Experimental Characterization of Variable Bristle Diameter Brush Seal Leakage, Stiffness and Wear

Brush seals are used in a wide variety of turbomachinery for sealing rotor-stator and stator-stator clearances. Application of traditional brush seals is limited by their life and performance at high differential pressures. GE’s patent-pending Variable Bristle Diameter (VBD) brush seal overcomes the limitations of the traditional brush seal by sandwiching a layer of fine bristles, with better sealing capability, between adjacent rows of stiffer bristles capable of withstanding larger differential pressure and flow disturbance. The General Electric VBD design uses thick bristles both in front and back rows. In addition to leakage performance, for successful design it is important to understand the force interactions between a brush seal bristle pack and the rotor. The important failure mechanisms to avoid include overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness, defined as brush seal force per unit circumferential length per unit incursion of the rotor, depends on the complex interaction of the pressure-dependent inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack. Furthermore, brush seals exhibit different hysteresis and wear behavior under different pressure loading conditions. In this article, we present experimentally measured leakage, stiffness and wear characteristics of three different VBD brush seal designs subjected to a wide range of pressure loading.