problem with convergence

rohani · November 11, 2015, 16:17

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.

LuckyTran · November 12, 2015, 01:49

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.

rohani · November 12, 2015, 18:05

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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November 12, 2015, 01:49		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 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.