Experimental validation of optimised straight-through labyrinth seals with various land structures

Seals in turbomachinery have a huge impact on efficiency. The labyrinth seal a with honeycomb land is one of the most popular solutions applied in gas turbines to control secondary flows. The presented paper shows experimental validation of labyrinth seal optimisation, working with various innovative honeycomb-type lands. The analysis focuses on the straight-through seal configuration with two fins. Such a configuration is expected in regions with limited space, common in modern jet engines. Four configurations of the straight-through labyrinth seal are presented: with a smooth land, a honeycomb land, a squeezed honeycomb and a rhomboid land. The labyrinth reference geometry and the optimised ones are investigated experimentally. The CFD-based optimisation results presented in the previous work revealed a significant reduction in leakage, up to 24%. The study described in this paper validates the numerical computations and confirms the potential for improvement of labyrinth seals. The tests were performed on an air-fed test stand, with the pressure ratio loading range of 1.05-1.8, which is representative of the aero-engine interstage seals. The leakage amount, the total inlet parameters and the pressure distribution in the sealing specimen were all monitored using high-frequency transducers in real time. The schlieren technique was applied for flow visualisation. Satisfactory agreement is found between the results of the CFD simulations and the experimental data. All the trends and tendencies observed in the CFD study are confirmed proving the robustness of the proposed optimisation methodology. However, in some cases, certain discrepancies between the CFD-optimisation results and the test data can be noticed. The experimental and the numerical schlieren images are presented, which enables a comparison of flow patterns in particular seal configurations. The study indicates that it is possible to design the sealing in a manner that makes it possible to keep leakage relatively stable in a wide range of operating parameters different clearances and pressure ratios. (C) 2020 Elsevier Ltd. All rights reserved.