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-   -   multi block error (http://www.cfd-online.com/Forums/flow-3d/95222-multi-block-error.html)

ava December 10, 2011 02:35

multi block error
 
dear all
i work in a model with multi block method
but i dont know why the multi block error(mlbk error) is so great?

MuxaB December 12, 2011 01:43

you mean volume error? The error is computed by comparing the flow rate on each side of an inter-block boundary and summing it over all inter-block boundaries.

The error would be non-zero if the flow rate do not match, and may be more so if any of the following is happening:

1. large change in mesh resolution between adjacent mesh blocks
2. significant fluid break up at the boundary
3. poor convergence of the pressure solver

What version are you running? There is also ain input variable called inter-block boundary interpolation coefficient whose value varies from 0 to 1, with the default value of 0.25. You may want to raise it to get volume conservation.

ava December 12, 2011 02:16

question
 
hi and thanks
my software version is 9.3
in iran i couldn't find 9.4 version of it:(
where is inter-block boundary interpolation coefficient
is necessary to check it?
what is the allaowable limitation of it?
ava
whit the best regards:)

MuxaB December 12, 2011 12:06

it's under Numerics > Convergence Controls for pressure solvers, at the very bottom. If you did not change it, it must be at the default, which usually works fine. When it is =0, the coupling between blocks is done only through pressure, when it is =1 - through velocity. The default of 0.25 means 25% velocity and 75% pressure.


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