# Velocity in porous domain in CFX post

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 July 2, 2012, 09:23 Velocity in porous domain in CFX post #1 Senior Member   Join Date: Oct 2010 Location: Zurich Posts: 176 Rep Power: 6 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. Thanks!

 July 5, 2012, 19:21 #2 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 486 Rep Power: 9 they represent true velocities if you set the porous membrane to "true velocity"

 May 19, 2015, 11:02 #3 New Member   Join Date: Mar 2015 Posts: 14 Rep Power: 2 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? Thanks

 May 19, 2015, 11:41 #4 Senior Member   Thomas MADELEINE Join Date: Oct 2014 Posts: 122 Rep Power: 2 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.

 May 19, 2015, 13:59 #5 New Member   Join Date: Mar 2015 Posts: 14 Rep Power: 2 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...

 May 20, 2015, 04:12 #6 Senior Member   Thomas MADELEINE Join Date: Oct 2014 Posts: 122 Rep Power: 2 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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