I am using FLUENT to calculation airflow with standard two equation model. The plot of the residual has reduced to 10e-4. However, suddely, the residual of the variables has gone up to 10e-1. I cannot quite understand this. Does that mean the results are not converged? why is it happen?

Thanks

in fluent with two equation models it could some times happen because of the coupling of the two variables (k and e or k and omega), to check this run the calculationsd with out turbulence model and if you get converged solution, then for the two turbulence quantites, go to multigrid control and change the pre sweeps to 1 (default is 0) and make post sweeps to 2 (default is 1) and if u r getting warning of turbulent viscosity limited etc when u start the calculations, then restrict the viscosity ratio to some low value say 100, till you start to get convergence with the two turbulence quantitities and then slowly remove the restriction from viscosity ratio.

this should work fine.

Thanks for the detailed information