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June 14, 2012, 10:21 
coeff of drag and lift on cylinder

#1 
New Member
Malhar Malushte
Join Date: May 2012
Posts: 16
Rep Power: 6 
hello everyone,
i am trying to study the flow across the stationary. rotating, osillating cylinder in a confined channel. i have simulated some flows. i am trying to calculate the drag and lift forces and their coeffs on the cylinder. i got values for Cd, Cl., but Cl seems to be constant for each time step, whereas the force is fluctuating w.r.t to vortex shedding. please help me through this. thanks n regards, Malhar. 

June 14, 2012, 11:38 

#2 
Senior Member
A_R
Join Date: Jun 2009
Posts: 120
Rep Power: 9 
Dear Malhar
try to see only cl in your visualizer. because it maybe have small fluctuations in comparing to cd. 

June 14, 2012, 12:22 
..

#3 
New Member
Malhar Malushte
Join Date: May 2012
Posts: 16
Rep Power: 6 
dear Niaz,
thanks for replying... well i am new to of. dont even know wat a visualizer is! and if the values are seen for non rotating cylinder at Re=100, the Cl varies from 0.39 to 0.42. correct me if am wrong in next stmt. if the lift forces fluctuate w.r.t to vortex sheds, once +ve n once _ve in cylce den should nt the Cl also be +ve and ve??? dat is my big worry.. Cl is constantly ve varying from 0.39 to 0.42 pls guide me.. thanks n regards, malhar 

June 14, 2012, 15:34 

#4 
Senior Member
A_R
Join Date: Jun 2009
Posts: 120
Rep Power: 9 
Dear Malhar
visualizer is soft such as tecplot. now, ofcourse it is not correct. it seems that your solution is not converged(it happens when you import mesh from another mesh generator such as gambit) just in fvsolution increase the ncorrectors to correct it. you can load your test case if you need more info. 

June 15, 2012, 01:27 

#5 
New Member
Malhar Malushte
Join Date: May 2012
Posts: 16
Rep Power: 6 
Dear Niaz,
once again thanks for the reply. solution not converged means do you want to say that my mesh is coarse??? or it has not reached a steady state??? what does increasing ncorrectors in fvsolution mean ??? i try going in the fvsolution directory. pls tel me any way for understanding the codes in OF and its structure. also i wil post here the control dict i have included in mycase. thanks n regards, malhar. 

June 15, 2012, 01:35 
controldict

#6 
New Member
Malhar Malushte
Join Date: May 2012
Posts: 16
Rep Power: 6 
/** C++ **\
 =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 2.1.0   \\ / A nd  Web: www.OpenFOAM.org   \\/ M anipulation   \**/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object controlDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // application icoFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 200; deltaT 0.01; writeControl timeStep; writeInterval 50; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true; functions ( forces { type forces; functionObjectLibs ("libforces.so"); patches (cylinder); pName p; UName U; rhoName rhoInf; rhoInf 1000; // Reference density, fluid CofR (2.5 0 0); // Origin for moment calculations outputControl timeStep; outputInterval 50; } forceCoeffs { type forceCoeffs; functionObjectLibs ("libforces.so"); patches (cylinder); // pName p; // UName U; rhoName rhoInf; rhoInf 1000; CofR (2.5 0 0); liftDir (2.5 0.5 0); dragDir (2 0 0); pitchAxis (2.5 0 0); magUInf 1; // Free stream velocity lRef 1; // Diameter of cylinder? Aref 3.142; // Ref. Area = cross sectional area? outputControl timeStep; outputInterval 50; } ); // ************************************************** *********************** // 

February 11, 2014, 11:35 

#7 
Senior Member
ok
Join Date: Oct 2013
Posts: 339
Rep Power: 6 
Dear Malhar,
did you fix your problem? I'm working in something which is very close to your case. If you get your result, could you please provide me all steps that you did. I mean, what solver you used? What is blockMeshDict, controlDict, and all important files that you made changes on them? Many thanks for your help. 

