boundary conditions in FLUENT VOF for open channel flow

newcomer · March 24, 2011, 05:04

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, 01:58

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, 09:08

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, 19:13

Quote:

Originally Posted by newcomer

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, 19:18

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

flow_CH · June 2, 2013, 09:32

Quote:

Originally Posted by newcomer

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.

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, 04:07

Quote:

Originally Posted by mkhodier

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, 15:23

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, 12:19

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

OJ

mkhodier · June 10, 2013, 14:18

mkhdcpu1@yahoo.com Thank you for your help

flow_CH · June 10, 2013, 14:53

saeed.azsh88@gmail.com thank you

Bhargav93 · July 7, 2013, 05:33

ybhargav93@gmail.com thank u

blek · July 17, 2013, 03:51

tomo.umor@gmail.com thanks for help

OttawaCFD · July 22, 2013, 17:37

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

Kesselteufel · July 29, 2013, 05:38

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

matthias.hoefler@rwth-aachen.de

OttawaCFD · July 29, 2013, 12:58

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

es99 · August 10, 2013, 04:46

Hi,
Thank you
mostafashamsi.es99@yahoo.com

JAY ADHVARYU · August 25, 2013, 10:05

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.

March 24, 2011, 05:04	boundary conditions in FLUENT VOF for open channel flow	#1
newcomer New Member Gillian Join Date: Sep 2010 Posts: 15 Rep Power: 16	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 justsmile2007 likes this.

April 5, 2011, 01:58		#4
newcomer New Member Gillian Join Date: Sep 2010 Posts: 15 Rep Power: 16	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 gangadhar likes this.

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March 24, 2011, 05:36		#2
momech New Member mohsen Join Date: Feb 2011 Posts: 13 Rep Power: 15	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.

March 26, 2011, 09:03		#3
newcomer New Member Gillian Join Date: Sep 2010 Posts: 15 Rep Power: 16	hi momech, Thanks a lot for the suggestion!

April 5, 2011, 09:08		#5
momech New Member mohsen Join Date: Feb 2011 Posts: 13 Rep Power: 15	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.

April 16, 2013, 19:18		#7
mkhodier New Member Moahanad Join Date: Apr 2013 Posts: 6 Rep Power: 13	did u figure out the problem, if u did, could u help me. Thank you.

June 6, 2013, 15:23		#10
mkhodier New Member Moahanad Join Date: Apr 2013 Posts: 6 Rep Power: 13	Thank you for replying. Could you please send me the tutorial, I can't find it. Thank you for your help.

June 10, 2013, 12:19		#11
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	Can you post you email address? I can sent it across to you. OJ

June 10, 2013, 14:18		#12
mkhodier New Member Moahanad Join Date: Apr 2013 Posts: 6 Rep Power: 13	mkhdcpu1@yahoo.com Thank you for your help

June 10, 2013, 14:53		#13
flow_CH Senior Member FHydro Join Date: Jan 2013 Posts: 197 Rep Power: 13	saeed.azsh88@gmail.com thank you

July 7, 2013, 05:33		#14
Bhargav93 New Member Bhargav Join Date: Jun 2013 Posts: 6 Rep Power: 13	ybhargav93@gmail.com thank u

July 17, 2013, 03:51		#15
blek New Member tomo umor Join Date: Jul 2013 Posts: 7 Rep Power: 13	tomo.umor@gmail.com thanks for help

July 22, 2013, 17:37		#16
OttawaCFD New Member Derek Foran Join Date: Jul 2013 Posts: 10 Rep Power: 13	servicesamigo@gmail.com If it's still out there, thanks!

July 29, 2013, 05:38		#17
Kesselteufel New Member Join Date: Jul 2013 Posts: 1 Rep Power: 0	I am also searching for the tutorial, if someone would send it to: matthias.hoefler@rwth-aachen.de

July 29, 2013, 12:58		#18
OttawaCFD New Member Derek Foran Join Date: Jul 2013 Posts: 10 Rep Power: 13	I have not received it yet either, I guess it no longer is out there

August 10, 2013, 04:46		#19
es99 New Member mostafa shamsi Join Date: Aug 2013 Location: iran Posts: 4 Rep Power: 13	Hi, Thank you mostafashamsi.es99@yahoo.com

August 25, 2013, 10:05		#20
JAY ADHVARYU New Member JAY Join Date: Jul 2013 Posts: 10 Rep Power: 13	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.