## 19.3. Setting the Solution Units

There are two sets of units in CFX-Pre: the units visible when selecting Edit > Options from the main menu, which are also used for mesh import and transformation, and the solution units set in the Solution Units details view (available from the main menu under Insert > Solver). The solution units are the units that the CFX-Solver writes in the results file. For details, see Units.

Setting the solution units does not alter the units you can use to define quantities in CFX-Pre. These are the units the results file is written in. Additionally, these are the units assumed in the summary at the end of the out file, when data such as variable range and forces on walls is presented.

When postprocessing a results file in CFD-Post, the units used are not necessarily those used in the results file. CFD-Post will convert to your preferred units.

Most common units can be used for the solution units; however, some important restrictions apply:

- The temperature solution units must be an absolute scale; for example, Kelvin [K] or Rankine [R]. Celsius and Fahrenheit cannot be used. Temperature quantities elsewhere in CFX-Pre can be set in Celsius and Fahrenheit.

- The solution units must not be changed when restarting a run. The units in the initial guess file will assume the units used in the current CFX-Solver definition (.def) file.

- You must not change the length units outside of CFX-Pre, for example, by editing the CCL in a CFX-Solver input file. The mesh is written to the CFX-Solver input file using the length units; therefore, once the CFX-Solver input file has been written, these units should not change.

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