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problem with convergence

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Old   November 11, 2015, 15:17
Default problem with convergence
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Reza Rohani
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I'm new to fluent. I want to simulate a rectangular nozzle in 2D. Wondering when I use mesh NO.1 it converges properly after 17500 iterations, but in mesh NO.2 when I refine it near throats and cavities even without add boundary layer, residuals oscillate and it doesn't converge after 270k iterations.

I really appreciate it if anyone could help, Thanks in advance.
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Old   November 12, 2015, 00:49
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What do your mesh metrics say?

It looks like there's too rapid area/volume change in the regions where you refined the grid, especially at the outlet. Keep your volume change <33% or so between adjacent cells.

But also check your skewness. It's hard to tell if the skewness was worse the refined grid in the picture.
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Old   November 12, 2015, 17:05
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Quote:
Originally Posted by LuckyTran View Post
What do your mesh metrics say?

It looks like there's too rapid area/volume change in the regions where you refined the grid, especially at the outlet. Keep your volume change <33% or so between adjacent cells.

But also check your skewness. It's hard to tell if the skewness was worse the refined grid in the picture.
thanks LuckyTran for reply & guidance. how can I keep my volume change under 33% in gambit. I doubt my grid ratio on edges were high, they are 1.07 and 1.05 on edges. Should I decrease number of interval counts?
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convergence, fluent, nozzle, nozzle simulation, oscillating residuals

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