Non-Destructive Assessment of the Functional Diameter and Hydrodynamic Roughness of Additively Manufactured Channels

Metal additive manufacturing, particularly laser powder bed fusion, is increasingly used in the gas turbine industry for the fabrication of channels with small diameters for conformal cooling and flow passage applications. A critical challenge in this context lies in evaluating aspects such as the geometrical and hydraulic diameters, the effective area and the roughness on the internal surface of the channel that affects the flow functionality. This paper proposes a new method to evaluate the geometrical and functional equivalent diameters, i.e., the hydraulic diameter of cylindrical channels and the mean surface topography height on the internal channel surface, using X-ray computed tomography. The developed methods were validated with experimental flow tests, considering the mean surface topography height to be equivalent to the hydrodynamic sand grain roughness, thereby determining the hydraulic diameter and the associated effective area. The method is a much faster approach to determining the available hydraulic diameter compared to flow tests and offers the possibility of evaluating the internal surface characteristics, with discrepancies between the two approaches being less than ±3%.