Temperature, Heat-Flux & Convection Mapping from CFD to FEA

Thermal Mapping Is Not One Problem

CFD can provide several different thermal quantities: fluid temperature, wall temperature, heat flux, heat-transfer coefficient and reference/bulk temperature. These quantities play different roles in a thermal or structural model. A wall-temperature field can be mapped as a prescribed state, while a heat flux is an applied boundary flux; a heat-transfer coefficient requires a compatible sink or recovery temperature; a fluid-cell temperature is not automatically the correct wall boundary condition. Define what physical quantity is being transferred before selecting a mapping method.

Temperature Mapping to Structural FEA

When the structural model requires a temperature field for thermal strain and temperature-dependent properties, the mapped temperature should represent the solid temperature at the relevant time or steady condition. In conjugate heat-transfer analysis, this may come directly from the solid side of the CHT model. In a fluid-only CFD model, wall temperature may have been prescribed rather than predicted; mapping it back into FEA does not create new thermal evidence. Record the provenance of the temperature field and distinguish imposed from predicted quantities.

Heat Flux Mapping

Heat flux is an energy rate per area and must be integrated consistently over the target surface. Conservative mapping should preserve total heat rate as well as local distribution where thermal gradients matter. If source and target areas differ because of geometric simplification, a pointwise flux transfer can change total heat input. Compare integrated heat rate by region and explain any intentional difference.

Q_dot_source = ∫_A q″ dA
Q_dot_target = Σ_e ∫_Ae q″_mapped dA

For a conservative thermal transfer, Q_dot_target should match Q_dot_source within the project-defined tolerance.

Heat-Transfer Coefficient and Reference Temperature

A convection boundary condition usually requires both heat-transfer coefficient h and an associated fluid or recovery temperature T_ref. Mapping h alone is incomplete because heat flow depends on h(T_ref − T_wall). The pair may be correlated, particularly in compressible or separated flow, so independently smoothing them can distort local heat input. Where possible, verify the reconstructed heat flux against the CFD source after applying the pair to representative wall temperatures.

Interface Resistance and Contact Physics

The temperature predicted at a CFD wall does not include every thermal resistance that may exist in the structural assembly. Coatings, bond lines, thermal interface materials, contact pressure and internal conduction can create additional drops. The receiving thermal model should represent those resistances explicitly rather than forcing the CFD wall temperature onto an internal structural surface. The mapping boundary should be placed at a physically consistent interface.

Spatial Gradients and Thermal Stress

For structural assessment, preserving temperature gradient can be more important than preserving average temperature. Through-thickness gradients drive bending; local hot spots drive differential expansion and material-property reduction; circumferential gradients can ovalise shells or distort seals. Compare source and mapped gradients along structurally meaningful paths. A globally correct mean temperature can still produce the wrong stress if the gradient has been smeared.

Transient Thermal Transfer

For transient CFD/CHT, time alignment matters. If thermal boundary fields are transferred at discrete CFD output times, choose structural/thermal interpolation that preserves the important heating and cooling time scales. Do not independently interpolate strongly coupled h and T_ref fields without checking the resulting heat flux. Verify energy over the full transient as well as selected instantaneous states, especially when peak thermal stress occurs during a gradient transient rather than at maximum temperature.

Mapping Temperature onto a Different Structural Mesh

Nodal temperature mapping should avoid artificial discontinuities across material interfaces and should respect whether the structural elements represent a midsurface, layered shell or 3D solid. A single surface temperature mapped onto a shell cannot represent through-thickness gradient unless the shell formulation supports top/bottom temperatures or the gradient is reconstructed from a thermal solution. Be explicit about what through-thickness information is retained or lost.

Verification Evidence

Thermal transfer verification should include integrated heat rate where flux/HTC is mapped, min/max and area-average temperatures, representative spatial profiles, energy balance for transients, and a check that the structural thermal strain corresponds to the mapped temperature definition. Where thermal stress is critical, perform a sensitivity to plausible mapping smoothing or interface resistance.

Sequential Versus Iterative Thermal Coupling

A one-way thermal transfer is appropriate when structural deformation and solid temperature do not materially change the fluid boundary condition. If thermal expansion alters a gap, contact pressure, leakage path or cooling flow, the fluid and structural states may need iteration. The same applies when temperature-dependent solid conduction changes wall temperature enough to alter convection materially. State why one-way coupling is adequate, or define the convergence variables for an iterative loop such as wall temperature, heat rate, gap size or coolant flow. The mapping strategy should match the actual coupling strength.

Temperature-Dependent Material and Reference-State Consistency

The receiving structural model may use temperature-dependent modulus, yield data, thermal expansion and creep properties. Verify that the mapped temperature units and reference temperature are consistent with those material definitions. Thermal strain depends on the stress-free reference state, not merely the absolute peak temperature. A numerically accurate temperature map can therefore produce incorrect stress if the assembly or stress-free temperature is wrong. Include the structural reference state in the thermal-transfer review.

Thermal Mapping Through Global–Local Models

A system-level CFD or CHT model may supply boundary conditions to a detailed local thermal/structural model rather than map directly to the final stress mesh. Preserve both energy and the physically important gradient through this hierarchy. For example, a global model may define regional convection while a local model resolves a flange, seal or thin wall. Check that the local model does not unintentionally duplicate heat paths already represented globally, and confirm that local boundary truncation reproduces the parent temperature or heat-flow state away from the detail.

Thermal Result Interpretation

After the mapped thermal field is solved, compare not only peak temperature but also distortion pattern, restrained expansion force and stress sign with simple physical expectations. A wrong thermal reference state or swapped hot/cold region can still produce a converged solution. Check representative free-expansion estimates and support reactions to confirm that the mapped field is generating the expected structural mechanism.

Key Takeaway

Temperature, heat flux and convection data are different physical quantities. Transfer the correct quantity at the correct physical interface, preserve heat flow and gradients where relevant, and verify the thermal state before using it to generate structural stress.

Key takeaways

• Temperature, heat flux and convection data are different physical quantities.