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4.3.4 Automatic Saving of Case and Data Files

You can request FLUENT to automatically save case and data files at specified intervals during a calculation. This is especially useful for time-dependent calculations, since it allows you to save the results at different time steps or flow times without stopping the calculation and performing the save manually.

You can also use the autosave feature for steady-state problems, to examine the solution at different stages in the iteration history. Automatic saving is specified using the Autosave Case/Data panel (Figure  4.3.1).

File $\rightarrow$ Write $\rightarrow$ Autosave...

Figure 4.3.1: The Autosave Case/Data Panel

You must set the frequency of saves for case and/or data files, and the root file name. Enter the case-saving frequency in the Autosave Case File Frequency field, and the data-saving frequency in the Autosave Data File Frequency field. Both values are set to zero by default, indicating that no automatic saving is performed.

For steady flows, you can specify the frequency in iterations, and for unsteady flows, you can specify it in time steps or flow time (unless you are using the explicit time stepping formulation, in which case you specify the frequency in iterations). If you define an Autosave Case File Frequency of 10, for example, a case file is saved every 10 iterations or time steps.

If you have limited disk space, restrict the number of files saved by FLUENT using the Overwrite Existing Files option. Enable the Overwrite Existing Files option and set the value of the Maximum Number of Each File Type field. The case and data files are treated separately. For example, if the value of Maximum Number of Each File Type is set to five, FLUENT saves a maximum of five case and five data files, irrespective of the frequency. After saving the specified number of files, FLUENT overwrites the earliest existing file. For steady-state calculations, the saved file name that you enter in the File Name field will have an iteration appended to it.

For unsteady-state calculations, you can autosave files such that your file name has a flow time or time step appended to it. You can select time-step or flow-time from the Append File Name with drop-down list (see Figure  4.3.2).

Enter the file name for the autosave files in the File Name field. The iteration or time-step number and an appropriate suffix ( .cas or .dat) is added to the specified root name. If the specified File Name ends in .gz or .Z, appropriate file compression is performed. See Section  4.1.5 for details about file compression.

Consider an unsteady-state case for which you want to save your case and/or data files at known time steps. The procedure you would follow is to first set a frequency for the Autosave Case/Data File Frequency field. Select time-step from the Append File Name with drop-down list. The resulting files saved would be

indicating that this file was saved at the fifth time step.

If you want to save your case and/or data files at known flow times, select flow-time from the Append File Name with drop-down list. The default No. of Decimal Digits in File Name will be six, however, you can modify this number to reduce or increase the width of your file name. Enter a file name ( myfile) in the File Name field. The resulting files saved are


indicating a flow time of 0.5 seconds.

Figure 4.3.2: The Autosave Case/Data Panel when Appending flow-time

For steady-state and unsteady-state cases, you have the option to specify the format in which you want to save your case and/or data files. For example, you may want to save your solutions at certain flow times with their corresponding time steps (transient cases only). Select time-step from the Append File Name with and enter the File Name followed by a -%f, indicating the flow time as described in Section  4.1.7.

For example, entering filename-%f will result in the saved file name having the format filename-000.500000-0010.cas. The naming convention used in the example ( filename-000.500000-0010.cas) can be explained as follows:

All of the autosave inputs are stored in the case file.


The automatic numbering of files can be applied when using the autosave function. Section  4.1.7 has information on automatic numbering of files.

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