Hi all,

I have a cylinder, open to atmosphere, consisting of two layers of different porous media each.Water flows in the cylinder at a very low rate. The viscous resistances in the two layers are such that one is 10^4 times the other.In the velocity contours,I expect to see higher velocity in the layer with less viscous resistance.But in the contours I see that velocity in the cylinder is same throughout.

I give velocity-inlet B.C. for the top face, pressure-oulet B.C. for the bottom face and wall B.C. for the side of the cylinder.I enable porous zone option for each of the two layers

why is this happening? Any idea?

Anitha.

Use physical velocity formulation in solver settings. I think you have used Superficial velocity.

-Prakash

Hi Prakash, I tried it, but of no use Its still giving same velocity throughout By the way do resistance coefficients affect the velocity?If so,how?

TIA Anitha

hi Anitha, yes resistance coefficients affect the velocity. You have to supply viscous and inertial resistance coefficients. note that viscous resistance coefficents is 1/alpha (You have to specify it) ==> lower the coefficient means higher the resistance which results in higher velocity. For more help read the manual to calculate these coefficients which depend on particle size.

hope it helps -Prakash

Hi Anitha!

If you cylinder has only one diameter, then it's correct that the velocity is the same (at least if it has side walls) because of the continuity... same mass flow and flow surface - same velocity...

But the pressure drop will be higher in the area with the higher resistance...

check that..

sorry for my poor english!

korni

Hi,

Go for pressure inlet and pressure outlet BC if u kno pressure drop. then u can c variable velocity. regards.. Thiyaga.

hi Thiyaga,

As I have said earlier, my cylinder is placed in open space so that pressure at the inlet and pressure at the outlet is also the same i.e. 1 atm.Infact I have tried this out but there is no flow at all.

So I started giving velocity-inlet at the inlet (since I know the incoming flow-rate) and pressure outlet at the bottom

What do you say?

Regards, Anitha.

hi Thiyaga,

As I have said earlier, my cylinder is placed in open space so that pressure at the inlet and pressure at the outlet is also the same i.e. 1 atm.Infact I have tried this out but there is no flow at all.

So I started giving velocity-inlet at the inlet (since I know the incoming flow-rate) and pressure outlet at the bottom

What do you say?

Regards, Anitha.

Hi,

there should be some pressure gradient, then only flow will occur through the porous media, calculate the value of pressure drop with Darcy's eqn (6.19.5 of Fluent6.1 manual), i think u know the value of permeability and velocity.use P(inlet)=P(outlet)+del P. hope this would help. regards Thiyaga.