Custom boundary condition

andreanedl · November 3, 2016, 13:23

Hi,

I need to modify a no slip wall boundary condition:

Wall :
Fluid normal (z-) velocity component = 0
No slip :
Fluid tangential (x and y) velocity = wall velocity

Custom part :
Fluid velocity in the z+ direction = 0
***Adding this part in a boundary condition is what I’m looking for***

Do someone know how to create a custom boundary condition on CFX?

ghorrocks · November 3, 2016, 16:18

I do not understand what is different about your proposed boundary condition and the standard no-slip condition. The standard no-slip condition imposes fluid velocity normal to the wall = 0 as well.

andreanedl · November 3, 2016, 16:28

If all components of the fluid velocity are 0, how can this droplet move on a no slip wall? (https://youtu.be/XybHyC6Vbls)

ghorrocks · November 3, 2016, 16:34

Excellent question!

This is actually one of the key limitations of the Navier Stokes equations with VOF modelling and is the subject of research. Shikhmurzaev is one of the leading researchers in this field.

There are no simple answers to this issue and certainly no CFD code I am aware of has a physically correct model for moving contact lines.

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November 3, 2016, 16:18		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,728 Rep Power: 143	I do not understand what is different about your proposed boundary condition and the standard no-slip condition. The standard no-slip condition imposes fluid velocity normal to the wall = 0 as well.

November 3, 2016, 16:28		#3
andreanedl New Member andreanedl Join Date: Nov 2016 Posts: 2 Rep Power: 0	If all components of the fluid velocity are 0, how can this droplet move on a no slip wall? (https://youtu.be/XybHyC6Vbls)

November 3, 2016, 16:34		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,728 Rep Power: 143	Excellent question! This is actually one of the key limitations of the Navier Stokes equations with VOF modelling and is the subject of research. Shikhmurzaev is one of the leading researchers in this field. There are no simple answers to this issue and certainly no CFD code I am aware of has a physically correct model for moving contact lines.