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 aqib February 4, 2011 05:16

convergence criteria

hi all users,
i am running an unsteady case of Cascade T106A. It is a bounded flow.
i want to ask what convergence criteria i have to used?
Mass flow rate will be ok or not?
any guide line for me please?
Regards:
Aqib

 -mAx- February 4, 2011 05:36

I would uncheck convergence criteria
Just let iterate and monitor any quantity yu are interested (for instance massfow)

 aqib February 4, 2011 08:24

i am interested in the co-efficient of loss pressure in which i have to compared my case with some other case.....
should i iterate both cases to the same number of iterations?
secondly, in "the co-efficient of loss pressure" formula there is a quantity of "inlet stagnation pressure" which varied after every 500 iterations....
so what does it means?
which value i have to be used?

 -mAx- February 4, 2011 08:41

what is co-efficient of loss pressure?

 aqib February 4, 2011 09:13

The total pressure loss coefficient
ω=(Pt(inlet)-Pt(outlet))/q(inlet)
inlet where ω is the total pressure loss coefficient, Pt is the stagnation pressure, and q(inlet) is the dynamic pressure at the inlet

 aqib February 4, 2011 09:14

in my case dynamic pressure at inlet(q) remains same but both the stagnation pressure at inlet and outlet varied with number of iterations

 -mAx- February 4, 2011 09:44

Then you didn't reach convergence.
Let iterate untill you get constant values

 aqib February 7, 2011 02:32

my solution is converged but it is periodically converged....that's why the values are varying with the iterations.....:)

 -mAx- February 7, 2011 03:08

Sorry I just checked, that you are working with unsteady solver.
Is your monitoring x-axis iterations or time step? (post a picture)
I cannot remember if you can choose between iterations and time step in the monitoring panel (for unsteady solver).

 aqib February 7, 2011 08:37

1 Attachment(s)
attaching the picture of inlet and outlet stagnation pressure

 -mAx- February 8, 2011 02:05

I don't think this is an absolute convergence monitoring, but unsteady monitoring.
If I am right you can see, the "convergence" (especially in the left chart), it looks like stairs.
Each stair represents a convergence loop.
To be sure, just increase the max iterations per time step, and replot: the stairs should be stretched.

 aqib February 8, 2011 05:25

so its mean my solution is converged?

 -mAx- February 8, 2011 05:49

if the "stairs" are stretched while you increased the max iteration/time step, then your solution converged for each time step

 aqib February 8, 2011 06:30

thanks yes it is visualize to me....
solution is converged....:)

 arunintn March 7, 2012 05:41

Divergence detected in AMG solver: temperature

Hi,
I doing the cascade and i'm new to CFD. I like to know what are the input values i need to have with me before i start fluent. I just finished the gambit and now waiting for solution.

My case is 2D. I using K-omega SST. I'm pleased if some one help me about the steps i need to follow to solve.

(I had the same problem "Divergence detected in AMG solver: omega" i changed URF to F-cycle.)

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