Fluid Flow Convergence Criteria

The nonlinear equations governing fluid flow are solved using an iterative solution method. Convergence refers to the point at which further iterations are no longer necessary. An important part of determining whether your solution is appropriate is to judge whether the solution has converged to an acceptable level.

By default, Discovery will automatically use a set of numerical convergence settings that are suitable in most cases. You can explicitly set the convergence criteria by going to Simulation Options in the ribbon of the Simulation tab and make modifications under Additional Fluid Flow Options. This option only affects solutions when in the Refine stage.

You can choose to determine the stopping criteria for when the problem has converged by selecting one of three options from the Stop on menu:

Engineering convergence: The engineering quantities of pressure, velocity, and temperature are monitored for each flow condition, and temperature and pressure are monitored for each wall condition. When these monitored quantities have stabilized, the solution will be determined as complete. This option is typically useful if these values are the primary focus of the solution and are unaffected by local areas of turbulent flow. If convergence is not achieved, the solution will stop when the Maximum number of iterations are reached, which can be adjusted in the Specify convergence settings, if required. Additionally, you can modify the Target engineering convergence tolerance to specify the level of convergence that you require.
Numerical convergence: Convergence is determined by examining differences throughout the fluid volume. This is useful if you are interested in the flow within the volume. To override the default values set by Discovery, select Specify convergence settings. Enter the Maximum number of iterations, if convergence is not met after this number of iterations, then the simulation will stop. Enter the Target numerical convergence to specify the difference for residual measurements (except energy) allowed between iterations, if the difference is below this level it will be considered as converged. Enter the Target numerical convergence, energy to specify the difference for energy allowed between iterations, if the difference is below this level it will be considered as converged.
Monitored value convergence: This is similar to engineering convergence, but will only use monitors of average values on the surfaces that you have defined. Under Specify convergence settings you can also modify Target convergence, monitors to specify the level of convergence that you require.