May 28, 2014, 04:14 
forcesCoeffs around a circular cylinder

#8 
New Member
Alireza Heidari
Join Date: Apr 2014
Posts: 5
Rep Power: 4 
Hello dear Foamers
i'm new to openFoam and trying to calculate lift and drag coeffs around a fixed circular cylinder using codes in controlDict, i attain different result for a specific Re number (Re=200) when i change the diameter of the cylinder... solver: icoFoam first case: d=0.025 u=0.008032 nu=1.004*10^6 ===> Re=200 second case: d=0.0375 u=0.005355 nu=1.004*10^6 ===> Re=200 for the first case the lift coeffs amplitude is (1.3  1.3) for the second one is between (0.57  0.57) while according to papers it should be between (0.7  0.7) thanks and regards Alireza Heidari 

May 28, 2014, 06:31 
lift and drage problem

#9  
Senior Member
A_R
Join Date: Jun 2009
Posts: 120
Rep Power: 9 
Quote:
Dear Alireza plz copy your control dict to post. your problem is maybe in control dict firstly 

May 28, 2014, 07:24 

#10  
New Member
Alireza Heidari
Join Date: Apr 2014
Posts: 5
Rep Power: 4 
Quote:
thank you so much for your instant reply /** C++ **\  =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 1.5   \\ / A nd  Web: http://www.OpenFOAM.org   \\/ M anipulation   \**/ FoamFile { version 2.0; format ascii; class dictionary; object controlDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // application icoFoam; startFrom latestTime; startTime 0; stopAt endTime; endTime 600; deltaT 0.02; writeControl timeStep; writeInterval 100; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression uncompressed; timeFormat general; timePrecision 6; runTimeModifiable yes; functions ( forces { type forces; enabled true; functionObjectLibs ("libforces.so"); //Lib to load patches ("cylinder"); // change to your patch name pName p; UName U; rhoName rhoInf; rhoInf 1.0; //Reference density for fluid CofR (0 0 0); //Origin for moment calculations outputControl timeStep; outputInterval 5; } forceCoeffs { type forceCoeffs; enabled true; functionObjectLibs ("libforces.so"); patches ("cylinder"); //change to your patch name pName p; UName U; rhoName rhoInf; rhoInf 997; CofR (0 0 0); liftDir (0 1 0); dragDir (1 0 0); pitchAxis (0 0 0); magUInf 0.006; lRef 0.024186; Aref 0.000906975; outputControl timeStep; outputInterval 5; } ); // ************************************************** *********************** // 

May 28, 2014, 07:37 

#11 
New Member
Alireza Heidari
Join Date: Apr 2014
Posts: 5
Rep Power: 4 

June 30, 2014, 13:23 
Problems getting Forces folder

#12 
New Member
JUAN DAVID OSORIO
Join Date: Jun 2014
Posts: 1
Rep Power: 0 
Hello everyone,
I'm trying to calculate the forces on a complex mesh (corals), however the only folder that I'm getting is for forceCoeffs. This is the ContolDict file. Am I doing somethign wrong? please help me through this. Best regards, Juan David /** C++ **\  =========    \\ / F ield  OpenFOAM: The Open Source CFD Toolbox   \\ / O peration  Version: 2.1.0   \\ / A nd  Web: www.OpenFOAM.org   \\/ M anipulation   \**/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object controlDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // application waveFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 20; deltaT 0.001; writeControl adjustableRunTime; writeInterval 0.01; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression uncompressed; timeFormat general; timePrecision 6; runTimeModifiable yes; adjustTimeStep yes; maxCo 0.8; maxAlphaCo 0.8; maxDeltaT 0.001; libs ( "libOpenFOAM.so" "libincompressibleRASModels.so" "libfvMotionSolvers.so" "libforces.so" ); functions { forces //nombre que sea, se puede copiar varias veces { type forces; functionObjectLibs ("libforces.so"); outputControl timeStep; // runTime outputInterval 1; // 0.01 patches ("palmata_ExportedfromBlender"); pName p; //could be p or p_rgh UName U; rhoName rhoInf; log true; CofR (0 0 0.03); rhoInf 1000; } forceCoeffs { type forceCoeffs; functionObjectLibs ( "libforces.so" ); outputControl timeStep; outputInterval 1; patches ( "palmata_ExportedfromBlender" ); pName p; UName U; rhoName rhoInf; log true; liftDir (0 0 1); dragDir (1 0 0); CofR (0 0 0.052); //Axle midpoint on ground pitchAxis (0 1 0); //Pitch axis for moment magUInf 1; rhoInf 1000; lRef 1; //reference length scale for moment calculations (nondimensional forces with 0.5rhoU2ArefLRef) Aref 1; //reference length scale for moment calculations (nondimensional forces with 0.5rhoU2Aref) } } // ************************************************** *********************** // 

Tags 
cylinder, drag, lift, openfoam 2.1.0 
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