DSMC-SANDIA Interface

The DSMC-SANDIA interface writes an input file from an ICEM CFD/CAE surface grid and its attached boundary conditions in the format read by the DSMC-SANDIA solver.

The translator writes the SANDIA input file using the
structured domain file(s) from PADAMM (domain.1 to domain.n), the
index files from PADAMM (index1 to index*n*), the boundary
condition file from MULCAD (boco), and the topology file from
MULCAD (topo_mulcad_out). To create the input file, select the
translator "DSMC-Sandia" in the "Output" menu
from the ICEM CFD/CAE Manager. After clicking "Write
output" you can specify options for the interface:

- give the name of the boundary condition file

(default is*configuration*/parts_mesh/mesh/boco) - give the name of the topology file

(default is*configuration*/topology/topo_mulcad_out) - give the name of the SANDIA-DSMC input file

(default is*configuration*/parts_mesh/transfer/*configuration*)

The interface generates the input file located in the Transfer Shell. You may open a shell window in this directory by selecting the menu items "Utility" and "Transfer Shell".

The boundary conditions are defined using the "Unspecified Bound. Cond." menu in MULCAD. In this menu the user can specify the boundary conditions on each edge of the model. Please refer to the General Remarks section for more details.

**Boundary Type Code:**

The available boundary type codes for sides 1 through 4 are:

- 1: Line of symmetry
- 3: Free stream bound. cond. (constant values)
- 3
*x*: Free stream bound. cond. (variable values using subroutine bc).

*x*indicates appropriate table entry to use from subroutine bc.

If*3x>0*, use*x*in table. Else use*y*, radial source line. - 4: Free stream bound. cond. (reflective-subsonic) single pump
- 5: Solid surface
- 5
*x*: - 7: Connection to another region
- 8: Outflow (non-reentrant)
- 9: Porous wall (extra bc in input)
- 10: Outgassing surface

The boundary type code must be specify under *NR* in the
boundary condition menu. If a type 5, 5*x* or 10 is chosen,
additional boundary conditions can be specified. These correspond
to the entries in the BC table of the DSMC-SANDIA input file: *Spec.
refl., Temp. K, Material #,* and *Value*. Finally, the
maximum cell weight needs also to be defined in this menu, under
the entry *SCALE*(7). A default value of 300 is given for
the maximum cell weight. This value can be changed here while
setting the boundary conditions.

MULCAD Default ------ ------- 2.NREnter the boundary type code (see table above) 3.VALUEIf applicable, enterSpec. Refl.0.0 4.XIf applicalbe, enterTemp. K273.0 5.YIf applicable, enterMaterial #0 6.ZIf applicable, enterValue0.0 7.SCALEEnter the maximum cell weight 300

A serie of rules must be carefully followed when constructing the model in MULCAD:

- Only 2D models -single or multiblock- are supported by the interface.
- Each region must be composed of 4 edges. These edges can be shared with other regions as long as the edge meshing is the same for both regions. For adjacent regions with different edge meshing, edges can not be shared. This means that for a model composed of 5 regions, the MULCAD model would have 20 edges.
- Each edge must be composed of only 1 segment.
- The normal of all subfaces must point toward the z+ axis.
- The x-axis is assumed to be oriented from the left to the right and the y-axis from the bottom to the top. The order of the global points are calculated accordingly.
- The sides are grouped by pair: the lower and upper sides forming pair 1-3 and the left and right sides forming pair 2-4. A pair of sides can be either linear or circular. That is, if side 1 is an arc, side 3 must also be an arc.
- The sides can make an angle with the x-y axis. However, they must not exceed a 45 deg. angle deviation. For example, side 1 which is along the x-axis can form a max angle of 44.9 deg. with the axis. Above that, the definition of the lower/upper left/right corners does not hold anymore.
- A boundary condition must be defined for each side except for interface edges where a boundary type 7 is given by default.

N.B. The actual version expects a maximum of six adjacent regions per side.