[riteshnw]

Hi all.
I am doing a simulation on a real scale cuboidal building with small extrusion at the entrance (canopy) and it is inclined at 3 degrees. I performed the simulation in Ansys fluent and the simulation is not reaching at the convergence.

The minimum element quality is 0.64, minimum orthogonal quality of mesh is 0.71 and max skewness is 0.55. I used the proximity size function and cutcell as assembly meshing and mesh seems to be good and there are about 3.76 million elements and 4.05 million nodes.
I am using standard k-epsilon turbulence model with inlet velocity as 12 m/s and outlet as pressure outlet.

I am using pressure-velocity coupling as SIMPLE and all the parameters of spatial discretization as first order upwind to initialize the solution. The URFs are default and I tried changing them to 0.2 for pressure and 0.5 for other parameters. I set the residuals at 1*10^-4 and initialize the solution from inlet and then started the steady state simulation.

I tried changing the URFs, orders of the simulations, initialization properties. But, I do not understand the problem why the simulation is not getting converged. The minimum residual value it reaches for continuity is 4.75*10^-2 and after that it changes the value around this value and residual plot stays stable.

Can anyone please help me?

[jsm]

Hello,

Some times, residual monitors won't converge to 1e-6 and it will become flat. If simulation monitors are flat, then it doesn't mean that solution is not converged.

You have add some monitor points like pressure and velocity at critical locations before start the calculation. If monitor points become steady or oscillating (in repeated pattern) with respect to iteration, then simulation can be taken as converged.

[riteshnw]

Dear JSM,
Thank you for your reply.
So it means that I will have the solution with the magnitude 4*10^-2 error.
Is that correct?

Ritesh

[jsm]

No. If initial solution is so close to final solution, then residual convergence will be low and become flat. That is the reason, always we have to monitor some parameters like pressure or velocity etc., to check the convergence.

Only residual convergence is not sufficient to tell the results are accurate. You have to check Reports-->Fluxes-->Mass flow rate between inlet and outlet. Flux convergence & monitor points will give convergence level of the solution accurately than residual monitors.

[riteshnw]

Dear JSM,

Thank you.
I will try the simulation using the monitors plot for mass imbalance, average pressure and average velocity and I will let you know the results.
I hope it will work.

Kind regards,
Ritesh

[riteshnw]

Dear JSM,
I performed the si,ulation. I started the simulation with first order upwind and when the residuals and other monitor parameters were stable, I continued with second order upwind and after that I reduced the URFs.
The mass flow rate and mass imbalance seemed constant throughout the simulation bu there were some up and down variations in avg. pressure and avg. velocity.
Please find the images in attachment and let me know if they can be considered as good solution.
Thank you in advance.

Ritesh