|
[Sponsors] |
Correct pressure distribution but wrong aerodynamics coefficients |
![]() |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
![]() |
![]() |
#1 |
New Member
Juanito
Join Date: Oct 2010
Posts: 27
Rep Power: 16 ![]() |
Hello to everybody.
I have been working with OpenFOAM and I have a strange problem. I have simulated several times a 2D cylinder, with different meshes and solvers and I always obtain a correct pressure and velocity results but a too small drag coefficient. I have calculated it by hand, sampling the pressure over the cylinder, and then the drag coefficient is ok. Where could be the problem? In literature Cd for a cylinder with our Reynold is about 0.8 but forceCoeffs function calculates 0.3. This our controlDict file: ---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object controlDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // application simpleFoam; startFrom latestTime; startTime 0; stopAt endTime; endTime 600; deltaT 1; writeControl timeStep; writeInterval 50; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression uncompressed; timeFormat general; timePrecision 6; runTimeModifiable yes; functions ( forceCoeffs { type forceCoeffs; functionObjectLibs ("libforces.so"); //outputControl outputTime; //outputInterval 1; outputControl timeStep; outputInterval 1; patches (paredes); //change to your patch name rhoInf 1.225; CofR (0 0 0); liftDir (0 0 1); dragDir (-1 0 0); pitchAxis (0 0 0); magUInf -50; lRef 1; Aref 1; } forces { type forces; functionObjectLibs ("libforces.so"); // Lib to load //outputControl outputTime; //outputInterval 1; outputControl timeStep; outputInterval 10; patches (paredes); // change to your patch name rhoName rhoInf; rhoInf 1.225; // Reference density for fluid CofR (0 0 0); // Origin for moment calculations } ); // ************************************************** *********************** // Any suggestions. Thank you. |
|
![]() |
![]() |
![]() |
![]() |
#2 | |
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 368
Rep Power: 20 ![]() |
Quote:
Hope this helps V. |
||
![]() |
![]() |
![]() |
![]() |
#3 |
Member
Rasoul
Join Date: Feb 2010
Posts: 32
Rep Power: 16 ![]() |
I'm not sure. But for me this values seem to be strange!
Check them again. liftDir (0 0 1); dragDir (-1 0 0); You defined -x as the direction for the drag and +z for the lift. Are you sure about them? |
|
![]() |
![]() |
![]() |
![]() |
#4 | |
New Member
Juanito
Join Date: Oct 2010
Posts: 27
Rep Power: 16 ![]() |
Quote:
|
||
![]() |
![]() |
![]() |
![]() |
#5 |
New Member
Juanito
Join Date: Oct 2010
Posts: 27
Rep Power: 16 ![]() |
Thank you for your coment aut_iut, lift Dir was wrong because I did not want to know it and dragDir is ok because my magUInf is also negative.
|
|
![]() |
![]() |
![]() |
![]() |
#6 |
New Member
Esmaeil Ahmadiyan
Join Date: Sep 2011
Posts: 26
Rep Power: 15 ![]() |
||
![]() |
![]() |
![]() |
![]() |
#7 |
Member
Rasoul
Join Date: Feb 2010
Posts: 32
Rep Power: 16 ![]() |
Salam Esmaeil,
Could you let me know what kind of error you've got? regards, |
|
![]() |
![]() |
![]() |
![]() |
#8 |
New Member
Esmaeil Ahmadiyan
Join Date: Sep 2011
Posts: 26
Rep Power: 15 ![]() |
salam dear Rasoul
Tanks for your reply In fact I saw fallowing warning in log.dsmcfoam file FOAM Warning : From function void forces::read(const dictionary&) in file forces/forces.C at line 277 Could not find U, p in database. De-activating forces. best regardes |
|
![]() |
![]() |
![]() |
![]() |
#9 |
New Member
Esmaeil Ahmadiyan
Join Date: Sep 2011
Posts: 26
Rep Power: 15 ![]() |
of course I added the following lines in controlDict file
forceCoeffs1 { type forceCoeffs; functionObjectLibs ("libforces.so"); outputControl outputTime; //outputInterval 1; //outputControl timeStep; outputInterval 1; patches (obstacle); //change to your patch name pName p; UNmae U; log true; rhoName rhoInf; rhoInf 1.225; CofR (0 0 0); liftDir (0 1 0); dragDir (1 0 0); pitchAxis (0 0 0); magUInf 7600; lRef 2.5146; Aref 0.25146; } |
|
![]() |
![]() |
![]() |
![]() |
#10 |
Member
Rasoul
Join Date: Feb 2010
Posts: 32
Rep Power: 16 ![]() |
Hi Esmaeil,
It seems that the OpenFOAM can not find U and p files. Be sure that U and p files are available at 0 filder (initial conditions). Are you using the same name for your patch? I guess you need to change the name of the patch based on your case. By the way, you should have been added both forcecoeffs and forces at ControlDict file. Add this: functions ( forceCoeffs { type forceCoeffs; functionObjectLibs ("libforces.so"); //outputControl outputTime; //outputInterval 1; outputControl timeStep; outputInterval 1; patches (paredes); //change to your patch name rhoInf 1.225; CofR (0 0 0); liftDir (0 0 1); dragDir (-1 0 0); pitchAxis (0 0 0); magUInf -50; lRef 1; Aref 1; } forces { type forces; functionObjectLibs ("libforces.so"); // Lib to load //outputControl outputTime; //outputInterval 1; outputControl timeStep; outputInterval 10; patches (paredes); // change to your patch name rhoName rhoInf; rhoInf 1.225; // Reference density for fluid CofR (0 0 0); // Origin for moment calculations } If you have some difficulties send me your test case and I will take a look on it. regards, Rasoul |
|
![]() |
![]() |
![]() |
![]() |
#11 |
New Member
Esmaeil Ahmadiyan
Join Date: Sep 2011
Posts: 26
Rep Power: 15 ![]() |
Hi dear Rasoul
Thanks fr your suggestions There is no P and U files in 0 folder in dsmcfoam solver at all !!! What means of PatchName ? Best regards. |
|
![]() |
![]() |
![]() |
![]() |
#12 | |
New Member
Qiang Zhou
Join Date: May 2010
Location: Eindhoven University of Technology
Posts: 28
Rep Power: 16 ![]() |
Quote:
|
||
![]() |
![]() |
![]() |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
Setup/monitor points of pressure and force coefficients | siw | CFX | 3 | October 22, 2010 07:07 |
changing the coefficients of pressure correction | Noel | Phoenics | 1 | April 7, 2009 09:54 |
Correct lift but wrong pressure drag - possible? | zx | Main CFD Forum | 4 | July 28, 2007 00:38 |
Neumann pressure BC and velocity field | Antech | Main CFD Forum | 0 | April 25, 2006 03:15 |
About the pressure coefficients | Wong | Phoenics | 3 | June 11, 2003 17:15 |