Infrared Thermography-Based Heat Transfer Analysis and Thermal Boundary Layer Evaluation on Upscaled Models of Additively Manufactured Rough Surfaces

Additive Manufacturing (AM), and in particular Laser Powder Bed Fusion (L-PBF), enables the fabrication of complex internal geometries that are not feasible with traditional manufacturing techniques such as casting or milling. This capability is especially beneficial for gas turbine components, where advanced cooling channel designs are required to sustain high thermal loads and improve overall engine efficiency. However, a direct consequence of the AM process is the formation of unique surface roughness (SR) patterns, which affect both pressure loss and convective heat transfer (HT) mechanisms. In particular, AM-induced SR tends to be irregular and highly stochastic in nature, deviating from traditional roughness characterizations based on sand grain analogs. To better understand the effect of such SR on local heat transfer behavior, a dedicated experimental rig—the Surface-Roughness-Heat-Transfer (SRHT) rig—was developed at the Fluid Dynamics Laboratory of Siemens Energy AB. The rig enables the study of convective heat transfer on upscaled physical models of AM surfaces using infrared (IR) thermography, with air as the working fluid. Upscaled geometries are modeled from real AM surfaces using scanning electron microscopy and surface topography data, allowing detailed spatial evaluation of the local heat transfer coefficient (HTC). In this study, the SRHT rig was extended to promote fully developed channel flow conditions and improved thermal diagnostics. With the upgraded facility, existing upscaled Aluminium and Inconel test objects were retested to re-evaluate previously obtained heat transfer data. A comprehensive repeatability analysis was conducted by varying the infrared camera positions to verify the robustness and spatial consistency of the HTC measurements. Additionally, this work introduces—for the first time within the project—a systematic investigation of the thermal boundary layer development along the flow direction over AM-induced surface roughness. Boundary layer profiles were obtained through distributed surface temperature measurements and analyzed in conjunction with spatial HTC maps. This dual approach allowed deeper insight into the interplay between local flow behavior and convective heat transfer augmentation due to roughness features. The results confirm the combined influence of increased effective surface area and roughness-induced turbulence on the heat transfer enhancement observed on AM surfaces. This study consolidates the infrared thermography methodology, validates the robustness of the experimental process, and extends the project's scope by integrating thermal boundary layer analysis into the heat transfer characterization framework.