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non-null velocity at walls despite noSlip condition

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Old   December 31, 2016, 05:41
Question non-null velocity at walls despite noSlip condition
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Jay B.
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Hi all!

It's all in the title.

- OF version: v1606+
- solver: simpleFoam
- general problem description: "quick and dirty" laminar flow simulation with stream wise flow periodicity and symmetry BCs on the model boundaries which are not cyclic or walls.

The mesh and other numerical settings might not be optimal, but the simulation runs smoothly and with 20 layers of elements across the domain (10 in the model, x2 due to symmetry BC), I would expect the zero velocity condition at the walls to be enforced without a problem.

I attach here the complete setup, minus the Gmsh-generated mesh file (too big). Also, a screen capture of the velocity at the walls, which will give you a good idea of what the missing mesh looks like.

Basically, the velocity field at the wall in the xy-plane is almost identical to the one on the symmetry plane 10 prism layers away...

Any clue?
Attached Files
File Type: zip periodicity_streamwise_simpleFoam.zip (77.1 KB, 2 views)
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Old   December 31, 2016, 07:20
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Jay B.
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I've switched the initial condition at the walls from noSlip to fixedValue, and this enforced zero velocity successfully.

Apparently the noSlip condition is new, and is supposed to be equivalent to fixedValue with a value of (0 0 0):
https://github.com/OpenFOAM/OpenFOAM...98d0b13f22b515

Maybe a bug?
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Old   September 13, 2017, 02:37
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Ben
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Hi, although late, are you able to confirm this? I've been using the noSlip condition for U at my wing wall I'm still getting nonzero values for the surface velocities.

edit: i'm guessing there's something to do with how the data is viewed from paraview as well? I'm unsure about this. Hoping someone could enlighten!
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Old   December 15, 2017, 09:48
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I'm also experiencing non-zero velocities at my noSlip boundaries (when viewed in paraview). Might this be due to the mapping from cells to faces? The velocity in the cell center of the boundary cells is not equal to zero, I guess, and mapping or interpolating this value to the face may lead to non-zero wall velocities. Is there a way to access the face values?
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