Coupled problem

This exercise demonstrates creating meshes for coupled multi-domain problems where interface connectivity is critical.

Problem Description

Consider the cooling of a solid block by a fluid flowing through circular cross-section channels. The channel is centered within a square cross-section block. The outer boundaries of the solid are adiabatic.

Two domains need to be created:

• Domain 1: Solid block
• Domain 2: Fluid channel

Key requirement: Mesh elements must be connected at the interface between domains for TRUST to read the mesh correctly.

Setup

mkdir -p TRUST_TUTORIALS/salome/exo4
cd TRUST_TUTORIALS/salome/exo4
$PathToSALOME/salome &

• Create a new study: File → New
• Select the Geometry module
• Save frequently in HDF format

Creating the Geometry

• Create the solid block: New Entity → Primitives → Box
  • Dx = 200, Dy = 200, Dz = 400
  • Click "Apply and Close"
• Create a vertex for the cylinder base: New Entity → Basic → Point
  • X = 100, Y = 100, Z = 0
  • Click "Apply and Close"
• Create the fluid channel: New Entity → Primitives → Cylinder
  • Base Point: Vertex_1
  • Vector: OZ
  • Radius R = 40
  • Height H = 400
  • Click "Apply and Close"
• Cut the cylinder from the block: Operations → Boolean → Cut
  • Main Object: Box_1
  • Tool Objects: Cylinder_1
  • Click "Apply and Close"
• Create a partition: Operations → Partition
  • Objects: Select both Cylinder_1 and Cut_1
  • Click "Apply and Close"

Note: This partition ensures mesh connectivity at the interface.

Defining Volume Groups

Create groups for each domain:

• Solid domain: New Entity → Group → Create Group
  • Shape Type: Volume
  • Name: Solid
  • Main Shape: Partition_1
  • Select the hollow box
  • Click "Add" → "Apply"
• Fluid domain: Continue in the same dialog
  • Name: Fluid
  • Main Shape: Partition_1
  • Select the cylindrical channel
  • Click "Add" → "Apply and Close"

Defining Boundary Groups

Create surface groups for all boundaries:

• Fluid inlet: New Entity → Group → Create Group
  • Shape Type: Surface
  • Name: Fluid_inlet
  • Main Shape: Partition_1
  • Select the bottom of the cylinder → "Add" → "Apply"
• Fluid outlet:
  • Name: Fluid_outlet
  • Select the top circular boundary → "Add" → "Apply"
• Solid top:
  • Name: Solid_top
  • Select the top of the box → "Add" → "Apply"
• Solid bottom:
  • Name: Solid_bottom
  • Select the bottom of the box → "Add" → "Apply"
• Solid lateral walls:
  • Name: Solid_lateral_walls
  • Select the four lateral boundaries of the box → "Add" → "Apply"
• Solid-Fluid interface:
  • Name: Solid_Fluid_Interface
  • Select the top of the box → "Hide selected"
  • Select a lateral boundary → "Hide selected"
  • The lateral surface of the cylinder should now be visible
  • Select it → "Add" → "Apply and Close"

Creating the Mesh

• Switch to the Mesh module
• Create the mesh: Mesh → Create Mesh
  • Name: Mesh_1
  • Geometry: Partition_1
  • 3D algorithm: NETGEN 1D-2D-3D
• Configure parameters:
  • Click the wheel icon next to "Hypothesis" → "NETGEN 3D Parameters"
  • In "Arguments": Change fineness from "Moderate" to "Fine"
  • Click "OK" → "Apply and Close"
• Compute the mesh:
  • Right-click on "Mesh_1" → Compute
• Verify groups:
  • Check that six boundaries appear under "Group of Faces" of Mesh_1
  • Check that two volume groups appear under "Group of Volumes" of Mesh_1

Exporting the Mesh

• Export to MED format:
  • Select "Mesh_1"
  • Right Click → Export → MED file
  • Choose MED 3.2 if possible
  • Save as Mesh_1.med
• Dump the study: File → Dump Study
  • Save as a Python script (needed for the next exercise)

Running the Coupled Problem

Copy and run the TRUST data file:

cp $TRUST_ROOT/docs/exercices/salome/Coupled_pb.data .
trust Coupled_pb.data

Visualize the results with VisIt:

visit -o Coupled_pb.lata

Plot the temperature field on both domains and set the color bar min/max to 300 and 400 respectively. You will observe the solid cooling over time. Given sufficient simulation time, the solid temperature will eventually match the fluid temperature at steady state.