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

CD and CL values are way off, even though I've used inflation layers

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 30, 2013, 10:20
Default CD and CL values are way off, even though I've used inflation layers
  #1
Member
 
Bart A.
Join Date: Feb 2012
Posts: 45
Rep Power: 5
ziggo is on a distinguished road
I have a flow simulation where at low angles of attack (~10deg) the CL and CD values are very far from the reference data.
Simulation summary:

- Sharp edged flat plate like structure.
- Inflation layer on flat plate
- Standard k-epsilon model

At higher angle of attack (~40deg) the CL and CD values show resemble the reference data acceptably.
The error of low AoA CL and CD is not really dependent on the mesh. The error is there with 3 million cells, but also with 6 million cells.

I have applied inflation layers, refined the mesh and refined the timestep to no avail. What else can I do to get acceptable results?
ziggo is offline   Reply With Quote

Old   July 30, 2013, 12:09
Default
  #2
Senior Member
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 1,097
Rep Power: 19
flotus1 will become famous soon enoughflotus1 will become famous soon enough
There is a section in the FAQ that covers most of the factors influencing the result of a cfd analysis.

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
flotus1 is offline   Reply With Quote

Old   July 31, 2013, 02:23
Default
  #3
siw
Senior Member
 
Join Date: Jul 2009
Posts: 443
Rep Power: 13
siw will become famous soon enough
Change the turbulence model from k-epsilon to SST and make sure the mesh has a y+ = 1.
siw is offline   Reply With Quote

Old   August 5, 2013, 15:11
Default
  #4
Member
 
Bart A.
Join Date: Feb 2012
Posts: 45
Rep Power: 5
ziggo is on a distinguished road
@siw:

Thank you for the suggestion. I tried this out (calculated the first inflation layer thickness based on y+ with the CFD-Online calculator) but the CL and CD values only differ around 1% from the k-epsilon model with an y+ of 30.

This means that the coefficient values are still far from my wind tunnel reference data.
ziggo 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



All times are GMT -4. The time now is 05:57.