Aerodynamic Characterization of LPBF Manufactured Honeycomb Like Sealing Designs Within a Labyrinth Sealing

Laser Powder Bed Fusion (LPBF) is an enabling technology to manufacture complex and thin-walled geometries. Former publications have successfully proven the application of the LPBF pulse wave approach to produce additive manufactured (AM) sealing segments, meeting the general geometrical requirement of 0.1 mm wall thickness. The objective of this paper is the continuative characterization of LPBF sealing structures regarding their aerodynamic behavior. An analytic optimization, based on the geometric leakage coefficient with a new approach of calculation, is chosen to define the optimal cell design for small clearance. Four different LPBF designs including hexagon and rhombus shapes are accompanied by a conventional honeycomb and a smooth liner for comparison. In order to characterize the leakage behaviors all samples are tested at a pre-established test rig of the KIT (Karlsruhe Institure of Technology). The experimental test plan includes the variation of the gap distance between 0.2 and 1.2 mm and an equal increase of the pressure ratio (PR) from 1.1 to 2.0. The performance is determined by measuring the mass flow rate and static pressure conditions within the chambers of a labyrinth sealing plate by means of nine pressure tubes. The results indicate a higher sealing efficiency for AM design at low sealing gaps. An increase of the gap distance to 1.2 mm favors the conventional honeycomb. The expected grading of the sealing performance according to the geometric increase factor could not be demonstrated. The consideration of the discharge coefficient (CD) shows the qualitative application of the new effective gap distance. For three liner structures the discharge coefficient appear to be constant at varying sealing gaps. The higher sealing performance of two LPBF designs in comparison to the standard honeycombs at small gap widths shows the potential for future investigations.