Selecting the Automatic option allows the solver to automatically read the initial conditions from an initial values file if it can find one, or else use a solver default initialization field if no initial values file is provided. If the default initialization field is used, the CFX-Solver will calculate values for the solved variable at the start of the solution. You can select an initial values file for the CFX-Solver to use from the CFX-Solver Manager or from the Run Definition tab for a simulation execution control or a configuration in CFX-Pre. For details, see Reading the Initial Conditions from a File.

Choosing the Automatic option without providing an initial values file is only recommended for steady-state runs. For transient runs, you should provide initial conditions that correspond to the real flow field at the start of the calculation, and the CFX-Solver will stop by default if it has to use a solver default initialization field for a transient run for any quantities except turbulence-related variables.

If the automatic initial guess fails, it is often because an inappropriate initial velocity or static pressure field exists. Poor initial guesses are one of the most common reasons for the CFX-Solver to fail. If you use Automatic as the initial guess method for velocity, you must understand how the initial guess field is generated in CFX-Solver; this is described below. You should think about an initial guess and use the Automatic with Value option to set a constant value for velocity and pressure if the Automatic option is inappropriate. Better still, use CEL expressions or Cloud Interpolation to initialize the velocity and pressure fields.

An automatic initial guess is always acceptable for incompressible laminar cases if a sensible velocity field is produced, as described below. It is sometimes acceptable for incompressible turbulent cases, but the Automatic with Value method is often better.

Additional information on the way in which the Automatic option calculates values, and on sensible values for initial guesses, is available in Initialization Parameters.