The velocity of wall boundary condtion
 

hello everyone:
There is a problem puzzzing me several days.
As we know, the tangent velocity of wall boundary condition equal zero . how is the normal velocity.
Does the normal velocity adopt velocity gradient equalling zero (that is to say the wall normal velocity equall the velocity of cell adjant to wall )or velocity value equalling zero ?

Hi,

If the wall is a non-slip, non-porous wall, then both tangential and normal velocity of the fluid adjacent to the wall is equal to that of the wall (if the wall is stationary, those two components are zero).

for a stationary wall: if the wall is a free-slip wall, then tangential velocity can be non-zero, and if the wall is porous, then normal velocity can be non-zero.

I hope this is what you wanted to know.