about residuals in fluent
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 
Re: about residuals in fluent
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 massinlets(subsonic),one pressureout(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 1.2e1. Thank you. Devy 2001.5.26 
Re: about residuals in fluent
You should check mass flux instead of mass flowrate. Flux calculation is based on face values instead of cell value, therefore gives you exactly what was input at the inlet boundary.

Re: about residuals in fluent
How have you adjusted your underrelaxation 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.

Re: about residuals in fluent
Hi,
Thank you for your reply. I am using couple implicit model.there is notunderrelaxation factors.I think I define the correct initial conditions and boundary conditions. Thank you Devy 2001.6.9 
Re: about residuals in fluent
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.

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