CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

inflow into closed container

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   June 10, 2011, 03:36
Default inflow into closed container
  #1
Member
 
EH
Join Date: Dec 2010
Posts: 61
Rep Power: 6
ehooi is on a distinguished road
Hi,
Is it possible to model, say a cylindrical domain where one one end, there is an inlet with a diameter smaller than the cylinder. At this end, the velocity inlet boundary condition is prescribed. The rest of the wall is assumed to be stationary no slip wall.

In this case, since we have an inlet flow into a closed domain, can the conservation of mass equation still be satisfied? I tried solving this in FLUENT and the solution converges. I am wary of its solution because intuition tells me that conservation of mass is not satisfied since there is no outflow to balance the inflow. Is the solution of FLUENT correct?

Thanks.

Sincerely,
EH
ehooi is offline   Reply With Quote

Old   June 10, 2011, 05:40
Default
  #2
Member
 
Ford Prefect's Avatar
 
Join Date: Mar 2009
Posts: 72
Rep Power: 8
Ford Prefect is on a distinguished road
Incompressible?
__________________
"Trying is the first step to failure." - Homer Simpson
Ford Prefect is offline   Reply With Quote

Old   June 10, 2011, 06:57
Default
  #3
Member
 
EH
Join Date: Dec 2010
Posts: 61
Rep Power: 6
ehooi is on a distinguished road
Yes, it is solved with the k-e model.
ehooi is offline   Reply With Quote

Old   June 10, 2011, 07:57
Default
  #4
Member
 
Ford Prefect's Avatar
 
Join Date: Mar 2009
Posts: 72
Rep Power: 8
Ford Prefect is on a distinguished road
Quote:
Originally Posted by ehooi View Post
Yes, it is solved with the k-e model.
I assume that you mean "Yes and it is solved with the k-e model.", hoping this is not a troll attempt.

Anyways, to your main question: No it should not work in this case, and I assume that your solution has not reached convergence and that you have terminated it before it blew up.

Cheers!
__________________
"Trying is the first step to failure." - Homer Simpson
Ford Prefect is offline   Reply With Quote

Old   June 10, 2011, 08:01
Default
  #5
Member
 
EH
Join Date: Dec 2010
Posts: 61
Rep Power: 6
ehooi is on a distinguished road
Quote:
Originally Posted by Ford Prefect View Post
I assume that you mean "Yes and it is solved with the k-e model.", hoping this is not a troll attempt.

Anyways, to your main question: No it should not work in this case, and I assume that your solution has not reached convergence and that you have terminated it before it blew up.

Cheers!
Well, I am solving a transient problem and my continuity criteria was set at 1e-6. After about 60s, the residual for continuity, velocities, k an e are less than 1e-6. When I plotted the contour for residual for mass imbalance, it is of the order of 10-9.
ehooi is offline   Reply With Quote

Old   June 10, 2011, 08:49
Default
  #6
Member
 
Ford Prefect's Avatar
 
Join Date: Mar 2009
Posts: 72
Rep Power: 8
Ford Prefect is on a distinguished road
If you calculate the mass flux across all boundaries what do you get?
__________________
"Trying is the first step to failure." - Homer Simpson
Ford Prefect is offline   Reply With Quote

Old   June 10, 2011, 09:11
Default
  #7
Member
 
EH
Join Date: Dec 2010
Posts: 61
Rep Power: 6
ehooi is on a distinguished road
I assumed you meant mass flow rate? Well, the mass flow rate at all the walls are zero except for the inlet where a value of 0.015kg/s was computed.

I guess it means there is a 0.015kg/s flow into the domain...but how is it that convergent is satisfied? This is puzzling. By the way, the mass flow rate at the interior calculated from fluent is -0.18kg/s...does this imply that mass vanishes somehow at the interior?
ehooi is offline   Reply With Quote

Old   June 10, 2011, 11:18
Default
  #8
Member
 
Ford Prefect's Avatar
 
Join Date: Mar 2009
Posts: 72
Rep Power: 8
Ford Prefect is on a distinguished road
Ok, I did a quick test with Fluent and I get the same results as you. However when I try the same in COMSOL and PHOENICS the solution diverges as expected. I have no good explanation as to why this works in Fluent. I will think more on the matter during the weekend. A cold beer is a good catalyst for "problems" like this

Cheers!
__________________
"Trying is the first step to failure." - Homer Simpson
Ford Prefect is offline   Reply With Quote

Old   June 13, 2011, 01:25
Default
  #9
Member
 
EH
Join Date: Dec 2010
Posts: 61
Rep Power: 6
ehooi is on a distinguished road
Quote:
Originally Posted by Ford Prefect View Post
Ok, I did a quick test with Fluent and I get the same results as you. However when I try the same in COMSOL and PHOENICS the solution diverges as expected. I have no good explanation as to why this works in Fluent. I will think more on the matter during the weekend. A cold beer is a good catalyst for "problems" like this

Cheers!
Hi,
If you happen to check the mass flow rate on the boundary, there is a positive flow rate into the container. However, if you calculate the mass flow rate at the interior as well, then there is a sink, which is somehow greater than the net mass flow rate at the boundary (at least in my model). Really puzzling...
ehooi is offline   Reply With Quote

Old   June 13, 2011, 05:03
Default
  #10
Member
 
Ford Prefect's Avatar
 
Join Date: Mar 2009
Posts: 72
Rep Power: 8
Ford Prefect is on a distinguished road
Quote:
Originally Posted by ehooi View Post
Hi,
If you happen to check the mass flow rate on the boundary, there is a positive flow rate into the container. However, if you calculate the mass flow rate at the interior as well, then there is a sink, which is somehow greater than the net mass flow rate at the boundary (at least in my model). Really puzzling...
Yes it is, however as I see it the net flow rate is unaffected by the value in the interior. Strange.
__________________
"Trying is the first step to failure." - Homer Simpson
Ford Prefect is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
reefer container arabITS Main CFD Forum 1 November 2, 2010 03:13
Turbulent Inflow Conditions ali OpenFOAM Running, Solving & CFD 2 July 9, 2009 09:55
Prescribed inflow velocity profile - how to? Alan Main CFD Forum 10 October 28, 2005 12:14
pressure distribution in a closed container prasanth FLUENT 3 December 21, 2003 08:21
Inflow condition for the liquid fuel pool fire Jianping Zhang Main CFD Forum 0 May 1, 2003 07:24


All times are GMT -4. The time now is 00:04.