26.9 Initializing the Solution

Before starting your CFD simulation, you must provide ANSYS FLUENT with an initial "guess'' for the solution flow field. In many cases, you must take extra care to provide an initial solution that will allow the desired final solution to be attained. A real-life supersonic wind tunnel, for example, will not "start'' if the back pressure is simply lowered to its operating value; the flow will choke at the tunnel throat and will not transition to supersonic. The same holds true for a numerical simulation: the flow must be initialized to a supersonic flow or it will simply choke and remain subsonic.

There are two methods for initializing the solution:

• Initialize the entire flow field (in all cells).

• Patch values or functions for selected flow variables in selected cell zones or "registers'' of cells. (Registers are created with the same functions that are used to mark cells for adaption.)

Before patching initial values in selected cells, you must first initialize the entire flow field. You can then patch the new values over the initialized values for selected variables.