CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

S2S Radiation Inaccurate for a simple parallel plate.... how do I improve accuracy?

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

LinkBack Thread Tools Search this Thread Display Modes
Old   April 12, 2023, 11:09
Default S2S Radiation Inaccurate for a simple parallel plate.... how do I improve accuracy?
New Member
Daniel B
Join Date: Jul 2014
Posts: 20
Rep Power: 11
bgp723 is on a distinguished road

I'm using FLUENT 2022 R1

I was investigating adding radiation to my CFD model, and I wanted to do some simple checkout cases to make sure I understood how FLUENT does radiation calcs.

I set up a two 1x1 m2 plates (one held at 300 K, other at 400 K BCs) separated by 1 cm facing each other to make sure FLUENT outputs correct radiative exchange heat flux (essentially, I'm trying to simulate two infinite parallel plate problem to make sure it matches hand calc).

I'm assuming that the fluid medium has no influence on the radiative heat transfer, so I'm using Surface to surface radiation model.

I was very taken aback by the results though, and I think I'm doing something wrong, but I don't know what.

I tried the following:
* Hot and cold plates at 1 emissivity -> ~990 W heat transfer at cold and hot. This is good. Hand calc says it should be 992 W
* Hot and cold plates at 0.1 emissivity (energy iter per rad iter: 10 [default], max num of rad iter: 5 [default])-> -17.3 W for cold plate, 84 W for hot plate. Solution converged very quickly. This made no sense! System energy balance is not retained, and hand calc says it should be 52.2 W.
* I tried the 0.1 emissivity case again but with energy iter per rad iter at 2 and max num of rad iter at 50, and 500. I got -47.3 W for cold plate and 57.3 W for hot plate. This is closer to hand calc, but there's net system energy imbalance of 10 W that just won't go away. I tried playing around a bit with radiation residual conv criteria and # of clusters, but they didn't resolve the issue.

Hmm, I would upload the file here, but it looks like the file size limit is very small... so I'm instead just attaching a screen shot showing this.
I would like to see if anyone else had similar issues using radiation in FLUENT.

Attached Images
File Type: png 2023-04-12_11-08-04.png (120.8 KB, 11 views)

Last edited by bgp723; April 13, 2023 at 14:30.
bgp723 is offline   Reply With Quote

Old   April 13, 2023, 14:44
Default Non-participating edges caused significant error
New Member
Daniel B
Join Date: Jul 2014
Posts: 20
Rep Power: 11
bgp723 is on a distinguished road
Ah, I have found an answer to my question.
I must have accidentally clicked off the radiation participation on the thin 1cm side walls enclosing the 1x1m plates participating in radiation.
Once I added that back in, the radiative heat transfer values now make sense and matches the analytical equation value.
I'm a little surprised that those thin side walls made that much difference, but I guess given the lower emittance, significant amount of rays were bouncing out of the domain.

One caution for others: it's not incredibly obvious to figure out how much radiative heat is leaking out the non-participating walls, which led me to believe that system level energy imbalance was improper.
bgp723 is offline   Reply With Quote


radiation, ray trace, s2s, surface to surface

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
Can S2S (surface-to-surface) radiation model include solid bodies in the enclosure? gcapp5893 FLUENT 0 March 18, 2023 11:02
[snappyHexMesh] shm in parallel with simple decomposition mihaipruna OpenFOAM Meshing & Mesh Conversion 6 July 16, 2015 04:55
Does using Parallel simulation improve Physics peter.pan Main CFD Forum 4 March 14, 2014 05:29
radiation module, no accuracy result Young FLUENT 0 February 18, 2009 04:11
Parallel Plate Rheometer vs Cone & Plate beginner Main CFD Forum 0 March 19, 2003 11:49

All times are GMT -4. The time now is 12:52.