Labyrinth seals are used to seal and regulate the mass flow between rotating components. Due to their non-contact functionality and thermal resistance, they are state of the art in sealing technology of thermal turbomachinery, such as aircraft engines or stationary gas turbines. Because of thermally and mechanically induced expansions during operation and transient flight manoeuvres, a contact, the so-called rubbing process, between rotor and stator cannot be excluded. To provide low leakages of the seal, the nominal clearance between the components is designed as small as possible. This increases the risk of a possible contact. In order to avoid structural damage of vital parts during rubbing, the material of rotor and stator must be selected with care. In addition, liners made from hollow body structures are applied to the stator. Honeycomb liners manufactured of bended and welded sheet metal are state of the art. The ultimate goal in seal design is an optimum sealing efficiency combined with a material behaviour of rotor and stator which provides low heat generation during rubbing and in case of wear preferably deterioration of the stator material. To obtain an efficient and reliable seal design the correlations between component loads and rubbing conditions must be investigated thoroughly and understood in detail. This paper will provide a vital experimental contribution to this objective.

A large amount of data concerning the rubbing process obtained from numerical and experimental investigations is available in public literature as well as at the Institute of Thermal Turbomachinery (ITS). The investigations were carried out for different velocity parameters, material combinations and component geometries. In addition with the experiments presented in this paper the effects of the different variables on the load due to rubbing are compared and discussed with focus on the material combination.  
Therefore the study is divided into three parts. First, possible materials for rotor and stator will be compared concerning their behaviour under mechanical and thermal load. In a next step, the extensive experimental work with the corresponding materials is presented. The experiments are carried out based on a simplified stator geometry at an existing versatile test rig at the ITS. A single Hastelloy X sheet represents the honeycomb stator. The rotor is made from Udimet 720Li, a superalloy with high temperature resistance. The sheet thickness (0.4mm and 0.5mm), the rubbing velocity (55m/s, 110m/s and 165m/s), the incursion rate (0.024mm/s, 0.25mm/s and 0,5mm/s) and the rubbing duration are varied. Contact temperatures and forces are measured with at a high-frequency sampling rate up to 100 kS/s. Abrasive wear is determined globally by means of weight loss of the metal foil.

The presented data could be compared with equivalent tests made with steel and other materials common in jet engines which have already been carried out at the ITS. The influence of the material on the loads can therefore be identified in such detail as never achieved before. One result was for example higher contact forces in the current experiments, due to a higher temperature resistance of the modulus of elasticity. The analysis will further be based on the rubbing of blade tips. A transferability of the data analysis to the rubbing process of blade tips is investigated.

Finally, design guidelines for labyrinth seals with optimum properties regarding toleration of rub events are derived. Based on the obtained knowledge a tool for designing reliable labyrinth seals for future engines will be available.


Experimental Investigation on the Rubbing Process of Labyrinth Seals Considering the Material Combination

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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