KR132: How can I improve the convergence of FLUENT calculations involving combustion and radiation?
Steady state calculations are independent of the initial condition specified. However, the use of combustion and/or radiation models introduces significant nonlinearities in the transport equations and a poor initial condition may even cause divergence of the solution. To enhance solver robustness and stability and decrease overall solution turnaround times, here is a suggested solution procedure: To start with, run the calculation with only the flow equations turned on (cold flow solution) for about 100 iterations or so until the solution shows reasonable convergence. In this step, use the "Solution Controls" GUI panel (Solve>Controls>Solution...) to activate or deactivate equations. Next, activate the calculation of the energy equation as well as the species equations (or the PDF equation if you are using the PDF combustion model). Include the calculation of discrete phase particles (if any). After obtaining a converged solution with all of the above, finally include the radiation model and converge to the final solution. 

