CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Why mass flow is 0?

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 30, 2016, 06:34
Default Why mass flow is 0?
  #1
New Member
 
Liang shuai
Join Date: Nov 2015
Posts: 13
Rep Power: 7
Sataha is on a distinguished road
I built several domains to calculate the an steam impingement from a orifice to a porous media.

But as soon as I finished the calculation. I fond a problem is that the mass flow from inlet is not equal to the out. As it is shown in the picture and it is marked as red. The outlet is 0 and I have checked the settings of CFX and I can not find any error.

The other results is just as I expected, such as temperature and viscosity. But I cannot find where is wrong about the mass flow.

Thank you for your help!
Attached Images
File Type: jpg 20160530182613.jpg (195.3 KB, 20 views)
Sataha is offline   Reply With Quote

Old   May 30, 2016, 07:00
Default
  #2
Senior Member
 
Maxim
Join Date: Aug 2015
Location: Germany
Posts: 410
Rep Power: 9
-Maxim- is on a distinguished road
please share more information about your project. Attach screenshots and your out-file.
Do you have defined the interfaces between the domains properly?
-Maxim- is offline   Reply With Quote

Old   May 30, 2016, 09:19
Default
  #3
New Member
 
Liang shuai
Join Date: Nov 2015
Posts: 13
Rep Power: 7
Sataha is on a distinguished road
Quote:
Originally Posted by -Maxim- View Post
please share more information about your project. Attach screenshots and your out-file.
Do you have defined the interfaces between the domains properly?
Thank you for your reply.

I have defined the interfaces between the domains, but I am not sure about if it is properly.

I have some supplementary information in the attachment.

The first pic shows the interface I set up. The yellow circle is the interface domain, which is the end of the orifice (orifice outlet). The second pic is the set up of inlet conditions.
Attached Images
File Type: jpg B6B2DTN6X@4UM}94QUUB~A0.jpg (77.4 KB, 19 views)
File Type: png 40_KZ%~VTUSZAF}1_}8J0NA.png (18.4 KB, 12 views)
Sataha is offline   Reply With Quote

Old   May 30, 2016, 09:23
Default
  #4
Senior Member
 
Maxim
Join Date: Aug 2015
Location: Germany
Posts: 410
Rep Power: 9
-Maxim- is on a distinguished road
your ccl and/or out file would help us more The out-file is generated by the solver manager and has the same name as your res file.
-Maxim- is offline   Reply With Quote

Old   May 30, 2016, 09:48
Default
  #5
New Member
 
Liang shuai
Join Date: Nov 2015
Posts: 13
Rep Power: 7
Sataha is on a distinguished road
Quote:
Originally Posted by -Maxim- View Post
your ccl and/or out file would help us more The out-file is generated by the solver manager and has the same name as your res file.
the attachment is my out file and I deleted some loop interactions as it exceeded the size requirement of forum.

Thank you!
Attached Files
File Type: txt result.txt (144.1 KB, 8 views)
Sataha is offline   Reply With Quote

Old   May 31, 2016, 10:57
Default
  #6
Senior Member
 
Join Date: Jun 2009
Posts: 1,369
Rep Power: 25
Opaque will become famous soon enough
Your solution has not converged yet.. Far from it.

You can check the mass imbalance for the domain "fabric backside" and "fabric front", and the continuity equation has not been fully satisfied.

In addition, the message for stopping the run says:

Quote:
================================================== ====================
Termination and Interrupt Condition Summary
================================================== ====================

CFD Solver: Run duration reached
(Maximum number of outer iterations)
You ran out of iterations w/o achieving convergence.
Opaque is offline   Reply With Quote

Old   May 31, 2016, 12:07
Default
  #7
New Member
 
Liang shuai
Join Date: Nov 2015
Posts: 13
Rep Power: 7
Sataha is on a distinguished road
Quote:
Originally Posted by Opaque View Post
Your solution has not converged yet.. Far from it.

You can check the mass imbalance for the domain "fabric backside" and "fabric front", and the continuity equation has not been fully satisfied.

In addition, the message for stopping the run says:



You ran out of iterations w/o achieving convergence.
Thank you for your reply.

The file I uploaded is a pilot test with a low number of mesh to obtain the results quickly. So the the residuals did not converge. But I think it is enough to have a preliminary result. Further more, I have another calculation with a quite ideal convergence with 10^-5 residual.

The problem I met, is that I set the orifice inlet a mass flow rate(1.333e-3), and at the end of orifice, where is the interface with another domain, whose mass flow rate is 0! Other results is just as I expected, for example, the temperatture.

I have checked all the settings of my CFX Pre. But I cannot find the reason. Very gloomy.
Sataha is offline   Reply With Quote

Old   May 31, 2016, 12:27
Default
  #8
Senior Member
 
Join Date: Jun 2009
Posts: 1,369
Rep Power: 25
Opaque will become famous soon enough
It is very difficult to help w/o looking at some diagnostics, and with limited information.

Have you looked at the flow near the interface of concern ? If you have 50% flow in one direction, and 50% in the opposite, the net mass flow is still 0.

Have you look at the mass imbalances throughout the system? i.e. look at every interface downstream.

What do the streamlines from the inlet look like ?
Opaque is offline   Reply With Quote

Old   June 1, 2016, 02:10
Default
  #9
Senior Member
 
Maxim
Join Date: Aug 2015
Location: Germany
Posts: 410
Rep Power: 9
-Maxim- is on a distinguished road
Quote:
DOMAIN INTERFACE: Default Fluid Porous Interface
Boundary List1 = Default Fluid Porous Interface in fabric Side 1
Boundary List2 = Default Fluid Porous Interface in fabric backside Side \
2,Default Fluid Porous Interface in fabric front side Side 2
Are you sure that this is right? Fabric backside 2 and fabric front side 2 are on the same side? Maybe you can share some screenshots of the whole piece so that we know what flows where.

Otherwise Opaque is right: your residuals are still too high and your imbalances are not under 1% yet. Especially
Quote:
| P-Mass-fabric front | 2.6162E-05 | -1.4207% |
Those numbers should be way lower for an 'easy' case.

Maybe the number of iterations are not enough for the flow to "reach" the outlet. Streamlines can show you more
-Maxim- is offline   Reply With Quote

Old   June 16, 2016, 02:28
Default
  #10
New Member
 
Liang shuai
Join Date: Nov 2015
Posts: 13
Rep Power: 7
Sataha is on a distinguished road
Thank you all!

I have solved the problem. Actually, it is not solved, but searched in the site and I find a similar problem in:

http://www.cfd-online.com/Forums/cfx...-rate-cfx.html

The mass flow can not be observed at a certain point and it is have to be in a face at least.
Sataha is offline   Reply With Quote

Reply

Tags
impingement, mass flow rate

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Issues on the simulation of high-speed compressible flow within turbomachinery dowlee OpenFOAM Running, Solving & CFD 9 February 5, 2021 10:15
Mass flow rate boundary condition with negative values ashtonJ CFX 3 November 26, 2014 05:21
Convergence problem with target mass flow rate ADL FLUENT 2 May 29, 2012 21:11
mass flow Wenbin Song FLUENT 0 September 27, 2005 13:00
Mass Flow Inlet Pravir Kumar Rai FLUENT 0 February 19, 2003 14:03


All times are GMT -4. The time now is 16:27.