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Odd residuals plot using NITA

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Old   January 7, 2016, 08:24
Default Odd residuals plot using NITA
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Mark Schulte
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Hello everyone, I am modeling a simple system of water flowing down a vertical surface. (I think it is funny what some people in some forums call a simple system...) I am tracking the wavy gas/liquid interface using VOF. Recently I start using Non-iterative Time Advancement (NITA) which solves faster than without, even with time steps that are small by an order of magnitude. However, it give odd residuals plots sometimes and I don't know if there is something wrong. The interface looks sharp, shaped as I expected, the solution progresses and most of the time it looks like:

NITA normal.png

However, every once in a while I look at the residuals and they look like:

NITA odd.png

the solution doesn't crash and progresses as normal. Do I need to be worried? Is it just that Fluent is only storing a certain amount of residuals and clears it every once in a while?

Any help is much appreciated.
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Old   January 8, 2016, 00:02
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IF it is transient, that is what the residuals will look like.
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free surface, multiphase unsteady, nita, residuals, vof

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