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31.5.3 Partitioning the Grid Automatically

For automatic grid partitioning, you can select the bisection method and other options for creating the grid partitions before reading a case file into the parallel version of the solver. For some of the methods, you can perform pretesting to ensure that the best possible partition is performed. See Section  31.5.5 for information about the partitioning methods available in FLUENT.

Note that if your case file contains sliding meshes, or non-conformal interfaces on which you plan to perform adaption during the calculation, you will need to partition it in the serial solver, and then read it into the parallel solver, with the Case File option turned on in the Auto Partition Grid panel (the default setting).

The procedure for partitioning automatically in the parallel solver is as follows:

1.   (optional) Set the partitioning parameters in the Auto Partition Grid panel (Figure  31.5.2) .

Parallel $\rightarrow$ Auto Partition...

Figure 31.5.2: The Auto Partition Grid Panel

If you are reading in a mesh file or a case file for which no partition information is available, and you keep the Case File option turned on, FLUENT will partition the grid using the method displayed in the Method drop-down list.

If you want to specify the partitioning method and associated options yourself, the procedure is as follows:

(a)   Turn off the Case File option. The other options in the panel will become available.

(b)   Select the bisection method in the Method drop-down list. The choices are the techniques described in Section  31.5.5.

(c)   You can choose to independently apply partitioning to each cell zone, or you can allow partitions to cross zone boundaries using the Across Zones check button. It is recommended that you not partition cells zones independently (by turning off the Across Zones check button) unless cells in different zones will require significantly different amounts of computation during the solution phase (e.g., if the domain contains both solid and fluid zones).

(d)   If you have chosen the Principal Axes or Cartesian Axes method, you can improve the partitioning by enabling the automatic testing of the different bisection directions before the actual partitioning occurs. To use pretesting, turn on the Pre-Test option. Pretesting is described in Section  31.5.5.

(e)   Click OK.

If you have a case file where you have already partitioned the grid, and the number of partitions divides evenly into the number of compute nodes, you can keep the default selection of Case File in the Auto Partition Grid panel. This instructs FLUENT to use the partitions in the case file.

2.   Read the case file.

File $\rightarrow$ Read $\rightarrow$ Case...

Reporting During Auto Partitioning

As the grid is automatically partitioned, some information about the partitioning process will be printed in the text (console) window. If you want additional information, you can print a report from the Partition Grid panel after the partitioning is completed.

Parallel $\rightarrow$ Partition...

When you click the Print Active Partitions or Print Stored Partitions button in the Partition Grid panel, FLUENT will print the partition ID, number of cells, faces, and interfaces, and the ratio of interfaces to faces for each active or stored partition in the console window. In addition, it will print the minimum and maximum cell, face, interface, and face-ratio variations. See Section  31.5.6 for details. You can examine the partitions graphically by following the directions in Section  31.5.6.

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