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-   -   Open Channel Flow (http://www.cfd-online.com/Forums/fluent/86059-open-channel-flow.html)

 ElanMorin March 13, 2011 18:36

Open Channel Flow

Hi,

I'm currently trying to perform a simple open channel flow simulation using Fluent 6.3.26 and having absolutely no luck. I've tried looking for tutorials online but haven't found any worth mentioning as they don't cover what I'm trying to do.

The current problem I'm trying to solve is a simple geometry as follows:

http://i.imgur.com/HQ5NZ.jpg (Link to well known image hosting website)

The picture shows what I expect the results to be and the boundary conditions that I've set.

The length of the model is 2 meters and the height is 0.5 meters. The aim I'm trying to achieve with this simulation is just to get a working open channel flow example.

Starting from opening Fluent, these are the steps I would expect to take:

-------------------------------------

Define -> Operation Conditions
Tick: gravity -> Y = -9.81
Define -> Models -> Multiphase
Volume of Fluid -> Tick: Open Channel Flow (Implicit)
Define -> Materials
Define Water
Define -> Phases
phase-1: primary-phase -> air
phase-2: primary-phase -> water
Define -> Boundary Conditions:
Inlet: mass-flow-inlet
Mixture: Multiphase -> Tick: Open Channel
Free Surface Level = 0.2
Bottom Level = 0.1
air: Momentum -> Mass Flow-Rate = 1kg/s
water: Momentum -> Mass Flow-Rate = 100kg/s
Outlet: pressure-outlet
Mixture: Multiphase -> Tick: Open Channel
Free Surface Level = 0.1
Bottom Level = 0
Solve -> Initialize -> Init

Solve -> Iterate (1000 iterations)

-------------------------------------

I've also tried, unsteady flow, different flow rates including zero for both air and water, ticking or unticking open channel flow at the outlet, and adding various turbulence models. Though if you think these to be the problem, please say, as I may have been adding half the right things but missing out crucial components.

I have also tried different mesh densities (9,000 elements to 255,000 elements)

The current results I attain show a contour phase plot of all air.

My question is simply, what have I done wrong? I have been trying to follow the open channel flow user guide notes from Fluent, and (I think) done everything they say, but still get spurious results.

 Sushilkumar March 14, 2011 01:56

I presume you are simulating it in 2D.

what fluid heights you have mentioned at the inlet and outlet locations..?

 ElanMorin March 14, 2011 05:45

Thanks very much for the reply!

My apologies, yes it's 2D.

I've set the fluid heights at 0.1m at the inlet and outlet. Does this significantly change the motion of the fluid downstream? At the inlet it would make a difference but I fail to see what setting a height of 0.1m at the outlet achieves.

 seyedashraf August 19, 2011 15:21

air: Momentum -> Mass Flow-Rate = 0.0001kg/s

also you have patched the water section , or not mentioned here
you had to define water in adapt=> region => mark and close
after the initialization, patch the marked section

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