I am trying to understand the no slip condition (parallel velocity =0) in the presence of a permeable surface (in this case a Reverse Osmosis filter mesh ). Does the presence of permeability affect the no slip condition ? Intuitively For a gas Where viscous effects are dominated by momentum gradients and molecular surface roughness . I can see permeability (above the mean free path nm scale) affect the no slip condition as the molecules will not interact with the surface (pass thru the permeable sections ) maintaining there average momentum. For a liquid I see the no slip condition holding at much greater scales (perhaps mm) as the forces of cohesion and adhesion dominate liquid viscosity and will affect average momentum (reducing to 0 ) over a much greater scale. To me this suggests a scale limit to permeability for both Gas and Liquid scenarios before the no slip assumption is affected How can I quantify or test this . I cannot find anything that deals with this in my searching?