There are two menus concerning the boundaries:

  1. The Locate Boundaries menu: it is used to create the boundaries (i.e. to associate the cell faces with a boundary). In this menu the type of boundary can be set.
  2. The Define Boundaries menu is the place where the boundaries attributes are set (like the speed for an inlet for example)



    Selecting cells faces for Boundaries

The first step is to create the boundaries with the locate Boundaries menu or with appropriate commands.

Each new boundary must be associated to a region number to be selected in the menu. Yet a boundary can be composed of for example two non connected walls as long as their properties are identical. If boundaries regions have not been explicitly declared by the user they will be automatically be considered as walls.

It is important to know that you can add new boundaries (cell faces) to a boundary region anytime. For example you can pick 2 cell faces and confirm the creation of 2 boundaries and then select more faces that will be added to the already created boundaries. This feature is useful when can't select all the faces at once. To unselect some cells faces you must delete the boundary region or use the boundary toolbar.

The particularity of the attach boundary type is described here.


There is 4 ways to select cell faces as boundaries in the the Locate Boundaries menu:

  1. Pick cell faces: It is the easiest way. Using the cursor the cells faces can be selected one by one by clicking on them.
  2. Select a zone: also an easy way. By clicking on the graphical window the user defines a zone that encircles the faces to be selected. Warning: the faces must be visible to be selected.
  3. Surface based on edges: by clicking a vertex all cell faces of the same type are selected until an edge is reached. It is a fast way to select large zones, but it doesn't work when the vertex is on an edge (when the face as a width of one cell).
  4. Surface based on Vset: works the same as Surface based on edges.
When selecting graphically cells it is most of the time necessary to do several selections. It is then useful to plot the already selected cells using the B>New>... menu.

    Using Commands

Additionally boundaries can be defined by using the BDEFINE and BGENERATE commands: BDEF set the boundary region and a starting face. BGEN is used then two select further faces by setting the index change. It can therefore only be used when the vertex numbering is regular. To use this command it is important to find the cell with the lowest vertexes for the BDEF command as the index will than increase. To do this turn the vertex numbering on: in the graphical window Plot>Number>Vertex.

BDEFINE, NREGION(1), NV1, NV2, NV3, NV4, NPATCH: Defines a boundary for a cell face
NREGION   Region number to which this boundary is referenced.
NV1, &, NV4   Four vertices defining a cell face.
NPATCH   Radiation patch number to assign. Boundaries must have a patch number if they are on radiation cells.

BGENERATE, NREP, NVINC, NB1(1), NB2(NB1), NBINC(1):  Generates NREP sets incrementing all vertices by NVINC. The initial set is included in the NREP count. NB1, NB2, NBINC   Initial set of boundaries defined by NB1 to NB2 by NBINC.

For example:

to define the boundary region 5 composed of 3 faces:

BDEF 5 10 11 31 30
!! This command select the first face (defined by the vertexes 10 10 31 30. Warning: the order is important 10 11 30 31 won't work (twisted face)!) of the boundary region 5 (the first number).

BGEN 3 1 30 30 1
!!This commands defines a boundary composed of 3 cells (the first argument), the vertex number of the face is incremented by 1, the boundaries that will be taken as model are the boundaries number 30 to 30 in this case, the boundaries will be numbered by starting at number 30, the boundary index is incremented by one at each new boundary (creating boundaries 30 31 32 is this case).

Checking the selected cells for Boundaries

The boundary toolbar

The boundary toolbar is used to manage the boundaries. With this toolbar you can view all existing boundaries, delete a boundary, compress the boundaries numbering....

Boundary list

Use the Boundary list to check if you have the right number of boundaries. If it is not the case it is possible that some case have been selected twice looking at the vertex indexes. You can delete all the useless boundaries (you can use Shift or Crtl to select an array of boundaries).


When you have deleted boundaries the boundaries numbering has "holes". To have a regular numbering again use this button.

The plotting of boundaries
To look at the selected cells, go to the Locate Boundaries menu and use the Plot region boundary or Plot all boundaries to display them in the graphical window.

To go back to the grid view unselect the BOUN button in the graphical window an turn the edges on by clicking on the little white cube.

It can be useful to select or unselect the plotting of a particular boundary; In the graphical window use B>New>... to plot a specific type of boundaries. To avoid the plotting of a boundary use B>delete>... (it will not delete the boundary)


As the mesh was generated with Star-CD the numbering is regular and BDEF and BGEN can be used.

To view only the inside mesh use
and click on an inside mesh cell
Plot cells

Turn the Vertex numbering on

Find the inside wall cell face with the lowest vertex index:
it shoud be
this face will be your starting point.
BDEF 1 1615 1616 2023 2022

Generate the other boundaries
BGEN 36 1 1 1 1

Go to Locate Boundaries
Select region 1 and Plot Region.


As for the cylinder wall: display only the inside cells and find the minimum vertexes on the outside.

then type:

BDEF 2 1985 1986 2393 2392
BGEN 36 1 37 37 1


For the outside cells display only the outside mesh.
Go to the Locate Boundaries menu
Select region 3
Select type cyclic to have a better view

Use Pick cells faces to select the inside faces
You must select the faces in the same order as for the other attach: start with the face opposite to the one used in BDEF and turn in the same direction.
You will not be able to select all faces at once.

So select 10 faces then use
Plot Boundary region
Turn Edges On

Pick other faces by respecting the order.
Use B>New>Cyclic
Replot to see all the selected faces
and continue until all cells are selected.

Then Plot all boundaries

Verify in Boundary tools> Boundary list the number of boundaries (108 at this time)


For the inlet and outlet you must use the Locate Boundaries menu.

In the graphic window set the view to be able to see the cells that will form the Inlet.

In the menu select 6 on the list and set the type to Inlet.
Pick cells faces
Click on the faces to be selected.

Then start again with the region 7 for the Pressure.

(You can also use the select a zone method)


Set the view back to Default.

Go to the Locate Boundaries menu.
Select region 5, select type Symplane
Use Surface based on Edges.
Click on a vertex off the outside mesh
Use Surface based on VSET.
Click on a vertex of the inside mesh.
Use View>Axis>-Z to flip the view
Use Surface based on VSET.
Click on a vertex off the outside mesh
Use Surface based on VSET.
Click on a vertex of the inside mesh.


Go to the Define Boundaries menu.

Select region 1
Coord sys.: 4
Omega: 300

Select region 2
Coord sys.: 4

Region 3 is like region 2

Select region 6
Coord sys. 1
U: 1 (or appropriate speed setting)


When generating the inside mesh the first and last Vertex are at the same position and must now be merged.

It is better to do this after the boundaries to keep the vertex numbering

Create a new Coordinate system 5 with the setting in the Create and Import Grids > Create Grids > Create 3D Grids menu:
Cartesian, Xc=0,5, Yc=0,5.
Set it active

Click on the inside mesh
VSET NEWS GRAN 0.049  0.251 -0.001, 0.001,,, 5
Then go to Create and Import Grids > Assemble Grid >Vextex Merge tab
Select High as the KEEP option
Click Merge.