Convergence

The solution process in Creo Flow Analysis is iterative. You can limit the total number of iterations (global) for a steady simulation or total number of iterations per time step for a transient simulation by setting the converge criterion to the required convergence tolerance.

To modify the converge criterion, in the Flow Analysis Tree, under Physics select a module. Converge Criterion appears in the Properties panel.

When the correction for the module drops below its converge criterion, the code stops (steady) or moves to the next time step (transient) if the criteria for all other modules is reached.

Converge Criterion controls the convergence criterion for the Pressure and Velocity solutions. A smaller value of converge criterion implies more precision. The cost of a smaller value of converge criterion is more iterations, which result in more computation time. In some cases, the added accuracy is not worth the additional expense. If the target converge criterion is very small, you may not be able to achieve it. If this is the case then, the solution uses the full number of iterations.

The default converge criterion for a Transient simulation is 0.1 and for Steady state simulation is 0.001. These defaults usually provide sufficient accuracy. Higher convergence is required for Steady Simulations because the initial guess value is often further from the correct solution.

In cases where the solution is well converged, the residual may not drop. For example, for a transient simulation that converges to a steady solution, the solution at the beginning of each time step is sufficiently accurate so that the residual drop remains nearly constant. In such cases, you may want to use a larger and less stringent converge criterion. The Residual error drop for each active variable appears in the Residual panel. The scale for the Residual Drop is the exponent of the Residual, so that a drop of -three corresponds to a Converge Criterion of 0.001.

To view the residual panel, in the Flow Analysis tab, click XYPlot Panel.

The convergence parameters for the modules are as follows:

Convergence parameters | |

Module | Solution Variables (Residual Plot) |

Flow | Pressure, Velocity |

Turbulence | Turbulent Kinetic Energy and the Turbulent Energy Dissipation Rate |

Heat | Energy |