Editing the CFD Grid

As soon as a new analysis data set has been created, a default CFD grid is generated using the default grid spacing defined as part of the data set. The default grid may be edited using the ‘Edit CFD Grid’ tool which allows you to change the spacing used for default regions, insert additional regions or remove previously inserted regions.

When you select the ‘Edit CFD Grid’ tool, the grid is displayed with the building outline overlaid as a ghosted wire frame. Grid regions are displayed along the major axes bounded by dark grey lines, the auto-generated grid region spacing lines being displayed in a lighter grey. The currently selected grid region is selected in cyan or yellow if the region is a non-default inserted region. To select regions on one of the other major axes, you can change the axis by clicking on the required axis of the axis selector displayed at the top right of the screen:

To edit a grid region, move the mouse cursor across the grid to the required region that will highlight to indicate that it has been selected and then click the mouse button. The selected region will then highlight in red and the ‘Edit CFD Grid’ data panel will be displayed at the bottom left of the screen:

The following settings are available on the Edit CFD Grid data panel:

Operation:

1–Edit Region - change the spacing of the currently selected region.
2–Insert Region- insert a new custom key coordinate at a defined point in the current region to form an additional region.
3–Remove Region - this option is only available if the current region has been previously inserted and allows you to remove it.

New coordinate (m)

If the ‘Insert Region’ operation has been selected, this setting is displayed allowing you to define a custom coordinate within the current region. Note that the coordinate must lie in the range defined by the displayed start and end coordinates.

Spacing Type

The spacing type can be set to one of the following:

1-None - the region is not sub-divided.

2-Uniform - the region is sub-divided into a number of equal sub-divisions, the dimension of which is calculated to be as close to the specified ‘Spacing dimension’ as possible.

3-Increasing power-law - the location of each sub-division grid line within the region increases as the power of the spacing number, which starts at the beginning of the region. So that if i represents the index number of the grid line counted from the start of the region, the coordinate of the i^th sub-division grid line is calculated using the following relationship: x_i=(region dimension)(i/n)^power+x_s

4-Decreasing power-law - the location of each sub-division grid line within the region decreases as the power of the spacing number, which starts at the end of the region. So that if i represents the index number of the grid line counted from the start of the region, the coordinate of the i^th sub-division grid line is calculated using the following relationship: x_i=(region dimension)[1-(i/n)^power]+x_s

5-Symmetric power-law - the coordinate of the i^th sub-division grid line is calculated using both increasing and decreasing power-law relationships that meet at the middle of the region:

For i <= n/2: x_i=[(region dimension)/2](2i/n)^power+x_s

For i >= n/2: x_i=[(region dimension)/2][2-(2i/n))^power]+x_s

Spacing dimension (m)

If the uniform spacing type has been selected, this setting is displayed and allows you to enter the dimension used for sub-dividing the region.

Spacing power

If the Increasing/Decreasing/Symmetric power law spacing type has been selected, this setting is displayed and allows you to enter the power used in the associated power-law spacing relationship.

Number of divisions

If the Increasing/Decreasing/Symmetric power law spacing type has been selected, this setting is displayed and allows you to enter the number of divisions used in the associated power-law spacing relationship.

After selecting an operation and adjusting the required settings, you then need to click on the ‘Apply changes’ button to update the selected grid region with the current settings.