CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Accuracy of results

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 25, 2014, 15:22
Exclamation Accuracy of results
  #1
New Member
 
Jefferson Vieira
Join Date: Jul 2014
Location: Brazil/Scotland
Posts: 12
Rep Power: 4
Jefferson_dhv is on a distinguished road
Hello,

I'm trying to run a case in sonicFoam of a NACA 0012 airfoil, but I'm not being able to get accurate results, not even close to those expected regarding the CD. I tried to change some parameters, even the turbulence model, but I could not improve really much the results since I'm a recent new user of OpenFOAM. So I ask you what can I do to have more accurate results.

Here is the case:
/0
U
P
T
k
epsilon
mut
alphat

/system
controlDict
fvSchemes
fvSolution

The expected value for CD is around 0.008.

Thanks in advance,
J. Vieira
Attached Images
File Type: jpg coeffs.jpg (36.6 KB, 26 views)
File Type: jpg residuals.jpg (21.6 KB, 21 views)
Jefferson_dhv is offline   Reply With Quote

Old   August 31, 2014, 12:17
Default
  #2
New Member
 
miladrakhsha
Join Date: Aug 2012
Posts: 29
Rep Power: 6
miladrakhsha is on a distinguished road
Dear Jefferson,

I believe there was a very good topic in this page where people discussed the same thing. However, in short, you can never predict drag coefficient with a high Reynolds turbulent models. In order to accurately predict the drag you have to accurately resolve the flow close to the airfoil which needs y+<1.
Nevertheless, I would like to know whether or not you were able to predict the lift coefficient in the stall region for that particular airfoil.

Last edited by wyldckat; August 31, 2014 at 18:02. Reason: removed bold formatting from the whole text, to make it easier to read
miladrakhsha is offline   Reply With Quote

Old   August 31, 2014, 18:27
Default
  #3
New Member
 
Jefferson Vieira
Join Date: Jul 2014
Location: Brazil/Scotland
Posts: 12
Rep Power: 4
Jefferson_dhv is on a distinguished road
Hi miladrakhsha,

I appreciate your help. Since I've posted I improved a lot my results, the main problem was the quality of the mesh, the cells at the airfoil wall weren't thin enough and some discontinuities were causing numerical instabilities. At this moment I'm obtaining reasonably good results, but in my study I'm not watching the stall region, the interest relies on low angles of attack.

Best,
Jefferson Vieira
Jefferson_dhv is offline   Reply With Quote

Reply

Tags
accuracy, airfoil, convergence, naca, sonicfoam

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
Transient Run - Output "Time" in partial results? evcelica CFX 2 May 16, 2012 21:36
Varying time-step and Results freequency jstaylor89 CFX 1 April 17, 2012 02:00
CFX Varying time-step and Results freequency jstaylor89 Main CFD Forum 0 April 16, 2012 11:14
Lost Scenario Results..?? Fugacity Autodesk Simulation CFD 1 February 24, 2012 11:48
Problems with repeating results Lee CD-adapco 4 May 26, 2006 03:39


All times are GMT -4. The time now is 22:34.