Model radiation on 3D components

Model radiative heat transfer on 3D components and compare full radiation solution with the simplified approach and evaluate solve time trade-offs.

Download and extract the part files.

Introduction

Radiative heat transfer can significantly influence component temperatures in gas turbine engines, particularly where convection is weak or components with large temperature differences have a direct line of sight.

Radiation is typically important in regions such as:

  • The exhaust assembly, where hot diffuser walls radiate to cooler outer casings
  • The turbine inlet, where components are exposed to combustion gases

When deciding how to model radiation, consider:

  • Can you represent components with 2D elements?
  • Can you apply cyclic symmetry?
  • Can you divide the model into multiple enclosures to reduce solve time?
  • Can you accept reduced accuracy to achieve significantly faster solve times?

This tutorial compares two radiation modeling approaches:

  • Full enclosure radiation with periodic radiation enabled.
  • Simplified radiation using thermal couplings and precomputed gray-body view factors.

Load and inspect the model

Inspect components, identify radiating regions, and review boundary conditions.

  1. Choose File→Open and open radiation/strut_sim1.sim.
  2. Inspect the geometry and identify the major components of the 1/5 sector cyclically symmetric model.


  3. Determine which components will radiate to each other.
    The most significant radiative exchange occurs between the strut shield and the strut, where both the temperature difference and view factor are large. Significant radiation also occurs between the diffuser and the casing because of their large facing surface areas.
  4. Inspect the temperature constraints applied to:
    • The outer casing
    • The inner casing
    • The diffuser
    • The strut shield
  5. Select the temperature constraints, right-click the selection, and select Plot Contour to visualize the applied temperatures.


Explore the radiation enclosure

Explore the defined radiation enclosure that uses the Monte Carlo view factor calculation method.

In this analysis, you can choose from several modeling approaches. For example, you could divide the radiation enclosure into three separate regions, as shown, to reduce solve time.
  1. Activate the Radiation solution.
  2. Under the Simulation Object node, right-click Radiation_other and select Edit to explore it.
    Use this approach when you need to compute view factors only once, extract them, and reuse them in subsequent analyses.
  3. Notice that:
    • The enclosure includes the inside casing surfaces, outside diffuser surfaces, the strut, and the inside of the strut shield.

      34 surfaces are included.

    • The Monte Carlo method is selected.
    • Number of Rays is set to 2000.

      You can increase the ray count if required until the results converge to the required accuracy.

    • The Include Radiative Environment option is cleared.
  4. Click OK.
    This enclosure provides the most accurate radiation solution because all participating surfaces can exchange radiation within a single enclosure, allowing the solver to account for all visibility and shadowing effects.

    To reduce solve time, the model could instead be divided into multiple radiation enclosures.



    However, this approximation prevents surfaces in different enclosures from exchanging radiation. For example, surfaces in enclosure 1 may physically see surfaces in enclosures 2 and 3, but these interactions are ignored. As a result, the solver performs fewer visibility and shadowing calculations, reducing computational cost but decreasing solution accuracy.

Explore Cyclic Symmetry

Explore periodic radiation in a cyclic symmetry model.

  1. Under the Simulation Object node, right-click Cyclic Symmetry and select Edit to explore it.
  2. Notice that:
    • Source and target regions define the cyclic faces.
      Source Region Target Region




    • The Dynamic coordinate system is selected.
    • The number of calculated segments is 5.
    • Two solid bodies are assigned to Stage 1.
    • Enable Radiative Thermal Rotational Periodicity is selected.

      When this option is enabled, the solver replicates the model around the complete annulus and computes radiation exchange between all cyclic sectors.

    Although this produces the most realistic solution, it substantially increases the time required to compute view factors.

    Common methods for reducing solve time include:

    • Using the GPU Computed View Factors method.
    • Subdividing solid bodies and applying swept meshes to reduce the number of surface elements.
    • Reducing the number of heat flow reports, as they require additional iterations.
    • Running the thermal solver in parallel.
    • Using radiation patches. You can define them either in Advanced Parameters or in the solver options under Radiation. Note that these methods behave differently.

    This tutorial intentionally uses the full configuration to generate accurate view factors that will later be reused in a simplified model.

