Doubt regarding modeling a downstream porous media in Ansys Fluent

[khojax77]

Hi,

 

I’m running a CFD case in ANSYS Fluent 2024R2 and have a conceptual question about porous media placement. The model has flow passing through module 1 (which is a large porous media) and I introduced another porous media thin body intended to act as a flow-redistributor. When the porous media is placed upstream of module 1, the velocity distribution entering the module becomes noticeably more uniform, which is what I expect.

 

However, when I place the same porous media (same coefficients and setup) downstream of module 1, the velocity distribution upstream of the module appears unchanged. My question is both about the physics and the software implementation:

 

• Should one expect a downstream porous resistance to influence the upstream velocity distribution in a noticeable way? or is it normal that the upstream distribution remains unchanged in this case?
• Physics wise, In other words, in a subsonic internal flow system, to what extent can a downstream porous resistance redistribute flow upstream of another component?

 

I’m trying to understand whether this behaviour is physically expected or if there is something in my setup that I should perhaps revisit.

 

Thanks!

[Rob]

Porous media is a lumped pressure loss: so designed to produce an excess pressure loss to mimic filters, pipes, leaves etc. It won't accelerate flow. 

In your system you have two extra pressure losses due to the porous media. Plus whatever pressure loss comes from the domain itself (people always forget about that bit). 

 

Now thinking about your flow question, and also treading carefully to keep this "public" knowledged. If I have a pipe with a pin-hole orifice plate that is my main pressure drop, I'd expect that to dominate the flow. Adding a sponge layer up or downstream of that with a very low resistance to flow won't have any effect upstream, and minimal effect downstream (it'll slow the jets up a bit).