Porous Jump Boundary Condition

Porous Jump Boundary Condition#

The Porous Jump boundary condition models a thin, permeable membrane (e.g. a filter, screen, or heat exchanger core) as a surface interface that introduces a pressure drop proportional to the local flow velocity.

Available Options#

Option

Description

Applicable

Name

Identifier for this boundary condition

always

Darcy coefficients

Viscous (linear) resistance coefficient of the porous layer

always

Forchheimer coefficient

Inertial (quadratic) resistance coefficient of the porous layer

always

Thickness

Physical thickness of the porous layer

always

Assigned surfaces

Matching pairs of interface surfaces that define the porous jump

always

Detailed Descriptions#

Name#

A user-defined label to identify this boundary condition within the simulation.

  • Default: PorousJump

  • Example: "heat_exchanger_core", "filter_screen"

Darcy coefficients#

Scales the viscous (linear) pressure-drop term across the porous interface.

  • Units: 1/m²

  • Required.

  • Example: 1e6 / fl.u.m**2

Forchheimer coefficient#

Scales the inertial (quadratic) pressure-drop term across the porous interface.

  • Units: 1/m

  • Required.

  • Example: 1.0 / fl.u.m

Thickness#

The physical thickness of the porous layer represented by the surface interface.

  • Units: m

  • Required.

  • Example: 0.05 * fl.u.m

Note: The thickness does not need to match the actual mesh geometry — the surface is treated as an infinitely thin interface in the mesh, and the thickness is used only inside the pressure-drop model.

Assigned surfaces#

Matching pairs of interface surfaces on either side of the porous layer.

  • Required. Each entry is a pair: (upstream face, downstream face).

  • Accepted types: Pairs of interface Surface objects.

  • Example: blk-1/Interface-blk-2 paired with blk-2/Interface-blk-1

Note: Both surfaces in each pair must be interface boundaries between two adjacent mesh blocks. This boundary condition is only available when the simulation is set up starting from a volume mesh.

💡 Tips

  • Mesh Requirements

    • Interface surfaces: The porous jump surfaces must be internal interface boundaries between adjacent mesh blocks. Conformal (node-matching) meshes are recommended for best accuracy.

  • Coefficient Estimation

    • Darcy and Forchheimer coefficients can be derived from experimental pressure-drop vs. velocity data by fitting: Δp/t = μ · D · v + ½ · ρ · F · v²

    • Alternatively, they can be obtained from the manufacturer’s specifications for standard filter or heat-exchanger products.

🐍 Python Example Usage

 
import flow360 as fl

# Example: single porous interface (e.g. a heat exchanger core)
porous_jump = fl.PorousJump(
    name="heat_exchanger_core",
    surface_pairs=[
        (volume_mesh["blk-1/Interface-blk-2"], volume_mesh["blk-2/Interface-blk-1"])
    ],
    darcy_coefficient=1e6 / fl.u.m**2,
    forchheimer_coefficient=10.0 / fl.u.m,
    thickness=0.05 * fl.u.m,
)

# Example: multiple interface pairs sharing the same porous properties
multi_pair_porous_jump = fl.PorousJump(
    name="filter_screen",
    surface_pairs=[
        (volume_mesh["blk-1/Interface-blk-2"], volume_mesh["blk-2/Interface-blk-1"]),
        (volume_mesh["blk-1/Interface-blk-3"], volume_mesh["blk-3/Interface-blk-1"]),
    ],
    darcy_coefficient=1e6 / fl.u.m**2,
    forchheimer_coefficient=1.0 / fl.u.m,
    thickness=0.1 * fl.u.m,
)
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