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What does it mean....????

Dear FLUENT USERS,

Wish you all a VERY HAPPY & PROSPOROUS NEW YEAR!!!

I am trying to model the upward seepage(also known as influent seepage or Injection) through the porous bed of an open channel.

For this I created necessary geometry in GAMBIT and called the bed of channel as "bott-face" and set it as "Porous Jump" boundry condition, and exported the mesh to FLUENT-5.

But while reading the .msh file in FLUENT-5, the following error message appears ....

"Can not change "bott-face" to "Porous Jump" because there is only one adjacent cell thread"

What does this mean? How to set the "Porous Jump" B.C. in Gambit?

 Jin-Wook LEE January 2, 2002 02:55

Re: What does it mean....????

I guess that your 'porous jump' is located at the boundary. Porous jump shoud not be located at the boundary.

Sincerely, Jinwook.

Re: What does it mean....????

Dear Jeanwook,

Consider that flow depth in channel is 25 cm & the underlying sand bed has a thickness of 10cm. Where should the porous jump be located? Pl. reply.

Sincerely,

 Jin-Wook LEE January 2, 2002 05:41

Re: What does it mean....????

'underlying sand bed has a thickness of 10cm'. --> Then set the region of sand bed as porous media. For 3D analysis, porous media is for the volume and porous jump is for the surface.

Sincerely, Jinwook

Re: What does it mean....????

Dear Jeenwook,

If go for 3D flow, what boundary condition should I set at the interface of water and sand bed?

I know the seepage velocity at the interface of water and sand bed which is very low(0.0004m/s). With this velocity water enters the main channel flow which is turbulent. The problem is how to simulate the roughness of sand bed and upward velocity with a Single Boundary condition.

If I set "velocity inlet" B.C. for this bed, roughness effect is not taken into account & if I set it as "wall" BC, then I can not set the velocity. Also from which zone FLUENT should be made to solve for the solution in the "Initialize" panel?

 Jin-Wook LEE January 2, 2002 20:24

Re: What does it mean....????

CFD can do something not everything. But fortunately, if you set the sand region as 'POROUS ZONE', the overall effect can roughly be included in the 'porous region'.

Sincerely, Jinwook

 Carlos January 5, 2002 13:41

Re: What does it mean....????

I hope your simulation is not transient or reacting.

If it is, it will be WRONG. Fluent does not take into account the porosity in the transport equations.

Re: What does it mean....????

Hi Carlos,

Please explain in detail what you wanted to state. Thanks!

Re: What does it mean....????

Dear Jeenwook,

Could you please reply each questions one by one basis. I am not getting response from other users hence troubling you.

Q1.If I go for 3D flow, what boundary condition should I set at the interface of water and sand bed?

I know the seepage velocity at the interface of water and sand bed which is very low(0.0004m/s). With this velocity water enters the main channel flow which is turbulent. The problem is how to simulate the roughness of sand bed and upward velocity with a Single Boundary condition.

If I set "velocity inlet" B.C. for this bed, roughness effect is not taken into account & if I set it as "wall" BC, then I can not set the velocity.

Q2.From which zone FLUENT should be made to solve for the solution in the "Initialize" panel?