# OpenFOAM Variable Velocity Boundary Conditions

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 May 18, 2011, 10:31 OpenFOAM Variable Velocity Boundary Conditions #1 Member   Nickolas P Join Date: Oct 2010 Location: Greece Posts: 30 Rep Power: 8 Hello everybody, I m kind of new to the OpenFOAM package but I try to learn as much as I can and have run half a dozen of cases with simple geometries and boundary conditions. Actually, I would like to ask if anybody can give me some info on how to implement boundary conditions (especially the velocity) that vary acoording to the geometry of the mesh. Actually, I study the flow region between two cylindrical rollers to a very close distance each other (actually a few mm). I understand the concept of declaring the patches of the generated mesh as well as the boundary conditions for P and U files. For this problem, however, the velocity boundary condition that belong to the declared patches of the surface of the cylinders varies as the tangential velocity of the cylinders changers direction as they roll. In the U file the boundary condition can be declared as I see by: (ux, uy, uz). In my problem, the tangential velocity, say V is: V = SQRT (ux^2+uy^2). At the circumference of the cylinders the V vector is always the same regarding its "meter", but changes direction due to the different values of ux and uy as we move along the circumference. My question is how that different values of ux and uy that change from position to position of the cylinder's circumference can be implemented as velocity boundary conditions of the declared patches (actually for only a part of the surface of the cylinders). Any help would be greatly appreciated. Thanks a lot in advance. Nickolas

 May 19, 2011, 03:18 rotating Wall #2 New Member   mohsen cheraghi Join Date: Jun 2010 Location: Switzerland Posts: 27 Rep Power: 8 Hi You can try rotatingWallVelocity boundary condition. I used it for a cylinder and it works. good luck

 May 19, 2011, 05:37 #3 Member   Nickolas P Join Date: Oct 2010 Location: Greece Posts: 30 Rep Power: 8 Hello, Yes, thanks for your help. I found the following last night and implement it and actually works fine! type rotatingWallVelocity; origin (0 0.2 0); axis (0 0 1); omega 10; raj kumar saini likes this.

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