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under-relaxation factors -> level of residuals

Posted August 27, 2012 at 09:27 by kira

more helpful info on under-relaxation factors:

Originally Posted by LuckyTran View Post
No magic here, that's what's supposed to happen. Unless your solution is diverging, do not bother with the under-relaxation factors. If it is diverging, do as you did, lower the factors until you can a stable solution, and then raise them again if possible. If not, then it is a hint that there is an inherent stability issues in the problem you are trying to solve or perhaps one of your modeling parameters is incorrect.

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what is under relaxation factor?

Posted August 27, 2012 at 09:23 by kira

something to keep in mind:
Originally Posted by Phil
Each of the variables(mass,mom,density) represents an equation the solver is trying to solve. Each iteration the values obtained for the variables should get closer and closer together - converge. FOR SIMPLE PROBLEMS ESPECIALLY COLD FLOWS WITHOUT COMBUSTION YOU SHOULD SIMPLY KEEP THE RELAXATION FACTORS AT DEFAULT.

Sometimes for many many reasons the solution can become unstable so a relaxation factor is used - takes part of value from previous iteration
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Useful Threads

Posted August 10, 2012 at 13:50 by lakeat (Daniel Wei's CFD Blog: (
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2D unstructured mesher in F90

Posted August 9, 2012 at 08:23 by truffaldino

This is 2D unstructured mesher.

tri_mesh.f90 is a mesher and the rest are input files

Example 1: Cavity flow driven by upper cavity wall

file: cavity_bc.txt

Example 2: flow past NACA 0012 airfoil

files: NACA0012_bc.txt - airfoil
wt_bc.txt - wind tunnel
wake_bc.txt -wake

Description of the program is placed in the header of tri_mesh.f90
Attached Files
File Type: f tri_mesh.f (100.5 KB, 359 views)
File Type: txt cavity_bc.txt (65 Bytes, 227 views)
File Type: txt NACA0012_bc.txt (16.6 KB, 324 views)
File Type: txt wt_bc.txt (184 Bytes, 237 views)
File Type: txt wake_bc.txt (5.5 KB, 340 views)
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