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-   -   boundary conditions in FLUENT VOF for open channel flow (https://www.cfd-online.com/Forums/fluent-multiphase/86501-boundary-conditions-fluent-vof-open-channel-flow.html)

 newcomer March 24, 2011 05:04

boundary conditions in FLUENT VOF for open channel flow

Hi guys,

I have been working on the simulation of flow in a channel through a baffle using VOF FLUENT. I encountered a few problems and would appreciate it if you could please give me some suggestions:

Currently I am using two separate inlets for water and air. The BC for air is set as pressure inlet. I have tried 3 types of BC for water (pressure-inlet, mass flow, and velocity - as the velocity is known) but the simulation somehow gave me a flow direction that looks like the water flows from outlet back to the inlet. The outlet is set as 1 outlet (for both water and air) and operated as pressure outlet. The top surface of air is also set as pressure outlet.

I am wondering if there is some problems with my current setting ?

Your suggestions are very much appreciated.

Gillian

 momech March 24, 2011 05:36

hi.
you should not separate the inlet or outlet for water and air.it's better to use OPEN CHANNEL FLOW by switch it's toggle on and set the inlet and outlet as PRESSURE INLET/OUTLET one and entered your data.also it's better too use ''explicit'' method {define>models>multiphase.....}
good lock.

 newcomer March 26, 2011 09:03

hi momech,

Thanks a lot for the suggestion!

 newcomer April 5, 2011 00:58

Hi,

I tried the simulation with one inlet for the two phase but could not get the results right. The solution still did not converge and another serious issue is the results gave me reverse flow at the inlet.

My boundary conditions are:
1. inlet: pressure inlet, with specifying the flow depth at the inlet
2. outlet: pressure outlet, with flow depth specified (which is lower than in the inlet, due to pressure drop across the baffle)
3. upperbound : I have tried either pressure outlet and symmetry.

Would appreciate it very much if anyone please give me some suggestions on how to solve the problem of reverse flow at the inlet during the simulation.

Indeed, I tried to use velocity inlet as BC for inlet. However, I am a bit confused of how to come up with the volume fraction of water and air respectively (in my physical model, the flow is at 0.04 m/s). Besides, it seemed that with velocity inlet, I could not initialize using open channel initialization. Can anyone give me some suggestions on how should i set velocity inlet BC for open channel ?

Thanks a lot!

Gillian

 momech April 5, 2011 08:08

Hi newcomer
I did the 3D open channel case with cutwater and get acceptable results, it seems that you didn't patch your desired area/volume with water and its velocity after initialize.

best regards.

 mkhodier April 16, 2013 18:13

Quote:
 Originally Posted by newcomer (Post 300842) Hi guys, I have been working on the simulation of flow in a channel through a baffle using VOF FLUENT. I encountered a few problems and would appreciate it if you could please give me some suggestions: Currently I am using two separate inlets for water and air. The BC for air is set as pressure inlet. I have tried 3 types of BC for water (pressure-inlet, mass flow, and velocity - as the velocity is known) but the simulation somehow gave me a flow direction that looks like the water flows from outlet back to the inlet. The outlet is set as 1 outlet (for both water and air) and operated as pressure outlet. The top surface of air is also set as pressure outlet. I am wondering if there is some problems with my current setting ? Your suggestions are very much appreciated. Gillian
Hi guys;
anyone can help me with setting the boundary conditions in the open channel flow? Thanks

 mkhodier April 16, 2013 18:18

did u figure out the problem, if u did, could u help me. Thank you.

 flow_CH June 2, 2013 08:32

Quote:
 Originally Posted by newcomer (Post 302229) Hi, I tried the simulation with one inlet for the two phase but could not get the results right. The solution still did not converge and another serious issue is the results gave me reverse flow at the inlet. My boundary conditions are: 1. inlet: pressure inlet, with specifying the flow depth at the inlet 2. outlet: pressure outlet, with flow depth specified (which is lower than in the inlet, due to pressure drop across the baffle) 3. upperbound : I have tried either pressure outlet and symmetry. Would appreciate it very much if anyone please give me some suggestions on how to solve the problem of reverse flow at the inlet during the simulation. Indeed, I tried to use velocity inlet as BC for inlet. However, I am a bit confused of how to come up with the volume fraction of water and air respectively (in my physical model, the flow is at 0.04 m/s). Besides, it seemed that with velocity inlet, I could not initialize using open channel initialization. Can anyone give me some suggestions on how should i set velocity inlet BC for open channel ? Thanks a lot! Gillian
I have exactly this problem . :(
I am using "Open channel flow" option in inlet and outlet boundaries. It is look like water goes up in pressure inlet boundary.:confused::confused:
Where is the origin of the free surface and bottom. Is it in bottom of any boundary or origin of coordinates?
help me please.

 Sam Engineer June 3, 2013 03:07

Quote:
 Originally Posted by mkhodier (Post 421058) Hi guys; anyone can help me with setting the boundary conditions in the open channel flow? Thanks
Hi
please read "Heave and Pitch Simulation of Ship hull moving through head sea waves" tutorial

 mkhodier June 6, 2013 14:23

Thank you for replying. Could you please send me the tutorial, I can't find it. Thank you for your help.

 oj.bulmer June 10, 2013 11:19

Can you post you email address? I can sent it across to you.

OJ

 mkhodier June 10, 2013 13:18

mkhdcpu1@yahoo.com Thank you for your help

 flow_CH June 10, 2013 13:53

saeed.azsh88@gmail.com thank you

 Bhargav93 July 7, 2013 04:33

ybhargav93@gmail.com thank u

 blek July 17, 2013 02:51

tomo.umor@gmail.com thanks for help

 OttawaCFD July 22, 2013 16:37

servicesamigo@gmail.com If it's still out there, thanks!

 Kesselteufel July 29, 2013 04:38

I am also searching for the tutorial, if someone would send it to:

matthias.hoefler@rwth-aachen.de

 OttawaCFD July 29, 2013 11:58

I have not received it yet either, I guess it no longer is out there

 es99 August 10, 2013 03:46

Hi,
Thank you
mostafashamsi.es99@yahoo.com

 JAY ADHVARYU August 25, 2013 09:05

I have some problem with my boundary condition that how i utilize the neumann condition(∂φ/∂x = 0) at outlet. Can i select pressure outlet at outlet?
my inlet condition is :
flat velocity profile =40m/s
Re=1.916*10^5
turbulent intensity=4.5%
And Inlet height of duct=5mm

I select velocity inlet at inlet because my flow is incompresible.
And axis boundary condition applied along the centerline.
and no slip condition at wall.

pls help me.

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