Operating life assessment of a carbon fibre brush seal through endurance testing

Abstract

While brush seals have been studied for almost forty years, carbon fibre brush seals have only recently drawn interest for their excellent leakage performance, combined with low friction. Their suitability for oil sealing applications has been acknowledged in the aeronautical field, specifically for civil aircraft gas turbine engines. This paper focuses on the endurance of optimally designed brush seals in an environment simulating the bearing chamber working conditions. They underwent a wide range of differential pressures and rotational speeds in long runs ranging from 100 to 300 h. A semi-empirical performance prediction model was developed based on these results, allowing estimation of the leakage performance beyond the recorded data. In addition, the presence of lubrication oil largely increases seal life, despite initial leakage performance degradation due to hydrodynamic lift. Finally, a visual inspection with a high precision microscope revealed uprooting of the carbon fibres. This phenomenon may well be the biggest cause of performance degradation, rather than fibre material losses, which were ultimately deemed unquantifiable.