open channel problem (free surface)

Andy Chen · July 9, 2009, 04:04

Dear experts :

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

fluent 3dp

file ® 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, 10:16

"Define ® boundary conditions ® top boundary ® symmetry ® ok."

Is this right for free surface problem?

Andy Chen · July 9, 2009, 10:58

Quote:

Originally Posted by John

"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 10, 2009, 00:38

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, 02:20

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.

July 9, 2009, 04:04	open channel problem (free surface)	#1
Andy Chen Member Yi-Lang Chen Join Date: May 2009 Posts: 58 Rep Power: 17	Dear experts : I simulated open channel. I have some question. Please experts help me. And my following: fluent 3dp file ® 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.

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July 9, 2009, 10:16		#2
John Member Join Date: Mar 2009 Posts: 49 Rep Power: 17	"Define ® boundary conditions ® top boundary ® symmetry ® ok." Is this right for free surface problem?

July 10, 2009, 00:38		#4
Andy Chen Member Yi-Lang Chen Join Date: May 2009 Posts: 58 Rep Power: 17	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!

July 10, 2009, 02:20		#5
vovman New Member Join Date: May 2009 Posts: 1 Rep Power: 0	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.