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

Mass Flow Residual Convergence Problem

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

Like Tree1Likes
  • 1 Post By MKuhn

Reply
 
LinkBack Thread Tools Display Modes
Old   November 5, 2017, 18:13
Unhappy Mass Flow Residual Convergence Problem
  #1
New Member
 
Tosbaga's Avatar
 
Tosbaga
Join Date: Mar 2017
Location: Earth
Posts: 6
Rep Power: 2
Tosbaga is on a distinguished road
Hello Everyone,

I am currently trying to simulate a wind tunnel experiment with a Delta wing inside it. The problem is with the mass residual which i cannot drop it below an order of E-4. The other residuals are converging nicely.

I have used an adequate mesh with the following qualities,

Max Skewness : 0.86,
Max Aspect Ratio : 56,
Min Orthogonal Quality : 0.13

I am confident that the element size is suitable for my simulation. I am using PBCS with a SST k-w turbulence model, Inflations layers are produced with a first layer thickness which will produce a y+ value of ~1.

Computational domain consist of a Velocity inlet, Pressure outlet,Symmetry, Wind tunnel walls and delta wing as wall also.

I have tried to lower the relaxation factors as well but it didnt cause any significant effect on the mass residual.

I am also monitoring the Cl and Cd coefficients and after 2000 iterations they do not change. I also checked the mass flux difference between inlet and outlet an its of order E-9 close to zero too but I feel like I cannot rely on the solution because of the mass residual.

Do i miss something i dont know. Help would be much appreciated.

Thanks in advance.
Regards,
Tosbaga is offline   Reply With Quote

Old   November 6, 2017, 02:59
Default
  #2
New Member
 
Moritz Kuhn
Join Date: Apr 2010
Location: Dresden
Posts: 25
Rep Power: 9
MKuhn is on a distinguished road
Why you would like to reach a residual for the mass lower than 1E-3, which is the default value and for the most cases fully sufficient, as you can see on your mass flux balance?
Keep in mind that the flow in your steady state case could have a little transient, time dependent character, that could be the reasen for not lowering the mass residual further.
Tosbaga likes this.
MKuhn is offline   Reply With Quote

Old   November 6, 2017, 12:49
Default
  #3
New Member
 
Tosbaga's Avatar
 
Tosbaga
Join Date: Mar 2017
Location: Earth
Posts: 6
Rep Power: 2
Tosbaga is on a distinguished road
Quote:
Originally Posted by MKuhn View Post
Why you would like to reach a residual for the mass lower than 1E-3, which is the default value and for the most cases fully sufficient, as you can see on your mass flux balance?
Keep in mind that the flow in your steady state case could have a little transient, time dependent character, that could be the reasen for not lowering the mass residual further.
Thanks for the answer, I am not an expert in CFD area however, in most of the cases I have seen, I learned that the mass flow residual should at least be under E-5 and the same recommendation is also available in FLUENT best practices document too.

I have considered unsteadiness but there is none in my case. Could you recommend some other suggestion ?

Regards.
Tosbaga is offline   Reply With Quote

Old   November 7, 2017, 08:39
Default
  #4
New Member
 
Moritz Kuhn
Join Date: Apr 2010
Location: Dresden
Posts: 25
Rep Power: 9
MKuhn is on a distinguished road
Sorry no more hints. It depends also what for a precision do yo need. Normally I have with 1E-3 for the mass residual good consonance betwenn simulation and reality.

Moritz
MKuhn 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
Free surface issues with interDyMFoam for hydroturbine oumnion OpenFOAM Running, Solving & CFD 0 October 6, 2017 14:05
chtMultiRegionSimpleFoam turbulent case Aditya Patil OpenFOAM Running, Solving & CFD 6 April 24, 2017 22:13
pressure in incompressible solvers e.g. simpleFoam chrizzl OpenFOAM Running, Solving & CFD 13 March 28, 2017 05:49
Problem with chtMultiregionFoam radiation boundary condition baran_foam OpenFOAM Running, Solving & CFD 9 September 4, 2015 07:31
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20


All times are GMT -4. The time now is 09:21.