# Rotating cylinder

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 April 7, 2009, 04:14 Rotating cylinder #1 New Member   Laurent Beaudet Join Date: Mar 2009 Posts: 9 Rep Power: 9 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

 April 7, 2009, 05:52 #2 New Member   Laurent Beaudet Join Date: Mar 2009 Posts: 9 Rep Power: 9 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?

 April 7, 2009, 09:55 #3 New Member   Laurent Beaudet Join Date: Mar 2009 Posts: 9 Rep Power: 9 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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