Define convection boundary conditions at 2D interfaces

Learn how to define thicknesses on 2D components and control thermal behavior at 2D interfaces. You will stitch interfaces, display free and stitched edges, apply thicknesses using expressions and specialized bolt/hole definitions, and validate areas used by the solver for convection and thermal couplings.

Download and extract the part files.

Introduction

Applying a mesh to a body is straightforward; however, defining thickness and controlling thermal behavior at 2D interfaces requires careful attention.

In this tutorial, you will:
  • Define thicknesses on various 2D components.
  • Stitch interfaces in the FEM.
  • Display and verify stitched edges.
  • Apply thickness using expressions, bolt definitions, and hole definitions.
  • Define Thermal Stream and Thermal Coupling boundary conditions.
  • Evaluate the impact on conductive and convective areas.
  • Verify the convective area used by the solver.

Define assembly load options

Load components from the same directory as the parent assembly.

  1. On the Home tab, click Assembly Load Options .
  2. From the Load list, select From Folder.
  3. Click OK.

Open the Simulation file

Open the simulation file and reset the dialog box settings.

  1. Choose File→Open and open thermal_bcs\HPC_sim.sim.
  2. Choose File→Preferences→User Interface and on the Dialog and Precision page, reset the dialog box memory.
  3. Click OK.

Display free and stitched edges

Open the workshop simulation and configure the display to review free edges and stitched edges.

  1. In the Simulation Navigator, right-click HPC_fem.fem and choose Open in Window.
  2. Choose Menu > Preferences > Model Display.
    Alternatively, right-click the FEM file and select Edit Model Display.
  3. Select Polygon Edges, then enable Display Free Edges and Display Stitched Edges.
    Free edges appear as pink lines. After stitching, internal edges appear as blue lines.

  4. Click OK.

Stitch edges at the airfoil and disk interface

Stitch edges together at the base of the airfoil. In this case, thermal couplings between the blade and disk are not required, and convection boundary conditions can be applied to one internal edge, instead of two free edges.

  1. Choose Home > Polygon Geometry > Stitch Edge .
  2. Make sure that Method set to Automatic.
  3. Select the polygon bodies of the disks and the blades at the airfoil and disk interface.


  4. Click OK.
    Notice that internal edges between the airfoils and disks are highlighted in blue.

  5. Choose Home > Context > Update to update meshes.

Apply thickness properties to the meshes

Apply thickness definitions to all plane stress regions and verify the results using thickness contours.

  1. In the Simulation Navigator, right-click 2D Collectors and choose Plot Thickness Contours.
    This helps identify meshes with zero thickness regions.

    Observe that four meshes have zero thickness and must be updated. Blade 1, blade 2, the bolt shank, and the bolt hole attached to disk 1.

  2. In the Simulation Navigator, expand the 2DCollector > Plane Stress Blades , right-click 2d_mesh(8) of the blade1 and choose Edit Mesh Associated Data.
    When using a single instance for a blade that represents all blades, convection area on faces often requires an explicit instance-based area factor later.
  3. From the Thickness Source, select Field/Expression to define bolt thickness properties.
  4. In the Thickness box, type 0.5*2*radius*pi() to define a radially varying thickness using an expression.
  5. In the Number of Instances box, set the blade to use 1 instance that represents all blades.
  6. Click OK.
  7. Right-click 2d_mesh(9) of the blade 2 and choose Edit Mesh Associated Data.
  8. From the Thickness Source, select Field/Expression.
  9. In the Thickness box, type 0.5*2*radius*pi()/50 to define the thickness expression for a single blade.
  10. In the Number of Instances box, set the number of instances to 50.
  11. Click OK.
  12. In the Simulation Navigator, expand the Plane Stress Bolts, right-click 2d_mesh(4) and choose Edit Mesh Associated Data to define the bolt shank mesh properties.
  13. From the Thickness Source, select Bolt to define bolt thickness properties and specify the bolt centerline.
    The centerline displays as a light blue line in the graphics window.
  14. In the Number of Instances box, set the number of instances to 45.
  15. Click OK.
  16. Inspect the mesh-associated data for the bolt head in 2d_mesh(5) as an example of an alternative method for defining the bolt centerline and for removing edges from the bolt thickness selection.
  17. In the Simulation Navigator, expand the Plane Stress Bolt Holes, right-click stage_1_blisk_bolt_hole and choose Edit Mesh Associated Data to edit mesh associated data for the bolt hole mesh.
  18. From the Thickness Source, select Hole to define hole thickness properties.
  19. In the Number of Instances box, set the number of instances to 45.
  20. Click OK.
  21. In the Simulation Navigator, right-click 2D Collectors and choose Plot Thickness Contours again to confirm thickness is defined for all plane stress regions..


