
Porous jump conditions are used to model a thin "membrane'' that has known velocity (pressuredrop) characteristics. It is essentially a 1D simplification of the porous media model available for cell zones. Examples of uses for the porous jump condition include modeling pressure drops through screens and filters, and modeling radiators when you are not concerned with heat transfer. This simpler model should be used whenever possible (instead of the full porous media model) because it is more robust and yields better convergence.
The thin porous medium has a finite thickness over which the pressure change is defined as a combination of Darcy's Law and an additional inertial loss term:
where is the laminar fluid viscosity, is the permeability of the medium, is the pressurejump coefficient, is the velocity normal to the porous face, and is the thickness of the medium. Appropriate values for and can be calculated using the techniques described in Section 7.2.3.
User Inputs for the Porous Jump Model
Once the porous jump zone has been identified (in the Boundary Conditions task page), you will set all modeling inputs for the porous jump in the Porous Jump dialog box (Figure 7.3.37), which is opened from the Boundary Conditions task page (as described in Section 7.1.4).
The inputs required for the porous jump model are as follows:
Identifying the Porous Jump Zone
Since the porous jump model is a 1D simplification of the porous media model, the porousjump zone must be modeled as the interface between cells, rather than a cell zone. Thus the porousjump zone is a type of internal face zone (where the faces are line segments in 2D or triangles/quadrilaterals in 3D). If the porousjump zone is not identified as such by default when you read in the mesh (i.e., if it is identified as another type of internal face zone), you can use the Boundary Conditions task page to change the appropriate face zone to a porousjump zone.
Define Boundary Conditions...
The procedure for changing a zone's type is described in Section 7.1.3. Once the zone has been changed to a porous jump, you can open the Porous Jump task page (as described in Section 7.1.4) and specify the porous jump parameters listed above.
Defining Discrete Phase Boundary Conditions for the Porous Jump
If you are modeling a discrete phase of particles, you can set the fate of particle trajectories at the porous jump. See Section 23.4 for details.
Postprocessing for the Porous Jump
Postprocessing suggestions for a problem that includes a porous jump are the same as for porous media problems. See Section 7.2.3.