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 May 24, 2001, 23:24 about residuals in fluent #1 Devy Guest   Posts: n/a Hi, Now I am simulating gas flow in a tube I use couple solver implicit ,ideal gas model, second upwind.I define the courant number as 0.5. I find the residuals sometims increase,sometimes decrease.When I change to first upwind,the same problem is still unsolved. How can I solve this problem? Would you give me some advice? Thank you. Any answer will be welcome. Devy 2001.5.25

 May 25, 2001, 22:19 Re: about residuals in fluent #2 Devy Guest   Posts: n/a Hi,Mr Sundar: Thank you for your reply. Now I am simulating gas flow in a tube I use couple solver implicit ,ideal gas model, second upwind,three mass-inlets(subsonic),one pressure-out(supersonic),and other wall boundary.I define the courant number as 0.5. I find the residuals sometims increase,sometimes decrease.When I change to first upwind,the same problem is still unsolved. When I check mass flow rate,I find the value of massinet is bigger the value I input and all of mass flow rate of the inlet and outlet is less then 0.The value of residuals is about 1.2e-1. Thank you. Devy 2001.5.26

 May 28, 2001, 18:37 Re: about residuals in fluent #3 Kuochen Guest   Posts: n/a You should check mass flux instead of mass flow-rate. Flux calculation is based on face values instead of cell value, therefore gives you exactly what was input at the inlet boundary.

 June 8, 2001, 00:25 Re: about residuals in fluent #4 Chetan Kadakia Guest   Posts: n/a How have you adjusted your under-relaxation factors? I start them low (maybe 0.1) and then when I notice steady convergence I increase the factors a little bit. What about your initial conditions and boundary conditions. I find that if one thing isn't defined improperly (improperly in respect to Fluent), the solution blows up.

 June 9, 2001, 07:18 Re: about residuals in fluent #5 Devy Guest   Posts: n/a Hi, Thank you for your reply. I am using couple implicit model.there is notunder-relaxation factors.I think I define the correct initial conditions and boundary conditions. Thank you Devy 2001.6.9

 June 11, 2001, 00:50 Re: about residuals in fluent #6 Kuochen Guest   Posts: n/a You can still adjust the courant number with the implicit coupled solver. The default value is 5. Make to 0.1, for example, and run it for a while, then try to increase the value to 1.0 and so on.