# Is this solution converged?

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May 17, 2018, 04:18
Is this solution converged?
#1
New Member

Michal Pacholczyk
Join Date: Sep 2016
Posts: 3
Rep Power: 7
Hi

This is simulation of wind tunnel nozzle. Boundary conditions as in given attachemtn? Can i consider this values of residuals as low enough since they are straight line? This is simulation with standard k-epsilon turbulance model.
Any ideas how to improve resiuadals? Do you think no slip wall outside of the nozzle is a good idea?
Attached Images
 contour.PNG (130.2 KB, 30 views) covergance.PNG (31.8 KB, 39 views)

 May 17, 2018, 10:27 #2 Member   Marcin Join Date: Jun 2016 Posts: 90 Rep Power: 7 Cześć Michał, There are several ways to assess convergence: - the level of residuals (for example 1e-3 for continuity, 1e-6 for energy) - mass and energy balance - tracking some monitor plot, for example area-weighted average of pressure

 May 17, 2018, 18:16 #3 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 4,776 Rep Power: 56 I would say they are. 1. Your contours look nice, meaning the initial condition seems to be gone. 2. Your residuals are flat/horizontal. Regardless of how high/low they are, the solution probably is not changing at all. Even if it is wrong or poor quality result, you probably cannot improve it anymore. I don't really care what is the magnitude unless it is 1000. But if it is 1e-03, 1e-05, does not make much difference. Anyway you know it will not go any lower than what it is. If you are not convinced. It is a good idea to verify the flow hasn't changed. You can make the same contour screenshot at different iterations and visually inspect. More quantitatively you make a point monitor or line monitor or surface monitor and check the any or all of the pressure, temperature, velocity, and so on and verify that nothing changes.

May 18, 2018, 05:26
#4
New Member

Michal Pacholczyk
Join Date: Sep 2016
Posts: 3
Rep Power: 7
hi Guys,

thanks you so much for help - actually i have changed all oustide nozzle boundaries to pressoure outlet and it has resulted in pretty nice convergance (as attached). Right now i am sure my solution is quiet ok with Y+ at wall in bound 13-22.

thanks
Attached Images
 covergance2.PNG (36.6 KB, 26 views)

 May 18, 2018, 15:04 #5 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 4,776 Rep Power: 56 Looks nice. # of cells with reversed flow not changing is also a reassuring indicator that the solution is converged (i.e. always 358 faces).