Once you have initialized (or calculated) the entire flow field, you may patch different values for particular variables into different cells. If you have multiple fluid zones, for example, you may want to patch a different temperature in each one. You can also choose to patch a custom field function (defined using the Custom Field Function Calculator panel) instead of a constant value. If you are patching velocities, you can indicate whether the specified values are absolute velocities or velocities relative to the cell zone's velocity. All patching operations are performed with the Patch panel (Figure 25.14.2).
Solve Initialize Patch...
| When shell conduction is enabled, the names of the
Zones to Patch will appear as
shell:wall-name. The wall-name is the name of the wall on which a shell conduction zone has been created.
The ability to patch values in cell registers gives you the flexibility to patch different values within a single cell zone. For example, you may want to patch a certain value for temperature only in fluid cells with a particular range of concentrations for one species. You can create a cell register (basically a list of cells) using the functions that are used to mark cells for adaption. These functions allow you to mark cells based on physical location, cell volume, gradient or isovalue of a particular variable, and other parameters. See Chapter 26 for information about marking cells for adaption. Section 26.11.1 provides information about manipulating different registers to create new ones. Once you have created a register, you can patch values in it as described above.
Using Field Functions
By defining your own field function using the Custom Field Function Calculator panel, you can patch a non-constant value in selected cells. For example, you may want to patch varying species mass fractions throughout a fluid region. To use this feature, simply create the function as described in Section 30.5, and then perform the function-patching operation in the Patch panel, as described above.
Using Patching Later in the Solution Process
Since patching affects only the variables for which you choose to change the value, leaving the rest of the flow field intact, you can use it later in the solution process without losing calculated data. (Initialization, on the other hand, resets all data to the initial values.) For example, you might want to start a combustion calculation from a cold-flow solution. You can simply read in (or calculate) the cold-flow data, patch a high temperature in the appropriate cells, and continue the calculation.
Patching can also be useful when you are solving a problem using a step-by-step technique, as described in Section 25.22.2.