Apply thermal streams

Apply one-sided and two-sided thermal streams on internal edges, faces, and free edges, and control the convection area used by the solver.

  1. Switch to the Simulation window to make the simulation active.
    When the simulation is active, the Simulation file is highlighted in blue.
  2. Choose Home > Load Type > Thermal Stream to apply a one-sided edge stream on the internal edge of blade 1.
  3. Make sure that Type is set to One-Sided Stream on Edges.
  4. In the Name box, type a meaningful name. For example, Blade1_root_ID1.
  5. Select the shown edge.


    Click Reverse Direction if the arrow orientation does not match the direction shown in the image.

  6. In the Fluid group, from the Fluid Materials, select Air.
  7. In the Stream Conditions group, set:
    • Mass Flow = 0.1 kg/s
    • Inlet Temperature = 200 °C
    • Absolute Pressure = 0.1 MPa
    • Area for Internal Edges = Subtract Thickness to subtract the blade thickness from the disk thickness to determine the convective area used for the stream.
    • Heat Transfer Coefficient = 100 W/(m2·°C)
    • Heat Pickup = 0
  8. Click Apply.
  9. Apply a one-sided face stream to the face of the blade 1 in the Z-direction as shown. Name the stream as Blade1_airfoil_ID2.
  10. Set the following:
    • Fluid Materials = Air
    • Mass Flow = 0.9 kg/s

      Notice the difference in mass flow applied to the face stream versus the edge stream. In 2D gas turbine flow path modeling, it is common to split the total mass flow into multiple streams so that part of the flow convects with the airfoil, while other portions convect with the disk and stationary components (not shown here). In this example, 90% of the mass flow is applied across the blade and 10% across the disk, ensuring the thermal capacity of the air is properly represented.

    • Inlet Temperature = sti(1) °C

      This allows the user to reuse the inlet temperature of another stream to better streamline the model setup and updating.

    • Absolute Pressure = sp(1) MPa
    • Area Correction = Factor
    • Area Correction Factor = 2*50

      The 2 represents the front and back sides of the blade, and the 50 represents the number of instances. The 50 is required since we set the mesh associated data to have a single instance.

    • Heat Transfer Coefficient = 100 W/(m2·°C)
    • Heat Pickup = 0
  11. Click Apply.
  12. Apply a one-sided edge stream on the internal edge of the blade 2 as shown. Name the stream as Blade2_root_ID3.


  13. Set the following:
    • Fluid Materials = Air
    • Mass Flow = smo(1) kg/s to reference massflow from the stream 1.
    • Inlet Temperature = mix(1,2) °C

      Use the mix() function to perform an enthalpy mix of previously created streams.

    • Absolute Pressure = sp(1) MPa to reference pressure from the stream1.
    • Heat Transfer Coefficient = 100 W/(m2·°C)
    • Heat Pickup = 0
  14. Click Apply.
  15. Apply a one-sided face stream to the face of the blade 2 in the Z-direction. Name the stream as Blade2_airfoil_ID4.


  16. Set the following:
    • Fluid Materials = Air
    • Mass Flow = smo(2) kg/s to reference massflow from the stream 4.
    • Inlet Temperature = sti(3) °C to reference inlet temperature from the stream 2.
    • Absolute Pressure = sp(3) MPa to reference pressure from the stream 2.
    • Area Correction = Factor
    • Area Correction Factor = 2//2 sides, number of instances is defined.

      The factor of 2 accounts for the front and back surfaces of the blade. The blade-count area scaling is handled by setting the number of instances to 50 in the mesh-associated data.

      Note the // in the Area Correction Factor field. Using // after populating a field in the dialog box allows you to add comments to boundary conditions, helping document area factors and thermal correlation inputs.

    • Heat Transfer Coefficient = 100 W/(m2·°C)
    • Heat Pickup = 0
  17. Click Apply.
  18. Apply a two-sided edge stream to model leakage flow passing between two components with free edges. Name the stream as Disk_2_3_leakage_ID5.
    Two-sided streams are used here because there are two free edges on the path. Conduction between the components is added later using a thermal contact.
  19. In the Simulation Navigator, under Polygon Geometry, hide the disk_2 and three ROTOR_STAGE_2_BOLT to ensure consistent edge selections for Side A.
  20. For the Side A:
    • Select the four shown edges of the flange from the disk 3.

