Hallo everybody!

I've only just begun to work with Fluent (V6.2). I want to use the VOF model to simulate an open channel flow. My geometry consists of the river bed (trapezoidal cross-section, water level approx. 5m) and a layer of air above it. I'm not clear about how to set the boundary conditions (BC).

Which area has to be taken for the inlet? Just the area where the water enters or also the area of air?

I'm grateful for any advise!

Christine

hi chirs..... me too new to fluent but i guess u will have to specify the in let as both air and water crossections.....try it ....it might just work....best of luck

Dear Christine:

You can use all of boundary condition types in VOF open channel model. However, Mass flow inlet and pressure outlet/inlet are preffered and more used. But, you have to choose the boundary condition based on the problem specifications. If you know the flowrate, use mass flow inlet. I this boundary condition type, you can set the initial water level(would be changed during solve) and specified constant water and air mass flowrate. But if you know the water level and change of flowrate is not important choose pressure inlet/outlet BC. In this BC you do not need to enter air flowrate, and just enter free surface water level. However, if the wind effects in negligible in your problem, it is not nesseecary to enter air flowrate. Also, you can choose combinations of other BC for modeling your problem. Remember to DO NOT choose preesure inlet for upper boundary(atmosphere). Althogh is seems logical but causes divergence.

I recommend to use smaller model, considering scale effects in river flow modelling, if possible. If you want to study on secondary flows or compound channel, use scaled model, because you have to define very large mesh on this geometry and your CPU consumed time will be too long. but, if meandering effects is important do not use scaled model.

Wish to be useful.

Best Regards

Mehdi Ghoddosy

Dear Christine:

Reading these two papers can give you a valuable help and vision:

Matthews, C. A., et al..;"Computaions of Curved Free Surface Water Flow On Spiral Concentrators"; ASCE journal of hydraulic engineering, Vol.125,pp??,Nov. 1999,

and related discussion as:

Fabian, A., et al.; ASCE journal of hydraulic engineering, pp629-631,July 2001

Best Regards

Mehdi Ghoddosy

Dear Mehdi,

thank you. That was very useful. I happened to find both publications in our library.

Best regards Christine

[mechovator]

Hello dear christine.

I just saw your problem and learned that you got its solution. I have just started my MS and am working in the same field. It would be very nice of you if you could please help me. Feel free to contact me on

mechovator@yahoo.com

With best regards

Mechovator

[s_saleh]

Hi Dear Ghoddosy
I am working with fluent (v. 12) and I want to model an 2d open channel with a wheel in open channel that raotates and moves the water in channel.
I have problems with boundary conditions.for setting BC in water and air.
should I set separate BC for water and air region?how?
regards
Saleh