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Andy Chen July 9, 2009 03:04

open channel problem (free surface)
Dear experts :

I simulated open channel. I have some question. Please experts help me. And my following:

fluent 3dp

read case .

grid check.

define models solver time(steady)ok.

define models multiphase volume of fluid open channel flow ok implicit body force ok.

define models energy not selected ok.

define models viscous k epsilon model RNG standard wall function ok .

define materials water liquid copy create.

Define phases phase 1 air, phase 2 water liquid close.

Define operation conditions gravity X coordinate 0.017 Z coordinate -9.81 specified operation density selected ok.

Define boundary conditions inflow mass-flow-inlet phase mixture open channel Free surface level 0.25 (m) bottom level 0.0 (m) k and epsilon ok.

Define boundary conditions outflow outflow phase mixture flow rate weighting 1.0 ok.

Define boundary conditions wall (left, bottom, right boundary ) wall momentum roughness height 0.02 roughness constant 0.5 ok.

Define boundary conditions top boundary symmetry ok.

Solve controls solutions piso algorithm pressure body force weighted ok.

Solve initialize compute from inflow lint close.

Solve initialize patch volume fraction value 1 patch.

Solve monitors residual plot select ok.

Solve iterate .

My inflow free surface level is 0.25 m, and my dike is 0.4 m. When I iterate over that my water depth is 0.4 m, isn't 0.25 m. It's so strange. I use VOF model, but my result didn't have free surface. Please experts help me. It's big problem for me.

Thanks your help.

John July 9, 2009 09:16

"Define boundary conditions top boundary symmetry ok."

Is this right for free surface problem?

Andy Chen July 9, 2009 09:58


Originally Posted by John (Post 222088)
"Define boundary conditions top boundary symmetry ok."

Is this right for free surface problem?

Yes, I simulated open channel (free surface ) problem. Did I set wrong on top boundary? Then, how did I set on top boundary ?

Very thanks your help, John.

Andy Chen July 9, 2009 23:38

Please, could anyone help me?

I really want to experts solve my problem.

It's really a big problem for me. So, please help me!

vovman July 10, 2009 01:20

It's hard to simulate open channel in Flunet.

Extend your two side boundaries to the height which free surface may be.
And combined the top boudnary to form a upside down U shape boundary.
Then set it to : pressure inlet

When you use symmetry, it assume no flux across. If the free surface is higher than that, it can't cross the top lid.

This may solve it and btw use 2d first to test it.

If you suceed, tell us how you have done it.

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