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

Forces (in controlDict) Giving Results 1/10 of Experimental Comparison

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 16, 2011, 22:30
Default Forces (in controlDict) Giving Results 1/10 of Experimental Comparison
  #1
Senior Member
 
Daniel
Join Date: Jul 2009
Location: Montreal, Canada
Posts: 151
Rep Power: 8
dancfd is on a distinguished road
Hello all,

I am running a simulation on a NACA 0012 airfoil, and after confirming that my simulation yields very similar Cp plots to the experimental results, I am now trying to match Cl to the experimental data. The case in question is at 13 deg alpha, and while I should be getting a Cl of ~1.34, the forceCoeffs.dat file shows 0.134. The Cd is also coming out negative...

The forces sub-dict of controlDict is as follows:

Code:
forces
    {
        type        forceCoeffs;
        functionObjectLibs ( "libforces.so" );
        outputControl outputTime;
        outputInterval 500;
        patches        (wing);
        pName       p;
        UName       U;
	rhoName	    rhoInf;
        log         true;
        rhoInf      1.177;
        CofR        ( 0.25 0 0 );//Center of rotation for moment calcs
        liftDir     ( 0 1 0 );
        dragDir     ( 1 0 0 );
        pitchAxis   ( 0 0 1 );
        magUInf     104.15;
        lRef        1;
        Aref        1;
    }
Note that my Uinf is (104.15 0 0). I would appreciate any advice anyone could offer.

Thanks,
Dan
dancfd is offline   Reply With Quote

Old   October 23, 2011, 22:16
Default Follow-Up
  #2
Senior Member
 
Daniel
Join Date: Jul 2009
Location: Montreal, Canada
Posts: 151
Rep Power: 8
dancfd is on a distinguished road
I will add some additional information:
Code:
                                                                                       Cd                  Cl                Cm
Results from OF:                                                               -0.0284      0.134      0.000628
Results from OF rotated to account for alpha:                       0.00247   0.1369     0.000628
Results from manually integrating Cp with spreadsheet:        0.01280	 1.167       -.00417
Results from Ref (NASA TM 4074 Table IV):                       0.01994     1.3939        0.0226
I have also attached a graph overlaying my CFD results with those from NASA TM 100526.

The graph of the Cp results suggest that the data should be accurate. However, integrating the data yields low results for Cd and Cl, while Cm is way off the mark. Is it just a coincidence that the OF Cl data is 10% of the experimental value?

Has anyone successfully integrated OF Cp results to yield Cl, Cd and/or Cm that are similar to experimental data?

I would appreciate any assistance that is offered. Regards,

Dan
Attached Images
File Type: jpg cp_steady-static-m3-a13-r6.jpg (29.5 KB, 25 views)
dancfd is offline   Reply With Quote

Old   November 14, 2011, 08:03
Default
  #3
New Member
 
Felipe
Join Date: Apr 2010
Posts: 13
Rep Power: 7
fippo_dk is on a distinguished road
The Aref is chordLength*width, so check that and run again your simulations, you may get better values after that.
Check also your Re number, it should be the same as in the transportProperties file.
fippo_dk is offline   Reply With Quote

Old   November 14, 2011, 20:11
Default
  #4
Senior Member
 
Daniel
Join Date: Jul 2009
Location: Montreal, Canada
Posts: 151
Rep Power: 8
dancfd is on a distinguished road
Thanks, there was a problem with the setup that fixed Cl. Cd and Cm have a greater error margin, though.

Dan
dancfd 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Comparing Experimental and Computational results. New Main CFD Forum 0 September 27, 2007 12:08
NACA0012 experimental results. Kyung-Seok, Kim Main CFD Forum 0 March 13, 2006 06:46
searching for experimental results Vignesh Main CFD Forum 0 August 18, 2003 20:32
Need experimental results on turbulent flow babyface Main CFD Forum 1 May 22, 2002 12:52
Valve Forces in CFdesign Mike Clapp Main CFD Forum 3 March 8, 2001 15:09


All times are GMT -4. The time now is 16:00.