CFD and experimental investigation of AM surfaces with different build orientations

Additive manufacturing (AM) surfaces offer the possibility of novel cooling channel geometries for high temperature applications. AM processes can optimize the internal geometry of cooling channels, which is generally constrained by limitations of conventional machining processes. The AM process gives rise to surface textures that depend on the build and scan orientations that also potentially contribute to heat-transfer characteristics and provide additional considerations for optimization. The motivation behind this research work is to explore the correlation between AM roughness characteristics (build-orientations, density of spatter deposits and their sizes, amplitudes/wavelengths, etc) and the resulting effect on heat transfer and pressure drop across cooling channels. In this study, the actual AM surfaces with different build angles were fabricated using Laser powder bed fusion (LPBF) and the roughness data of these surfaces were acquired. These measured surface topographies were used for developing simplified surfaces for the purposes of CFD simulations. Modeled AM surfaces with different build orientations were used to analyze the effect of built orientation and spatter deposits in terms of heat transfer for different flow conditions. The CFD simulations also informed the design of the experimental set-up for the validation of computational results. For the comparison, a reference smooth surface is machined from forged Inconel-625 for experiments and CFD simulations were also carried out for the validation. Results from CFD simulations show that the surface features (such as build angles and spatter deposits) significantly affect the heat transfer and fluid flow in terms of Nusselt number and pressure drop and the surface area impact on heat transfer is minimal in all the cases for both laminar and turbulent flow conditions. Under turbulent flow conditions, transverse track alignment shows the highest efficiency in terms of the Nusselt number and adding particles improves heat transfer efficiency for smooth and parallel-tracked surfaces. However, when the flow becomes laminar, reversed behavior is observed and surfaces show downside effects in terms of Nu. Also we define a performance factor that assesses the combined effects of both the thermal and the fluid flow characteristics to differentiate the performance of the AM channels.