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

standart wall function Vs enhanced wall treatment

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 10, 2017, 06:32
Exclamation standart wall function Vs enhanced wall treatment
  #1
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
hi,

i have very simple 3d simulation: one inlet (vel in), one outlet (outflow), walls(no slip).

Rng ke with standard wall function gives very good results (compared with experimental).
but there are some papers in the literature says it is also possible with enhanced wall functions.

but it seems impossible and the whole simulation changes very much with EWT. i changed the mesh in a range from y+=0,2 to 5 but it is still exactly same.



does anyone have any idea about it? all parameters are same in both situation except "standart wall function" and "enhanced wall treatment" selection.
Attached Images
File Type: jpg Untitled.jpg (55.2 KB, 42 views)
gush is offline   Reply With Quote

Old   November 12, 2017, 08:47
Default no one?
  #2
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
anyone has an idea??
i am grateful for any comments
gush is offline   Reply With Quote

Old   November 12, 2017, 20:19
Default
  #3
Senior Member
 
Alexander
Join Date: Apr 2013
Posts: 398
Rep Power: 10
AlexanderZ is on a distinguished road
EWT usually is using with y+ 50..200

Best regards
AlexanderZ is offline   Reply With Quote

Old   November 13, 2017, 02:02
Default
  #4
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
Quote:
Originally Posted by AlexanderZ View Post
EWT usually is using with y+ 50..200

Best regards
i have never seen such an information about EWT! it is generally said that EWT needs dense mesh where y+ is about 1.

the interesting thing in my problem is in the case of high or low y+ values SWF gives the best results. but when EWT is activated then results differ very much as seen in the first post!!

i have found more or less the same problem mentioned in another post. swf and ewt gives very different results. and he thinks that it is because wall roughness somehow

wall roughness in enhanced wall treatment
gush is offline   Reply With Quote

Old   November 16, 2017, 17:07
Default
  #5
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 2,790
Rep Power: 35
LuckyTran will become famous soon enoughLuckyTran will become famous soon enough
What is this image of? Velocity mag or something?

It is odd the results are way different. You seem a sudden decay of (something) immediately after the inlet. This should have nothing to do with the wall treatment because it's not next to any walls.....

Quote:
Originally Posted by gush View Post
i have never seen such an information about EWT! it is generally said that EWT needs dense mesh where y+ is about 1.
I also have never seen any information saying EWT should be y+ 50.
LuckyTran is offline   Reply With Quote

Old   November 25, 2017, 10:13
Default
  #6
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
What is this image of? Velocity mag or something?

It is odd the results are way different. You seem a sudden decay of (something) immediately after the inlet. This should have nothing to do with the wall treatment because it's not next to any walls.....


I also have never seen any information saying EWT should be y+ 50.
this is the image of velocity contours in the mid plane!

1st image: standard wall function (coarse mesh, impossible to reach y+>30 because the velocity is too low. Re is about 630 for the inlet. results are very similar to experimental!!! )
2nd image: enhanced wall treatment (denser mesh near the wall y+=1)

nothing else is different in both simulation!

the question is, how does that sudden decay happen just with the selection of EWT (which seems wrong compared to experimental results) ?

p.s. you may say, "you got your results with SWF and it seems EWT is not suitable somehow for this specific case.". but there are many papers in the literature telling that EWT can also give good results.
gush is offline   Reply With Quote

Old   November 28, 2017, 10:00
Default standart wall function Vs enhanced wall treatment
  #7
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
the difference disappears at higher velocities.



Has anyone any idea about it?

Last edited by gush; November 28, 2017 at 13:47.
gush is offline   Reply With Quote

Old   November 29, 2017, 07:03
Default Not only y+ = 1
  #8
New Member
 
Ovid
Join Date: Oct 2016
Location: Spain
Posts: 28
Rep Power: 4
Fole is on a distinguished road
In some places it is pointed out that resolving the viscous and buffer layers is even more important than reaching an y+ value. I would play with the number of inflation layers to see what happens.

Keep us informed!
Fole is offline   Reply With Quote

Old   November 29, 2017, 10:02
Default
  #9
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
Quote:
Originally Posted by Fole View Post
In some places it is pointed out that resolving the viscous and buffer layers is even more important than reaching an y+ value. I would play with the number of inflation layers to see what happens.

Keep us informed!
thank you very much for the advice Fole!

now i am changing the number of inflation, hope it works!

the thing is there is no direct approach for this mesh issue. it is generally so case dependent and you must find the solution (if there is one) by trying only (which takes enormous time in some unique cases). (
gush is offline   Reply With Quote

Old   December 1, 2017, 08:53
Default
  #10
Member
 
yun
Join Date: Jul 2015
Posts: 36
Rep Power: 5
gush is on a distinguished road
Quote:
Originally Posted by gush View Post
thank you very much for the advice Fole!

now i am changing the number of inflation, hope it works!

the thing is there is no direct approach for this mesh issue. it is generally so case dependent and you must find the solution (if there is one) by trying only (which takes enormous time in some unique cases). (
different inflation numbers or any other change on the mesh did not effect the simulation results.

it seems at low velocities (Re is about 630) enhanced wall treatment is not able to give correct results while at higher velocities mentioned velocity issue is not a problem.

is there anyone here who has similar experience with EWT? or any advice is appreciated!
gush is offline   Reply With Quote

Old   December 4, 2017, 05:55
Post kwSST
  #11
New Member
 
Ovid
Join Date: Oct 2016
Location: Spain
Posts: 28
Rep Power: 4
Fole is on a distinguished road
If for such low velocities the turbulence level is low, try kwSST turbulence model which behaves well for low speeds. Also, a comparison between turbulence models could give more confidence in the results.

Regards.
Fole is offline   Reply With Quote

Reply

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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
OpenFOAM wall function treatment kimotbwb OpenFOAM Programming & Development 7 March 6, 2015 13:52
Applying enhanced wall treatment in free slip wall amarjogot FLUENT 1 June 26, 2013 13:44
error message with modeling a cube with a hold at the center hsingtzu OpenFOAM Native Meshers: blockMesh 2 March 14, 2012 10:56
ParaView for OF-1.6-ext Chrisi1984 OpenFOAM Installation 0 December 31, 2010 07:42
Enhanced Wall Treatment?? in Fluent 3d RRD FLUENT 1 June 4, 2009 09:45


All times are GMT -4. The time now is 06:38.