coeff of drag and lift on cylinder
 

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.

Dear Malhar
try to see only cl in your visualizer. because it maybe have small fluctuations in comparing to cd.

..
 

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:confused:..

thanks n regards,
malhar

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.

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.

controldict
 

/*--------------------------------*- 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;
}
);

// ************************************************** *********************** //

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.

forcesCoeffs around a circular cylinder
 

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

lift and drage problem
 

Dear Alireza
plz copy your control dict to post. your problem is maybe in control dict firstly

dear niaz
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;
}

);



// ************************************************** *********************** //

OMG i undrestand my big mistake, i didn't change the magUinfo and yes it is the problem :) thank u so much :)

Problems getting Forces folder
 

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 (non-dimensional forces with 0.5rhoU2ArefLRef)
Aref 1; //reference length scale for moment calculations (non-dimensional forces with 0.5rhoU2Aref)
}


}


// ************************************************** *********************** //