15
Default ODD: no UDS flux across interior boundary
  #1
Bob
Guest
 
Posts: n/a
Dear,

I have the following problem when implementing a UDS (Fluent 5.5) for the settling velocity for solids in a clarifier.

The clarifier has an "interior" boundary. First, I solved (steady-state) the flow field without consideration of the UDS. Afterwards, I solved (unsteady) the UDS transport equation with the obtained flow field. The scalar was indeed transported as it should be, but it seems that the "interior" thread was acting as a wall for the UDS with zero concentration; the UDS simply did not cross the thread! If I look at the mass flow rate across this interior thread, I get a result but the net mass flow is zero (report -> fluxes), which is of course unrealistic...

Does someone have a wild idea what the cause might be? Is this an error inherent to Fluent?

Thanks a lot in advance! Cheers, Bob
  Reply With Quote

Old   February 25, 2002, 20:15
Default Re: ODD: no UDS flux across interior boundary
  #2
Greg Perkins
Guest
 
Posts: n/a
Hi Bob,

Not sure exactly what's happening, but here's some thoughts:-

Fluent uses control volumes, so it doesn't actually store the face values - and doesn't always store face fluxes. Thus, if you decouple the calculations, it may be that Fluent is no longer storing the face flux of the gas phase mass flow.

You can test this, by printing out the face fluxes returned by fluent and seeing if they are zero - or do something equivalent.

If this is the case, you may need to either: (1) re-couple the calculations or (2) re-calculate the face flux by interpolating the cell values to the faces. This is not that hard, but its a bit of a pain to do. (If you look in the Fluent 6 udf manual, they have some details on the gradient operators you can use - in Fluent 5 manuals here's no advanced documentation).

Alternatively, there might be a way to store the Fluent values somewhere during the first phase of calculation - but this will require a bit of thinking on how to do since there are multiple face fluxes per cell.

Well to be honest I'm not sure if this will help but it might give you some ideas.

Regards

Greg

  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
setting UDS Flux Andrew Garrard FLUENT 9 February 10, 2015 14:26
Doubts UDS Flux, UDS Unsteady for VOF model kel85uk FLUENT 0 March 17, 2010 09:53
UDS Flux Function Choice Yang Chung FLUENT 0 August 10, 2008 06:57
UDS flux through wall and interior face. shuqin FLUENT 2 July 29, 2006 03:54
Help with UDS FLUX Andrew Garrard FLUENT 2 February 14, 2005 06:47


All times are GMT -4. The time now is 03:48.