There
are no universal metrics for judging convergence. Residual definitions that are
useful for one class of problem are sometimes misleading for other classes of
problems. Therefore it is a good idea to judge convergence not only by
examining residual levels, but also by monitoring relevant integrated quantities and checking for mass and energy balances.
There
are three indicators that convergence has been reached:
- The residuals have decreased to a sufficient degree. The solution has converged when the Convergence Criterion for each variable has been reached. The default criterion is that each residual will be reduced to a value of less than 1e-3, except the energy residual, for which the default criterion is 1e-6.
- The solution no longer changes with more iterations. Sometimes the residuals may not fall below the convergence criterion set in the may show that the residuals have stagnated and do not change with further iterations.This could also be considered as convergence.
- The overall mass, momentum, energy, and scalar balances are obtained. You can examine the overall mass, momentum, energy and scalar balances in the Flux Reports dialog box. The net imbalance should be less than 0.2% of the net flux through the domain when the solution has converged. In the next step you will check to see if the mass balance indicates convergence.
