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-   -   Time step continuity error (http://www.cfd-online.com/Forums/openfoam-solving/111324-time-step-continuity-error.html)

Alish1984 January 3, 2013 14:21

Time step continuity error
 
Hi

I have some clear questions? I wonder if someone can reply clearly too ;)

1-is time step continuity error really important in steady solvers including energy eq.?
2-what about unsteady ones that use piso?
3-if the answer is yes what should be the order of a-sum local, b-global c-cumulative continuity errors?

adambarfi January 4, 2013 06:19

see these posts:

http://www.cfd-online.com/Forums/ope...t-meaning.html

http://www.cfd-online.com/Forums/ope...ity-error.html

Alish1984 January 5, 2013 11:35

Quote:

Originally Posted by adambarfi (Post 400065)

I have read the source of compressibleContinuityErrs.H and have seen in such a strange manner the continuity is checked. one of my questions was "is it realy important in steady solvers?"
as u can see in "rhoPimpleFoam" tutorial case "angleduct"after 10 step it has:

sum local=0.000953371, global=0.000776714, cumulative=0.402763

Aadhavan January 5, 2013 13:00

Hi There,
I am also getting the same problem, here is some data. I really dont know how to solve this problem. I am using MRFSimpleFoam
Time = 31
time step continuity errors : sum local = 0.00425606, global = 0.000924716, cumulative = 0.0274701

Time = 32
time step continuity errors : sum local = 0.00357216, global = 0.000535369, cumulative = 0.0280054

Time = 33
time step continuity errors : sum local = 0.00360527, global = -0.000591305, cumulative = 0.0274141

Time = 34
time step continuity errors : sum local = 0.00362457, global = -0.000742113, cumulative = 0.026672

Time = 35
time step continuity errors : sum local = 0.00331502, global = -0.000725819, cumulative = 0.0259462

Time = 36
time step continuity errors : sum local = 0.00305899, global = 0.000333275, cumulative = 0.0262795

Time = 37
time step continuity errors : sum local = 0.0030778, global = 0.000586366, cumulative = 0.0268658

I have gone through the link which you have given to alish1984 and so many other post as well. Now I came to know, its is important as well it is something to do with pressure solver.
I changed relTol to 0 then there where no problem, but its taking lot of time to solve pressure (for one time step 10 to 15 min)
the above data is for relTol = 0.0005 in fvSolution --> pressure

adambarfi, if you are able to explain how to solve it, I will be grateful to you.

Thanks in advance,
Aadhavan


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