# rotatingWallVelocity bc

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 September 9, 2010, 06:42 rotatingWallVelocity bc #1 New Member   Join Date: Jul 2009 Posts: 11 Rep Power: 16 Hi Foamers, i try to calculate a flow between two cylinders. The inner cylinder is rotating so i used the rotatingWallVelocity bc for the inner wall. My 0/U file: dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0 0); boundaryField { movingWall { type rotatingWallVelocity; origin (0 0 0); axis (0 0 1); omega 25; } fixedWall { type fixedValue; value uniform (0 0 0); } frontandback { type empty; } } Paraview shows that the rotating wall velocity is exact twice bigger then expected. The diameter of the inner cylinder is 0.035 m OpenFoam wall velocity 0.875 m/s. What is the unit of omega in the U ? Thanks an best regards Lodda

 September 9, 2010, 07:30 #2 Senior Member   Anonymous Join Date: Mar 2009 Posts: 110 Rep Power: 17 velocity (m/s) = omega (1/s) * radius (m) Are you using the cylinder diameter or the radius to compute the rotational velocity? That could be why your velocity is twice as big as you were expecting.

 September 9, 2010, 07:54 #3 New Member   Join Date: Jul 2009 Posts: 11 Rep Power: 16 The OpenFoam result for the rotating wall velocity is 0.875 m/s. I expected according to v = omega * r = 25 * 0.0175 = 0.4375 m/s. I dont know what is wrong. boundaryField { movingWall { type rotatingWallVelocity; origin (0 0 0); axis (0 0 1); omega 25; value nonuniform List 200 ( (0.0137422 -0.874784 0) (0.0412131 -0.873921 0) (0.0686432 -0.872195 1.86596e-27) (0.0960057 -0.869609 -0) (0.123273 -0.866164 0) (0.150419 -0.861864 0) This are the components of the calculated velocity. The magnitude at the rotating wall is always 0.875 m/s. Best regards Lodda

 September 9, 2010, 08:23 #4 Senior Member   Anonymous Join Date: Mar 2009 Posts: 110 Rep Power: 17 Ok, one thing to check (which I am sure you have done) is that the diameter you are using is correct. Second is to make sure your origin is in the right place. What am I looking at in the image? Do you have a cylinder within a cylinder? Apart from this, I'm a bit stumped tbh. I have it working without an issue on a more complex problem that this one.

 September 9, 2010, 08:33 #5 New Member   Join Date: Jul 2009 Posts: 11 Rep Power: 16 This are two cylinders and the inner cylinder is rotating with omega = 25 as explained above and thats it. Sorry, i checked my blockMeshdict the diameter is wrong! Thanks for answering

 September 9, 2010, 08:47 #6 Senior Member   Anonymous Join Date: Mar 2009 Posts: 110 Rep Power: 17 Heh, no worries. It's a surprisingly easy mistake to make!

 September 12, 2010, 02:41 #7 Member   David Join Date: Aug 2010 Location: North Ossetia, Vladikavkaz Posts: 30 Rep Power: 15 Lodda, I'm trying to simulate cylinder with rotating bottom, filled with a viscous laminar incompressible fluid. Your case is very similar to mine. Maybe you could send me your files, because I'm new to OpenFOAM, and can not figure out how I do it. Sorry for my English

 February 14, 2012, 07:53 train moving in tunnel #8 Member   Join Date: Jan 2012 Posts: 58 Rep Power: 14 hello , can any body help me as i am getting floating error: invalid number. my email sheikhnasir39@gmail.com with regards

June 18, 2018, 11:31
#9
Member

Viraj Belekar
Join Date: Jun 2016
Posts: 68
Rep Power: 9
Quote:
 Originally Posted by madad2005 Ok, one thing to check (which I am sure you have done) is that the diameter you are using is correct. Second is to make sure your origin is in the right place. What am I looking at in the image? Do you have a cylinder within a cylinder? Apart from this, I'm a bit stumped tbh. I have it working without an issue on a more complex problem that this one.
Greetings!

I am wanted ask to what do you mean by 'make sure your origin is in the right place'? I also have an annulus-type geometry in which the inner cylinder is rotating. Also, if we look at the source code:
const vectorField Up
(
(-om)*((patch().Cf() - origin_) ^ (axis_/mag(axis_)))
);

Shouldn't the distance be the perpendicular distance from the axis rather than the distance between the face center and the origin?

Thanks
Viraj