Abstract
The literature already contains some experimental, analytical and numerical investigations on the rubbing and hysteresis behaviour of brush seals. What the investigations have in common is that they were carried out with new and uncontaminated seals, or that such a condition was assumed. The influence of contamination has not been explicitly investigated yet. Particularly in stationary gas and steam turbines, foreign substances can accumulate on and in the bristle package during steady-state operation. In the case of a rubbing event with a contaminated brush seal, e.g., during shutdown of the machine, the process is not expected to be comparable to that assumed in the presence of a new, uncontaminated seal. The present paper is dedicated to the question of the influence of contamination on the total frictional power loss generated during rubbing and the distribution of heat fluxes in friction contact. For this purpose, rub tests with two seals were carried out on the brush seal test rig of the Institute of Thermal Turbomachinery (ITS) in new conditions. Subsequently, the sealing packages were contaminated with oil or a salt mixture. After the treatment, the rub tests were repeated and compared with the previous tests. In addition, stiffness measurements were used to assess the degree of contamination. A strong influence on the rubbing behaviour by the contamination was detected. Contamination causes the flexibility of the bristle package to be greatly reduced. As a result, especially at the beginning of the first measurements, the total power losses and rotor heat inputs are strongly increased. This flexibility is partly regained in the course of the measurements. As expected, contamination also influences the hysteresis behaviour of the seal. A highly increased leakage rate after rubbing could be observed, because the bristles remained close to their deflected positions. In the case of the salted seal, however, an improvement in the leakage performance could be observed after several repeat tests.
Highlights
Brush seals have been applied in turbomachinery for over 30 years and have become a real alternative to labyrinth seals
The heat flux distribution is obtained as the ratio of rotor heat input calculated by means of the finite element analysis and the measured total frictional power loss: rotor heat input heat f lux distribution =
In order to ensure comparability of the results, the values were normalized to the starting value of seal 2 at 0.1 mm. Both the total power loss and the rotor heat input decrease with continuous testing. This can be explained on the one hand by progressive seal and rotor wear and on the other hand by a presumably deteriorated hysteresis behaviour of the seal due to contamination
Summary
Brush seals have been applied in turbomachinery for over 30 years and have become a real alternative to labyrinth seals. This type of seal is intended for use in almost every new aircraft engine and is mounted in land-based turbomachinery or retrofitted in existing plants. The research and development of brush seals began with rig tests, mostly at a component level, focusing on the leakage and wear properties of the seal. A large amount of information has been gathered on the long-term behaviour of brush seals as part of maintenance work and regular checks on the condition of the seals. The focus in assessing the seals was primarily on the wear condition and the change in leakage rates over time
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More From: International Journal of Turbomachinery, Propulsion and Power
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