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-   -   porous bed (http://www.cfd-online.com/Forums/fluent/105157-porous-bed.html)

kuldeep.vit July 24, 2012 07:18

porous bed
 
hello,

i am modelling the flow of fluid through a porous media.

can anyone tell how to define a part of cylindrical bed as porous, and what are the boundary conditions...???

thanking you.

kuldeep.vit July 24, 2012 07:21

Quote:

Originally Posted by kuldeep.vit (Post 373199)
hello,

i am modelling the flow of fluid through a porous media.

can anyone tell how to define a part of cylindrical bed as porous, and what are the boundary conditions...???

thanking you.

please help..

rwryne July 24, 2012 09:33

You aren't getting any help because a) this is the wrong subforum, b) you didnt specify any software.

Give a lot mroe info and you're more likely to get help. Moving this to general for now

kuldeep.vit July 24, 2012 11:18

i am using gambit 2.4 and fluent 6.3...

mettler July 24, 2012 16:12

fluent has a whole section on how to model porous media. If you read thru it you might find a lot of answers to your questions. Also, do a search in this forum. This topic has been covered quite a bit, and that might help too. It is not too difficult. good luck

kuldeep.vit July 25, 2012 02:36

i have gone through the tutorial and tried doing but the final profile i am getting is wrong.

since its a porous bed there must be some dispersion but the profile i am getting is like a slug flow within 1 min.

mettler July 25, 2012 09:08

slug flow is the correct velocity profile for porous media.

kuldeep.vit July 25, 2012 10:54

thanx for the reply,

but the profile is not changing by changing the inlet velocity, and within 1 min fluidd flows from inlet to outlet but theoretically it should take 20 mins.

mettler July 25, 2012 11:00

velocity profile is not changing? It is not going to change.. plug flow is plug flow. your pressure drop probably changes a good bit. There are some really good papers written about flow through porous media - they discuss plug flow as well. Jiang, Vafai, whitaker, Zhang are a few good ones

kuldeep.vit July 26, 2012 03:57

I really appreciate your time and effort for responding to my queries.

However, I would like to clarify certain points.
a) the velocity profile is plug flow, and I am obviously getting that, but the point is, the fluid is expected to disperse in the radial cross-section of the bed on changing the inlet velocity, which I am not getting.

Some additional details of my geometry:
Cylindrical bed : height-0.76m, radius-0.1m, flow inlet point radius-0.015m.
Inertial Resistance: 1.8e+05 1/m (in all directions)
Viscous Resistance: 1.53e+10 1/m2 (in all directions).
Meshing done is Cooper-type and grid size is 0.005.
Liquid used is Water and the bed used is Stationary.
Inlet velocity is of the order of 10^-3 - 10^-4 m/s.

I am using Fluent 6.3.26 and Gambit 2.4.

I am only observing a laminar plug flow through the center of the bed.

Any help, your opinion in this will be highly appreciated.

cdegroot August 7, 2012 03:03

When you say "dispersion" are you referring to thermal/species dispersion? If so this is quite another phenomenon that cannot simply be inferred by looking at the flow field.

If you specify a plug flow upstream, this profile will just carry itself through the porous medium. By continuity there is no reason for this to change. The only change will be that the pressure gradient will be higher due to the Darcy and Forchheimmer terms. Now, if you specify a pipe flow upstream you will get some radial flow as the fluid enters the porous medium and when it exits as the boundary layers must thin and form a plug flow. Can you clarify your inlet condition?


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