# problem with convergence

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November 11, 2015, 15:17
problem with convergence
#1
New Member

Reza Rohani
Join Date: Apr 2015
Posts: 7
Rep Power: 11
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.
Attached Images
 1.jpg (106.1 KB, 13 views) 2.jpg (111.2 KB, 10 views)
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 November 12, 2015, 00:49 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,699 Rep Power: 66 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.

November 12, 2015, 17:05
#3
New Member

Reza Rohani
Join Date: Apr 2015
Posts: 7
Rep Power: 11
Quote:
 Originally Posted by LuckyTran 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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Knowledge is power and it can command obedience. Remember that knowledge is a ruler and wealth is its subject. The Peak of Eloquence, Saying 146

 Tags convergence, fluent, nozzle, nozzle simulation, oscillating residuals