Contamination of Brush Seals by Oil and Salt and Its Impact on Rubbing and Hysteresis Behaviour

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.

Analysis of Heat Flux Distribution during Brush Seal Rubbing Using CFD with Porous Media Approach

“…The work by Pfefferle [13] was continued at the ITS in the subsequent years on a modified test rig (see Refs. [17][18][19][20]). The experimental investigations that were presented in these publications with subsequent calculation of the rotor heat input using an FE model demonstrated the influence of the geometry and operating parameters, as well as the degree of contamination of the bristle package on the heat flux distribution.…”

“…The recalculation of the experimental tests by means of the FE analyses (see Refs. [17][18][19]) has shown that the areas further inwards are only slightly thermally affected within the rubbing period of 30 s. At the inlet, the total pressure and temperature are set according to the respective measured values from the experiments. At the outlets, the static pressures and temperatures are specified.…”

Effect of the Fence Height on the Leakage Flow Characteristics of Brush Seals

“…Li et al (2012) analyzed effect of clearance sizes on the leakage performance of a labyrinthbrush seal and found that the blow-down effect should be considered for clearance brush seals. Hildebrandt et al (2019) experimentally investigated the effect of bristle pack density, rotor-bristle interference, rotational speed and pressure difference on leakage flow of a kind of clamped brush seal with an axially inclined bristles pack.…”