21.1.2 Solution Strategies

To solve for NOx products, perform the following steps:

• (optional) If the discrete phase model (DPM) is activated (by turning on the Interaction with Continuous Phase) to run with the NOx model, then set the Number of Continuous Phase Iterations per DPM Iteration to 0 such that no DPM iterations are performed as the NOx case is being solved.

• In the Equations dialog box of the Solutions Controls task page, turn off the solution of all variables except species NO (and HCN, NH $_3$, or N $_2$O, based on the model selected).

  Solution Controls Equations...

• Also in the Solution Controls task page, set a suitable value for the NO (and HCN, NH $_3$, or N $_2$O, if appropriate) under-relaxation. A value of 0.95 is suggested, although lower values may be required for certain problems (i.e., if convergence cannot be obtained, try a lower under-relaxation value).

• In the Residual Monitors dialog box, decrease the convergence criterion for NO (and HCN, NH $_3$, or N $_2$O, if appropriate) to $10^{-6}$.

  Monitors Residuals Edit...

• Perform calculations until convergence (i.e., until the NO (and HCN, NH $_3$, or N $_2$O, if solved) species residuals are below $10^{-6}$) to ensure that the NO and HCN or NH $_3$ concentration fields are no longer evolving.

  Run Calculation

  When you begin iterating with the NOx model enabled, ANSYS FLUENT may report that the solution has converged after the first iteration. This is due to the lack of significant levels of pollutants in the solution. You can force ANSYS FLUENT to continue iterating by repeated iteration requests. Once pollutants appear in the solution, ANSYS FLUENT will continue iterating on its own until a steady solution is achieved.