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Old   April 7, 2009, 04:14
Default Rotating cylinder
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Laurent Beaudet
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Dear all,

I try to simulate flow over a rotating cylinder with GGI, but I still have problems.
For laminar flows, the vortex shedding only depends on 2 parameters:
- Re, the Reynolds number (d being the diameter of the cylinder and U the upstream velocity, Re=d*U/nu...)
- alpha, the dimensionless peripheral velocity (the ratio of the cylinder’s peripheral speed to the speed of the flow, alpha=(d*pi*rpm)/(60*U)...)

I am surprised to get different results when I use the same set of parameters (Re=200 & alpha=1.5) but different values of upstream velocities, of diameters, of rounds per minute.
For example, if instead of (d=0.1 m, U=0.03 m, rpm=8.594368715 rpm), I use (10*d, U/10, rpm/100), flows are far different. But Re and alpha are the same, so results should be the same.

The input files include:

- in 0/U:
inlet
{
type fixedValue;
value uniform (0.03 0 0); //or 0.03/10=0.003
}

- in constant/polyMesh/blockMeshDict:
convertToMeters 0.1; //or 0.1*10=1
vertices
(
(0 -0.5 0) //cylinder
(0.5 0 0) //cylinder
(0 0.5 0) //cylinder
(-0.5 0 0) //cylinder
(...)

- in constant/dynamicMeshDict:
mixerGgiFvMeshCoeffs
{
coordinateSystem
{
type cylindrical;
origin (0 0 0);
axis (0 0 1);
direction (1 0 0);
}
rpm 8.594368715; //or 0.08594368715
}

- in system/controlDict:
applicationClass icoTopoFoam;
(...)
functions
(
forceCoeffs
{
type forceCoeffs;
functionObjectLibs (“libforces.so”);
patches (cylinder);
rhoInf 1.225;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 0.03; //or 0.003
lRef 0.1; //or 1
Aref 0.01; //or 1
}
);

Tell me where I’m wrong! Where could be the mistake? Tell me things I should try to solve this problem...
If you need any further detail, just ask.

Regards,
Laurent
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Old   April 7, 2009, 05:52
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Laurent Beaudet
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Is there a way to check the Reynolds number?

Maybe I am not in the conditions I expect...
I think I study Re=200, but it's perhaps not the case?
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Old   April 7, 2009, 09:55
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Laurent Beaudet
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I think I have the answer.
I was actually not at the same Reynolds number. Indeed, I made a mistake that hopefully I've solved.
Sorry for making a new thread for nothing...
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