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6.8.10 Scaling the Grid

Internally, FLUENT stores the computational grid in meters, the SI unit of length. When grid information is read into the solver, it is assumed that the grid was generated in units of meters. If your grid was created using a different unit of length (inches, feet, centimeters, etc.), you must scale the grid to meters. To do this, you can select from a list of common units to convert the grid or you can supply your own custom scale factors. Each node coordinate will be multiplied by the corresponding scale factor.

Scaling can also be used to change the physical size of the grid. For instance, you could stretch the grid in the $x$ direction by assigning a scale factor of 2 in the $x$ direction and 1 in the $y$ and $z$ directions. This would double the extent of the grid in the $x$ direction. However, you should use anisotropic scaling with caution, since it will change the aspect ratios of the cells in your grid.

figure   

If you plan to scale the grid in any way, you should do so before you initialize the flow or begin calculations. Any data that exist when you scale the grid will be invalid.

You will use the Scale Grid panel (Figure  6.8.10) to scale the grid from a standard unit of measurement or to apply custom scaling factors.

Grid $\rightarrow$ Scale...

Figure 6.8.10: The Scale Grid Panel
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Using the Scale Grid Panel


The procedure for scaling the grid is as follows:

1.   Indicate the units in which you created the grid by choosing the appropriate abbreviation for centimeters, millimeters, inches, or feet in the Grid Was Created In drop-down list. The Scale Factors will automatically be set to the correct values (e.g., 0.0254 meters/inch or 0.3048 meters/foot). If you created your grid using units other than those in the list, you can enter the Scale Factors (e.g., the number of meters per yard) manually.

2.   Click on the Scale button. The Domain Extents will be updated to show the correct range in meters. If you prefer to use your original unit of length during the FLUENT session, you can follow the procedure described below to change the unit.

Changing the Unit of Length

As mentioned above in step 2, when you scale the grid you do not change the units; you just convert the original dimensions of your grid points from your original units to meters by multiplying each node coordinate by the specified Scale Factors. If you want to work in your original units, instead of in meters, you can click on the Change Length Units button. This is a shortcut for changing the length unit in the Set Units panel (see Section  5.4). When you click on the Change Length Units button, the Domain Extents will be updated to show the range in your original units. This unit will be used for all future inputs of length quantities.

Unscaling the Grid

If you use the wrong scale factor, accidentally click the Scale button twice, or wish to undo the scaling for any other reason, you can click on the Unscale button. "Unscaling'' simply divides each of the node coordinates by the specified Scale Factors. (Selecting m in the Grid Was Created In list and clicking on Scale will not unscale the grid.)

Changing the Physical Size of the Grid

You can also use the Scale Grid panel to change the physical size of the grid. For example, if your grid is 5 feet by 8 feet, and you want to model the same geometry with dimensions twice as big (10 $\times$ 16), you can enter 2 for the X and Y Scale Factors and click on Scale. The Domain Extents will be updated to show the new range.


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