Boundary Conditions on a Sphere

VSass · December 6, 2012, 06:34

Pals,

i want to apply a BC for velocity on a sphere. I want the velocity ALWAYS to be tangent on the faces of the sphere and never,during the solution, going through its surface.

Does anybody know which BC i should apply?

tomf · December 7, 2012, 04:42

Hello VSass,

It depends whether your sphere should be moving (movingMesh) or if it is only rotating in a stationary point. I am assuming it is the latter, in that case you can use:

rotatingWallVelocity

If it is the former:

movingWallVelocity

Depending on the choice you may need to set some other parameters that describe the motion.

Regards,
Tom

VSass · December 7, 2012, 04:47

Thanks Tomf,

i have a fixed sphere so i guess i sould work with the rotatingWallVelocity.

Good day to you

Bernhard · December 7, 2012, 07:44

I am not sure what you are trying to model, but you could also consider slip as boundary condition.

VSass · December 7, 2012, 10:46

Bernhard,

i have a hybrid sphere seperated in two boundaries, upstream and downstream, and this hybrid sphere is located inside a farfield which is also spherical and we suppose it is far away from our hybrid sphere. I am trying to solve the Navier - Stokes equations in the hybrid sphere using icoFoam,but Courant number keeps crashing no matter what time step i apply. I now work on modified icoFoam in order to keep e.g. maxCo=0.7,but i want to be sure that the crash is not due to boundary conditions.

December 6, 2012, 06:34	Boundary Conditions on a Sphere	#1
VSass Member VS Join Date: Nov 2012 Posts: 86 Rep Power: 14	Pals, i want to apply a BC for velocity on a sphere. I want the velocity ALWAYS to be tangent on the faces of the sphere and never,during the solution, going through its surface. Does anybody know which BC i should apply?

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December 7, 2012, 04:42		#2
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 647 Rep Power: 32	Hello VSass, It depends whether your sphere should be moving (movingMesh) or if it is only rotating in a stationary point. I am assuming it is the latter, in that case you can use: rotatingWallVelocity If it is the former: movingWallVelocity Depending on the choice you may need to set some other parameters that describe the motion. Regards, Tom

December 7, 2012, 04:47		#3
VSass Member VS Join Date: Nov 2012 Posts: 86 Rep Power: 14	Thanks Tomf, i have a fixed sphere so i guess i sould work with the rotatingWallVelocity. Good day to you

December 7, 2012, 07:44		#4
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 22	I am not sure what you are trying to model, but you could also consider slip as boundary condition.

December 7, 2012, 10:46		#5
VSass Member VS Join Date: Nov 2012 Posts: 86 Rep Power: 14	Bernhard, i have a hybrid sphere seperated in two boundaries, upstream and downstream, and this hybrid sphere is located inside a farfield which is also spherical and we suppose it is far away from our hybrid sphere. I am trying to solve the Navier - Stokes equations in the hybrid sphere using icoFoam,but Courant number keeps crashing no matter what time step i apply. I now work on modified icoFoam in order to keep e.g. maxCo=0.7,but i want to be sure that the crash is not due to boundary conditions.