Solve equation in subregion of geometry

Dharoc · December 3, 2017, 14:00

Hello,

I am interested in studying the viscous sublayer next to a wall in an incompressible fluid flow. More precisely, I would like to calculate the fluid velocity field for a geometry and then solve an equation the depends on said velocity field in a small subregion of the geometry, the volume next to a specific face.

Calculating the flow field is not an issue. The problem is that I do not know how to approach the second part, solving an equation in a subregion, so I am asking for some advice that can point me in the right direction.

The only thing I have found so far is the following topic by chriss85.

His approach, by using extrudeToRegionMesh, unfortunatly does not work in my case as it creates two separate regions. As far as I understand it is not possible to couple the two regions and solve fluid flow in both (i.e. to let the fluid flow between the two regions as if the boundary between the regions were not there). Is there a way around this that I am not aware of, or is there always a "hard boundary" between two regions?

A second approach would be to calculate the fluid flow in the entire geometry and then solve the equation as a part of the post-processing. The leads to the problem of how one would define the boundary conditions if there is not a face to attatch it to. Adding a face creates the same problems as the first approach. Is it possible to programatically create a field in a subsection of the geometry and boundary conditions not attatched to a face?

I hope I have made myself clear. If not, please comment on what's unclear and I'll expand on it.

Thanks in advance

Dharoc · December 9, 2017, 05:03

I think I may have figured out a way to get this to work using the MapFields utility.

1: Calculate the fluid velocity field for the entire geometry.
2: Define the geometry for the subregion.
3: Map part of the fluid velocity field on to the subregion using MapFields.
4: Set up boundary condition, et.c. and solve the second equation on the second geometry.

December 3, 2017, 14:00	Solve equation in subregion of geometry	#1
Dharoc New Member Albin Lindskog Join Date: Dec 2017 Posts: 8 Rep Power: 8	Hello, I am interested in studying the viscous sublayer next to a wall in an incompressible fluid flow. More precisely, I would like to calculate the fluid velocity field for a geometry and then solve an equation the depends on said velocity field in a small subregion of the geometry, the volume next to a specific face. Calculating the flow field is not an issue. The problem is that I do not know how to approach the second part, solving an equation in a subregion, so I am asking for some advice that can point me in the right direction. The only thing I have found so far is the following topic by chriss85. His approach, by using extrudeToRegionMesh, unfortunatly does not work in my case as it creates two separate regions. As far as I understand it is not possible to couple the two regions and solve fluid flow in both (i.e. to let the fluid flow between the two regions as if the boundary between the regions were not there). Is there a way around this that I am not aware of, or is there always a "hard boundary" between two regions? A second approach would be to calculate the fluid flow in the entire geometry and then solve the equation as a part of the post-processing. The leads to the problem of how one would define the boundary conditions if there is not a face to attatch it to. Adding a face creates the same problems as the first approach. Is it possible to programatically create a field in a subsection of the geometry and boundary conditions not attatched to a face? I hope I have made myself clear. If not, please comment on what's unclear and I'll expand on it. Thanks in advance

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December 9, 2017, 05:03		#2
Dharoc New Member Albin Lindskog Join Date: Dec 2017 Posts: 8 Rep Power: 8	I think I may have figured out a way to get this to work using the MapFields utility. 1: Calculate the fluid velocity field for the entire geometry. 2: Define the geometry for the subregion. 3: Map part of the fluid velocity field on to the subregion using MapFields. 4: Set up boundary condition, et.c. and solve the second equation on the second geometry.