## 17.1. When to Use Expert Control Parameters

For a small number of cases, convergence difficulties can arise that cannot be resolved in the normal manner of time step control or judicious setting of initial values. Under these circumstances, modifying control parameters can help when all else fails to bring about a converged solution.

It should be emphasized that the most frequent requirement for access to expert control parameters is to take control of internal CFX-Solver defaults in order to improve or achieve convergence on a difficult case. Before you attempt to change expert control parameter settings, it is important that you have read through the advice section and have taken all the normal steps to address any convergence difficulties. Note that expert control parameters are only intended for use by customers who are experienced in using CFX, or who have been instructed to use expert control parameters by ANSYS customer support. Use of these parameters is not fully supported, and may cause unexpected or unintended consequences for both the performance of the CFX-Solver and the quality of the results.

Advice on flow modeling is available so that you can ensure you have done all that you can to obtain a converged solution before proceeding to modify expert control parameters. For details, see Advice on Flow Modeling.

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