3-D ANALYSIS OF A HIGH DENSITY BRUSH WITH FRICTIONAL CONTACT INTERACTIONS

The physical complexity of dense brush structures presents major challenges to analyzers. As they maintain their flexibility at elevated temperatures, which are typical in gas turbines, high density brush seals made of super-alloy bristles found popularity among engine designers. Typically brush-rotor contact occurs at very high surface speeds. If not managed properly, this may result in extreme wear conditions and damage to rotor. In order to ensure engine operational safety brush contact loads should be controlled through seal design and detail analysis. In addition to the physical complexity of these dense brush structures, frictional contacts among the bristles themselves, between the bristles and the support plates, and between the bristles tips and the high speed rotor further increase the analysis complexity, and make it a major undertaking if not impossible. Detailed understanding of brush seal contact loads is necessary to estimate seal and rotor wear performance. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study details that may not be available through analytical formulations. This work presents a 3-D computational brush seal structural FE model that can be used to calculate bristle stress, tip force, and do wear analysis. The analysis includes a representative brush segment with bristles formed by 3-D beam elements. Bristle interlocking and frictional interactions (interbristle, bristle-backing plate and bristle-rotor) are included to better simulate pressure-stiffness coupling. Various analysis results are presented and compared to full scale seal wear tests.