Brush Seal Bristle Wear Analysis

Abstract

Turbomachinery sealing applications require accommodating large rotor excursions at high surface speeds. Achieving seal compliance under such demanding conditions combined with typical high operating temperatures poses a major engineering challenge. Formed by a dense pack of bristles, brush seals have emerged as viable alternatives to conventional labyrinth seals. Being contact seals, brush seals undergo unavoidable bristle wear in operation. Rate and extent of bristle wear determines seal life and performance. Detailed understanding of brush seal contact loads is necessary to estimate seal 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 summary of a 3-D computational brush seal tip force and wear analysis. The analysis models 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 calculate resulting seal stiffness and tip forces. Results are compared to stiffness measurements and full scale seal wear tests.