    • Display the disk 2, and in the Path Limits group, select Define Start Point, from the list choose End Point and select the shown edge to ensure the stream begins where the two components interface.

  21. For the Side B:
    • Select four edges of disk 2 as shown.

      Hide the disk3 to ensure consistent edge selections for Side B.



    • Display the disk 3 and in the Path Limits group, select Define End Point, from the list choose End Point and select the shown edge to ensure the stream ends at the inner radius of the disk 3 flange.

  22. Set the following:
    • Fluid Materials = Air
    • Mass Flow = 0.001 kg/s
    • Inlet Temperature = sto(3) °C
    • Absolute Pressure = sp(3) MPa
    • Heat Transfer Coefficient = 100 W/(m2·°C)
    • Heat Pickup = 0
  23. Click OK.

Apply the thermal contact between the bolt head and disk 1

Create the thermal coupling in the bolt head to the disk1 region.

  1. Choose Home > Simulation Object Type > Thermal Coupling to define the contact between the bolt head and disk 1 region.
  2. In the Name box, type Bolthead_to_Disk1_TC.
  3. Show all polygon geometries.
  4. In the Top border bar, set the Type Filter to Polygon Edge.
  5. Display the three ROTOR_STAGE_2_BOLT components and select the smaller region, consisting of the three edges of the bolt head, as a primary region. For easier selection, hide the disk 1.


  6. Select three edges of the disk 1, as a secondary region.


    Tip: To focus on a specific polygon body during selection, expand the Body Focus group in the dialog box, click Select Body and select disk1 in the graphics window. Once selected, all other polygon bodies become temporarily translucent and unavailable for further selection.

  7. In the Magnitude group, from the Type list, select Heat Transfer Coefficient and set to 200 W/m2·°C.
  8. Click OK.

Verify solver-used areas

Validate the solver-used area when internal lines are present.

At the transition from bolt head to shank, an internal edge exists and is included in the thermal coupling as shown.

For regions like this, it is good practice to verify the area used by the thermal coupling to ensure accurate heat flow. Use the HPC_sim-Solution_1.bcdata file to identify the area calculated by the solver, then perform a hand calculation to confirm the correct contact area.

If you are using a version earlier than 2606, include the DISPLAY BC SUMMARY TABLES advanced parameter to write thermal and fluid properties of some boundary conditions in the file <simulation name>-<solution name>.bcdata.

The image on the right shows the actual thermal contact area that should be used. For the contact between the bolt head and the disk 1, the correct area is:

mm2

  1. In the Simulation Navigator, right-click the Solution 1 and select Solve to execute the solve.
  2. Open the HPC_sim-Solution_1.bcdata file and inspect the reported area for the thermal coupling.


    The convective area is calculated as 3343 [mm2].

    The area correction factor for the HTC is

    Since the solver-calculated area depends on mesh resolution and the correction factor is very close to 1, the area factor can be omitted for this thermal coupling.

Apply thermal contacts in the bolt head to disk 3, disk 1 to FHS, and disk 2 to disk 3

Create edge-to-edge contacts in the bolt head to disk 3, disk 1 to FHS, and disk 2 to disk 3.

  1. Choose Home > Simulation Object Type > Edge-to-Edge Contact to define the contact at the interface between the bolt head and disk 3.
  2. Select the Manual type.
  3. Name the contact as Bolthead_to_Disk3.
  4. For the Source Region, select the shown edge.


  5. For the Target Region, select the shown edge.


  6. In the Thermal Properties group, select the Activate Thermal Coupling check box.
    Edge-to-Edge Contact allows thermal and structural contact to be defined using a single simulation object for thermo-mechanical workflows.
  7. From the Type list, select Heat Transfer Coefficient, and set to 200 W/m2·°C.
  8. Click OK.
  9. Apply two additional thermal couplings using the process shown in the Apply the thermal contact between the bolt head and disk 1 with a Heat Transfer Coefficient of 500 W/m2·°C.
    Disk 1 to front hollow shaft (FHS) Disk 2 to disk 3

    Primary region is the edge of the Disk 1.



    Secondary region is the edge of the front hollow shaft.

    Primary region is the edge of the Disk 3.



    Secondary region is the edge of the Disk 2.
  10. Solve the model and inspect the .bcdata.


  11. Inspect the temperature contours. The following image shows the nodal temperature results at 5000s.


Additional notes

  • Use the PLOT BC SUMMARY TABLES advanced parameters to review areas used in streams and thermal couplings.
  • Pay special attention to convection areas on faces: solver-used area depends on mesh instance counts and any defined area factors or overrides.