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Old   June 18, 2012, 01:48
Default slip wall boundary condition
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Mehdi
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Hi everyone
I read an article and there is mention slip wall boundary condition for far-field and is said it equals wall shear=0.
Can anyone explain what it means and what is differences between slip wall boundary and symmetry?

thanks so much
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Old   June 18, 2012, 05:55
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Hi mb.pejvak,
Slip condition refers to a surface where effect of shear stress is considers zero. In case of symmetric bodies we cut down the geometry to half to reduce computation size, memory and time. So the surface corresponding to cutting pane is called symmetry. Once done with the simulation of semi body a mirror option is used to create the another half.


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Old   June 18, 2012, 21:37
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I know what you mean, but my problem is I can't find out what is differences between them in applying.
if we assume a dummy cell and named it 0 and cell near it in domain named 1:
in symmetric plane we apply U0=U1
and in slip wall also apply the same.
am I wrong?
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Old   June 18, 2012, 23:22
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In general, slip and symmetry are much the same, if not exactly the same. But, sometimes it is implementation dependent. For example one could have p(-1)=p(1) for symmetry but p(0)=p(1) for wall. Also, the turbulence model boundary conditions could be different. OK, I don't know what it means to have a slip turbulence model, but I guess that depends on what someone is trying to do. Also, a turbulence model could depend on the distance from a surface. So it's possible that setting a far field condition to a wall will affect the turbulence model.

But, the answer, to first order, is that they are the same.
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Old   May 22, 2014, 04:49
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Quote:
Originally Posted by Martin Hegedus View Post
In general, slip and symmetry are much the same, if not exactly the same. But, sometimes it is implementation dependent. For example one could have p(-1)=p(1) for symmetry but p(0)=p(1) for wall. Also, the turbulence model boundary conditions could be different. OK, I don't know what it means to have a slip turbulence model, but I guess that depends on what someone is trying to do. Also, a turbulence model could depend on the distance from a surface. So it's possible that setting a far field condition to a wall will affect the turbulence model.

But, the answer, to first order, is that they are the same.
Hi

as far as I know, free slip condition is based on zero shear stress and stationary wall

How about in case of moving wall and zero shear stress? I guess the velocity of moving wall will determine the velocity of cell next to the wall

Is it right?
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Old   May 24, 2014, 06:49
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Quote:
Originally Posted by mb.pejvak View Post
Hi everyone
I read an article and there is mention slip wall boundary condition for far-field and is said it equals wall shear=0.
Can anyone explain what it means and what is differences between slip wall boundary and symmetry?

thanks so much
Hi Pejvak,

1. I don't know the relationship between your first sentence and the second.
2. The slip wall boundary I know, occurs when the local Kn number is high enough to cause slip velocity existence. The slip velocity is no zero but it does not mean wall shear is zero.
3. While for symmetry boundary condition, the shear stress is considered zero at the symmetry line.

Cheers,
Shawn
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