Identification of Structural Stiffness and Damping Coefficients of a Shoed-Brush Seal

Abstract

The multiple-shoe brush seal, a variation of a standard brush seal, accommodates arcuate pads at the bristles’ free ends. This novel design allows reverse shaft rotation operation and reduces and even eliminates bristle wear, since the pads lift-off due to the generation of a hydrodynamic film during rotor spinning. This type of seal, able to work at both cold and high temperatures, not only restricts secondary leakage but also acts as an effective vibration damper. The dynamic operation of the shoed-brush seals, along with the validation of reliable predictive tools, relies on the appropriate estimation of the seal structural stiffness and energy dissipation features. Single-frequency external load tests conducted on a controlled motion test rig and without shaft rotation allow the identification (measurement) of the structural stiffness and equivalent damping of a 20-pad brush seal, 153mm in diameter. The seal energy dissipation mechanism, represented by a structural loss factor and a dry friction coefficient, characterizes the energy dissipated by the bristles and the dry friction interaction of the brush seal bristles rubbing against each other. The physical model used reproduces well the measured system motions, even for frequencies well above the identification range.