Systematic Numerical Investigation on the Surface Roughness Effects on the Friction and Heat Transfer of Additively Manufactured Components

Abstract The gas turbine community is increasingly exploring additive manufacturing (AM) for cooling applications, aiming to consolidate parts, enable higher system complexity, as well as boost performance without raising costs or lead times. However, AM introduces challenges, such as geometrical deviations and surface roughness, especially for tiny features, high scan speeds, and small building orientations. These defects can significantly increase the pressure drop and more marginally the heat transfer. Over the past decade, many studies have experimentally analyzed the thermo-hydraulic performance of cooling features such as straight and wavy channels, pin fins, ribs, and more recently, lattice and triply periodic minimal surface (TPMS) structures. Less attention is devoted to the numerical simulations accounting for such roughness effects, which are typically neglected by considering smooth walls and as-designed ideal geometries. The objective of the present work is to provide calibration guidelines for roughness modelling and identify the conditions for which roughness plays a significant role and needs to be accounted for or, on the other hand, where its effects can be conservatively disregarded in the design process. Considering this, a CFD roughness model was calibrated against experimental data across several test cases including circular, rectangular, and wavy minichannels, as well as Kagome and body-centered cubic lattice structures. Additionally, the impact of roughness on the thermo-hydraulic performance of these structures was evaluated by scaling the geometries for different hydraulic diameters. The results showed distinct trends for each geometry, highlighting different levels of sensitivity to roughness as the hydraulic diameter of the channels is changed.