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-   -   Velocity in Porous medium : HELP! HELP! HELP! (https://www.cfd-online.com/Forums/phoenics/52116-velocity-porous-medium-help-help-help.html)

 Kali Sanjay November 6, 2006 06:10

Velocity in Porous medium : HELP! HELP! HELP!

Dear Friends!

I have a query regarding solving of velocity in a porous domain. I have a sort of tube which is filled with soil in a section which causes the area to decrease. The tube is left to open at both ends. I am solving for a velocity profile and the source of velocity is due to electroosmosis in the soil which is a function of x(sort of pumps in series of different capacities ).

--Non-porous--|---Soil-Porous---|--Non-porous--

So soil acts like a pump. I am solving for 1-D Cartesian coordinates and I can write the velocity as

d((Ke*dV/dx)+(Kh*dp/dx)/dx=0

Actually the part Ke*dV/dx is source of velocity which I can calculate. The second part of the above equation will be calculated for satisfying continuity equation. As the velocity is different , the pressure actually will compensate for making it uniform. I hope I can solve this problem using PHOENICS.

I gave the porosity as

CONPOR(CAREA,PRST,CELL,#2,#2,1,1,1,1)

Where my region 2 is packed with soil.

I calculated Ke*dv/dx at every point in the soil and specified as velocity source in ground.

PATCH(VSPD,CELL,1,NX,1,1,1,1,1,LSTEP) COVAL(VSPD,U1,FIXVAL,GRND)

In GROUP 13 for GRND (Value), I specified Ke* dv/dx........v is potential (volts)

I specified pressure boundary conditions as P=0 at ends with initial Pressure P specified as Zero at all points.

These are my inital and boundary conditions for U1 and P1

FIINIT(U1)=1E-10 FIINIT(P1)=0

PATCH(ANODE,WEST,1,1,1,1,1,1,1,LSTEP) COVAL(ANODE,P1,FIXP,0.0) COVAL(ANODE,U1,ONLYMS,0.0)

PATCH(CATHODE,EAST,NX,NX,1,1,1,1,1,LSTEP) COVAL(CATHODE,P1,FIXP,0.0) COVAL(CATHODE,U1,ONLYMS,0.0)

Is it the correct way? I have found that when CONPOR is specified as CELL, the AEAST shows the same area as non-porous region and I think the volume decreases, but area remains same (Internally propably PHOENICS takes volume as DXU2D *AEAST*Porosity). In that case the velocity that I need to specify should be superficial velocity. What I know Ke * dv/dx is actual velocity in pore. Do I need to multiply this velocity with porosity and give as area patch for velocity?

I am not sure whether I had pose my problem correctly or not, in summary, 1. Is CONPOR fixing the way I did is OK? 2. Can I specify known velocity field in the cells and set PHOENICS to solve for pressure to satisfy the continuity equation and get uniform velocity? I just know pressure at ends (atmosphere) and velocity source Ke*dv/dx in soil. 3. Do I need to activate DARCY=T and fix DARCON for #2 region?