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

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

thanks for replying....
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?

what is co-efficient of loss pressure?

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

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

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

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

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).

attaching the picture of inlet and outlet stagnation pressure

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.

so its mean my solution is converged?

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

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

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.)