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-   -   low local continuity while high global continuity (http://www.cfd-online.com/Forums/openfoam-solving/119356-low-local-continuity-while-high-global-continuity.html)

immortality June 15, 2013 10:19

low local continuity while high global continuity
 
what does low local continuity residual(1e-5)but high global(1e-18)mean?
Code:

DILUPBiCG:  Solving for Ux, Initial residual = 0.0004256482273, Final residual = 3.42419877e-17, No Iterations 4
DILUPBiCG:  Solving for Uy, Initial residual = 0.0008584110976, Final residual = 1.699508551e-16, No Iterations 4
DILUPBiCG:  Solving for e, Initial residual = 0.0004690168561, Final residual = 4.48278334e-17, No Iterations 4
DILUPBiCG:  Solving for p, Initial residual = 0.0004642938087, Final residual = 8.887120082e-17, No Iterations 4
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 4.223753118e-06, global = -9.485719823e-18, cumulative = -4.473784803e-05
DILUPBiCG:  Solving for p, Initial residual = 3.306483671e-07, Final residual = 6.449921349e-17, No Iterations 3
diagonal:  Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0
time step continuity errors : sum local = 4.21218922e-06, global = -9.149711212e-18, cumulative = -4.473784803e-05
DILUPBiCG:  Solving for omega, Initial residual = 0.0003045968168, Final residual = 4.305610069e-16, No Iterations 4
DILUPBiCG:  Solving for k, Initial residual = 0.0008443110421, Final residual = 9.851206562e-18, No Iterations 5

what does it indicate for?:confused:

wyldckat June 16, 2013 09:12

Hi Ehsan,

Quote:

low local continuity residual(1e-5)but high global(1e-18)
Uhm... isn't it the other way around? Low global and high local?

Almost a month ago, you had asked me about adding continuity to rhoCentralFoam. In one of the emails, I had sent the following explanation:
Quote:

OK, from what I could figure out, the following code is needed:
  • #include "initContinuityErrs.H" //this is to be placed before the "while" loop
  • #include "compressibleContinuityErrs.H" //this is found in the "pEqn.H" file, after including "rhoEqn.H"
The two files are located at OpenFOAM's "src/finiteVolume/lnInclude/" folder.
Have a look into the file "$FOAM_SRC/finiteVolume/lnInclude/compressibleContinuityErrs.H" to see how it's calculated.

Best regards,
Bruno

immortality June 16, 2013 09:32

Hi Bruno
I meant the accuracy.local has low accuracy.maybe wasn't careful enough!
rhoCentralFoam hasn't any difficulty in relation to continuity.both local and global continuity residuals are low enough,these results are from sonicFoam.

wyldckat June 16, 2013 12:25

rhoCentralFoam does things in a very different way, at least from what I've vaguely read about it. If I'm not mistaken, it tends to smooth out the values (because it's "central", it takes into account more values from it's sides and the previous times?), which would be why the continuity would be well preserved.

But sonicFoam doesn't have this feature that rhoCentralFoam has got, which is probably why you're seeing larger continuity issues. Try reducing the "deltaT", to see if it has any effect. If it doesn't, then "fvSchemes" and the mesh itself should perhaps be the ones to blame?


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