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 that will certainly affect seal stiffness. 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. In addition to sealing performance, for successful design it is important to understand seal stiffness, the force interactions between a brush seal bristle pack and the rotor. Seal stiffness may affect bristle wear rate and cause non-uniform rotor heating that may lead to rotordynamic instability. Furthermore, VBD brush seals exhibit different hysteresis and wear behavior under different pressure loading conditions. In this article, we present design, manufacturing process and testing of the VBD design brush seals.
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