Explore Heat Map reports

Explore the Heat Map reports applied to several regions of interest for view factor calculations.

  1. Under the heat_maps folder, inspect the created reports.
    These reports define groups used to calculate heat flow and view factors between important regions.
    Name Selection
    outer_case

    outer_diff

    outer_strut

    inner_case

    inner_diff

    inner_strut

    strut_shield

    mid_strut

  2. Edit the Advanced Controls simulation object, and notice that the VIEW FACTOR TABLE advanced parameter is defined to output the view factors table for heat maps.

Inspect the view factor results

A full radiation enclosure solution requires hours to solve. Instead, use the supplied results.

  1. Navigate to the solution directory, open strut_sim1-Radiation_View_factors.csv, and review the computed view factors.
  2. Use only the dominant gray-body view factors listed below when creating the Thermal Coupling – Radiation simulation object in the simplified model.
    From To Black Body View Factor (ij) Gray Body View Factor (ij) ScriptF(ij)
    Outer
    outer_case outer_diff 8.385794e-03 3.3517566 2.6814077
    outer_case outer_strut 4.099724e-02 0.43345985 0.3467682
    outer_diff outer_strut 1.126600e-02 0.22132197 0.17705737
    Middle
    strut_shield mid_strut 6.164241e-01 2.2735267 1.8188225
    Inner
    inner_case inner_diff 1.433695e-01 3.5060833 2.8048646
    inner_case inner_strut 2.308919e-02 0.51408845 0.41127047
    inner_diff inner_strut 6.411320e-01 0.84458834 0.67567039

    For the simplified model:

    • Use the Gray Body View Factor because it accounts for diffuse reflections.
    • Divide each view factor by the number of cyclic sectors.

Build the simplified radiation model

Replace the enclosure radiation with gray-body radiation thermal couplings.

  1. Activate the Radiation_Simplify solution.
  2. Choose Home > Loads and Conditions > Simulation Object Type > Thermal Coupling - Radiation to represent radiative exchange.
  3. In the Primary Region group, select the shown faces.
  4. In the Secondary Region group, select the shown faces.
  5. From the Type list, select Gray Body View Factor.
  6. In the Gray Body View Factor box, type 3.352/5.
  7. Clear the Only Connect Overlapping Elements check box to couple the entire primary region to the nearest secondary region.
  8. Create six additional radiation couplings using the dominant gray-body view factors.
    Primary Region Secondary Region Gray Body View Factor
    0.433/5
    0.221/5
    2.274/5




    		3.506/5




    		0.514/5




    		0.845/5
    Note:
    The emissivity of the mesh collector is used in the radiation calculation along with the grey body view factor to calculate radiative heat flow.
  9. Edit the Cyclic Symmetry and notice that the Enable Radiative Thermal Rotational Periodicity check box is cleared.
    This option only affects Radiation Enclosure calculations. Since the simplified model uses radiation thermal couplings instead of an enclosure, this setting has no effect.
  10. Solve the Radiation_Simplify solution.

Create Result Probes

Create a Result Probe to calculate the average nodal temperature of the strut region most affected by radiation.

  1. Choose Results > Manipulation > Result Probe to extract the averaged nodal temperature of the strut region most affected by radiation.
  2. Set the following:
    • Formula = temp_nodal
    • Load Case = All
    • Iteration Selection = All
    • Selection Type = Nodes
    • Select the strut region which is most affected by radiation.

    • Select the Combine Across Entities check box.
    • Combined Value = Average
    • Unit = °C
    • Output Options = List
    • Clear the Create Output check box
  3. Create a graph.

Compare results

Create and overlay graphs for two solutions.

In the Post Processing Navigator, with one of the graphs already displayed, press CTRL and select the second graph, then choose Overlay.

From these curves, the following conclusions are:

  • The simplified radiation model predicts an average temperature within approximately 6 °C of the full radiation model at steady-state conditions.
  • The close agreement between the full radiation model and the simplified model validates the use of gray body view factors and radiative conductances in the simplified approach.

Additional Notes

  • Avoid excessive heat map reports to reduce solve time.
  • Review solve times for two solutions.