Flow Through Scaled Additive Manufacturing Internal Passages With Correlated and Anti-Correlated Roughness on Opposing Walls

Components created using additive manufacturing (AM) processes such as laser powder bed fusion (L-PBF) may exhibit a type of printing error referred to as a “layer shift error.” In this type of error, the reference location of the printing pattern shifts for each layer of material deposited. If an AM-printed component includes an internal cooling passage, the features or roughness of one wall of the passage may become anticorrelated to the roughness on the opposing wall of the passage. In this study, a rough surface from the internal passage of a L-PBF coupon was used to create two base surfaces representing flow through: (1) a passage oriented orthogonally to the printing direction and (2) a passage oriented at 45-deg to the printing direction. Each base roughness pattern was then shifted in the streamwise direction to produce either the nearest minimum correlation or the nearest maximum correlation and applied to the opposing side of the internal passage. Bulk friction factor measurements and particle-tracking velocimetry measurements of the flow were obtained for each minimum and maximum roughness correlation condition. The particle tracking results indicate that the flow shows the expected differences in flow patterns between the correlated surface conditions for the orthogonal surface. The resulting friction factors indicated statistically significant differences in the measured bulk friction between the opposing surface correlation conditions; however, the overall results suggest that correlation of roughness on opposing walls is not a significant design consideration regarding frictional losses for AM internal cooling passages.