Defining porous media inside a domain

SH_P · May 3, 2012, 03:14

Hi guys,
Is it possible to define a sub-domain within our main flow domain and consider porosity only for that domain.
For example consider a cylinder in the flow, how can I define the cylinder in the flow to be porous? Can I still consider no-slip boundary condition (in direction tangent to the surface) for cylinder surface.

Lets give you a tangible example: assume that our cylinder is made of twisted coils, How can I simulate it in fluent?

Thanks for your help

t.krishnamohan · May 3, 2012, 04:08

You can create the spiral domain and define it/its surrounding as porous zone. But you cannot define no slip conditions as the porous zone is treated as fluid zone.

t.krishnamohan · May 3, 2012, 04:10

And for the cylindrical outer surface you can go with no slip boundary condition

SH_P · May 3, 2012, 04:15

Thanks for your answer Krishna,

I haven't simulated porous media before, so I didn't completely understand what you have said.
What do you mean by "Spiral domain"?
do you mean that I should define the volume inside the cylinder as porous domain and its surface as wall? Then how the fluid is supposed to enter the porous domain?

delaneyluke · May 3, 2012, 10:00

Hi Soroush
Your cylinder will be the porous domain. You don't need to model the spiral inside, but your resistance coefficients should be accurate to model it as a porous media. Alternately you could use a porous jump (2D plane) ONLY IF your resistance to flow is in the flow direction.

Your walls of the domain should be according to how the flow should enter. Those surfaces which allow flow are interiors and those that dont are walls.

Regards
Luke

SH_P · May 3, 2012, 10:14

Tahnks Luke,

So you're telling that the cylinder should be defined as porous domain and there is no need to define its boundaries (across the flow direction) separately?
Can resistance coefficients work to capture the real physic of the flow, I mean there should be a kind of no slip condition on the cylinder wall (although not like fully solid wall).

BTW, what is "spiral domain" any way?

Cheers,
>Soroush

delaneyluke · May 7, 2012, 03:17

The faces across the flow direction should be defined as interiors/interfaces.

Resistance can only capture the pressure drop and not the real flow physics since using the porous media model implies that you have simplified your geometry.

Spiral domain refers to the domain that contains the twisted coils you mentioned in your first post.

Regards
Luke

May 3, 2012, 03:14	Defining porous media inside a domain	#1
SH_P Member Soroush Join Date: Mar 2010 Posts: 52 Rep Power: 16	Hi guys, Is it possible to define a sub-domain within our main flow domain and consider porosity only for that domain. For example consider a cylinder in the flow, how can I define the cylinder in the flow to be porous? Can I still consider no-slip boundary condition (in direction tangent to the surface) for cylinder surface. Lets give you a tangible example: assume that our cylinder is made of twisted coils, How can I simulate it in fluent? Thanks for your help

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May 3, 2012, 04:08		#2
t.krishnamohan Member Krishna Join Date: Oct 2009 Posts: 34 Rep Power: 17	You can create the spiral domain and define it/its surrounding as porous zone. But you cannot define no slip conditions as the porous zone is treated as fluid zone.

May 3, 2012, 04:10		#3
t.krishnamohan Member Krishna Join Date: Oct 2009 Posts: 34 Rep Power: 17	And for the cylindrical outer surface you can go with no slip boundary condition

May 3, 2012, 04:15		#4
SH_P Member Soroush Join Date: Mar 2010 Posts: 52 Rep Power: 16	Thanks for your answer Krishna, I haven't simulated porous media before, so I didn't completely understand what you have said. What do you mean by "Spiral domain"? do you mean that I should define the volume inside the cylinder as porous domain and its surface as wall? Then how the fluid is supposed to enter the porous domain?

May 3, 2012, 10:00		#5
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	Hi Soroush Your cylinder will be the porous domain. You don't need to model the spiral inside, but your resistance coefficients should be accurate to model it as a porous media. Alternately you could use a porous jump (2D plane) ONLY IF your resistance to flow is in the flow direction. Your walls of the domain should be according to how the flow should enter. Those surfaces which allow flow are interiors and those that dont are walls. Regards Luke

May 3, 2012, 10:14		#6
SH_P Member Soroush Join Date: Mar 2010 Posts: 52 Rep Power: 16	Tahnks Luke, So you're telling that the cylinder should be defined as porous domain and there is no need to define its boundaries (across the flow direction) separately? Can resistance coefficients work to capture the real physic of the flow, I mean there should be a kind of no slip condition on the cylinder wall (although not like fully solid wall). BTW, what is "spiral domain" any way? Cheers, >Soroush

May 7, 2012, 03:17		#7
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	The faces across the flow direction should be defined as interiors/interfaces. Resistance can only capture the pressure drop and not the real flow physics since using the porous media model implies that you have simplified your geometry. Spiral domain refers to the domain that contains the twisted coils you mentioned in your first post. Regards Luke