Reply To: Applying a friction value to non-slip boundary condition
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we don’t currently have (partial-)slip treatment for boundaries other than axis-aligned or 45 deg walls – this is not an option for a pipe geometry.
But even with no-slip walls you actually account for some roughness coefficient known as hydraulically smooth.
You can calculate a present coefficient from the wall shear stress in your simulation.
Usually we can neglect additional friction from the material as viscous effects dominate over the entire diameter in the laminar pipe flow.
Therefore, we only have a very small influence of the relative roughness on the pressure drop.
Roughness gains importance in micro-channels or turbulent flow where the viscous sublayer is much smaller.
In such cases we underestimate the dissipation rate in the viscous sublayer and need modelling of friction effects near the wall.
I agree with you that higher gradients due to partial slip boundaries would increase the wall shear stress and the roughness coefficient.
Maybe you can define a velocity on the first fluid layer beyond the no-slip wall to artificially increase the tangential velocity components for a higher wall shear stress.
Hope this helps!