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Velocity in porous domain in CFX post

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Old   July 2, 2012, 09:23
Default Velocity in porous domain in CFX post
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Hi,

CFX Post gives the following variables as output: Velocity, Velocity u, Velocity v and Velocity w.
What do these velocity components mean when they pertain to porous medium? Do they mean true velocities or superficial velocities?
It seems like these may be true velocities but I am not sure.

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Old   July 5, 2012, 19:21
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they represent true velocities if you set the porous membrane to "true velocity"
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Old   May 19, 2015, 11:02
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Hi all,

I am trying to simulate a flow through a porous domain. From a detailed model I got that my pressure from was 10Pa over 0.3m at 2m/s which gives me Kq of 16.67. My problem is that air at 2m/s comes to the porous domain but then suddenly changes velocity to around 5-6m/s. Should the air be slower in porous domain? Anyone has any idea why this is happening?

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Old   May 19, 2015, 11:41
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There is a lot of topic related to porous domain here:

Porous domain - Volume porosity change ... no effect??

CFX consider a porous domain with a "volume ratio coefficient" (your fluid can go in only x% of the domain) so to keep the same massFlow, your fluid has to accelerate.

have a look on the CFX User guide, the porous section is not the best at all but it could help you to understand what CFX do here.
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Old   May 19, 2015, 13:59
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Hey,

Yeah I figured it out 5 minutes after I posted. Actually, it is pretty stupid, I put that the volume ratio is 0.8 thinking that it would be the volume occupied, and not volume free for flow. When I put it to 0.2 it gives me what I expect. The tutorial on flow in porous domain confused me a little bit...
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Old   May 20, 2015, 04:12
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Yep, I agree that the section about this subject on ANSYS Help is not the best (i didn't try the tutorial).
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