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-   -   Confusion between 'non-slip' and 'slip' B.C (http://www.cfd-online.com/Forums/main/14896-confusion-between-non-slip-slip-b-c.html)

jinwon park March 5, 2008 09:30

Confusion between 'non-slip' and 'slip' B.C
 
For non-slip B.C, the velocities u and v are set zero. For slip B.C, the velocity u(assumed as the normal velocity) is only set zero. Is the solid wall in physics modeled by which one? Ideally, the fluid flow does not penetrate the wall and the tangential velocity may not be disappeared. In these cases, we can say that the wall is a slip-boundary condition. I would like to ask you all about the distintion between the use of 'non-slip B.C and 'slip B.C'. The objective of this equation is to find out the way to implement the solid wall in 2-D compressible flow simulations. Thanks in advance!

john March 5, 2008 09:50

Re: Confusion between 'non-slip' and 'slip' B.C
 
> For slip B.C, the velocity u(assumed as the normal velocity) is only set zero.

wrong, this is non-penetrating bc which is applied for every rigid walls. Normal component of velocity on wall is zero, U.n = 0

but for slip/no-slip bc, we work on tangential component of velocity vector, for no slip we have zero tangential volocity and for slip bc we have zero derivative of tangential velocity.

If you work with a coarse mesh, so your boundary layer (near wall) is not resolved due to coarse mesh, slip bc is more feasible.


jinwon park March 5, 2008 09:54

Re: Confusion between 'non-slip' and 'slip' B.C
 
If so, when are you using the non-slip B.C to impose the solid wall? Is there any case where the no slip B.C is properly applied?

ag March 5, 2008 10:01

Re: Confusion between 'non-slip' and 'slip' B.C
 
No-slip is applied to solid boundaries in viscous flow. It actually imposes a continuity of velocity at the boundary. If the boundary is moving then fluid particles at the surface take on the velocity of the surface. If the surface is not moving then the fluid velocity at the surface is zero.

jinwon park March 5, 2008 10:02

Re: Confusion between 'non-slip' and 'slip' B.C
 
I am solving compressible inviscid flows. Is it applicable to my cases as well?

ag March 5, 2008 12:07

Re: Confusion between 'non-slip' and 'slip' B.C
 
If you are solving the inviscid (Euler) equations then the slip wall condition is the appropriate condition to apply.

jinwon park March 5, 2008 12:27

Re: Confusion between 'non-slip' and 'slip' B.C
 
Thanks ag!

Tom March 6, 2008 05:56

Re: Confusion between 'non-slip' and 'slip' B.C
 
Actually for an inviscid fluid the only boundary condition you should be applying is no flow normal to the surface. The no-slip condition arises in a viscous fluid because the equations are higher-order and so need additional boundary conditions.


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