Experimental evaluation of pocket damper seals with brush seal elements

Abstract

The brush hybrid pocket damper seal (BHS) has been proposed to replace a labyrinth seal or pocket damper seal (PDS) in a turbomachine when damping is desired without increased leakage. The BHS and brush-only seal are evaluated experimentally in both rotating and non-rotating tests. The primary objective is to determine if the BHS leaks less than a PDS while retaining or improving the PDS damping characteristics. Additionally, since the brush seals contact the shah, the effect of wear is investigated by testing journals of two different diameters. The rotating tests showed that the BHS and brush-only seal are potentially destabilizing through dry fiction whip. Methods of alleviating this instability are shown experimentally and analytically. Other tested characteristics include leakage, starting torque and dynamic coefficients. The worn BHS leaks half as much as a PDS at all test pressures. The starting torque of a brush seal increases strongly with pressure, however, the power dissipated at 6,000 R.P.M. never exceeds 1.5 horsepower. The dynamic coefficients, especially stiffness, also increase with increasing inlet pressure. Design recommendations are made for the successful implementation of a BHS to increase damping without increasing leakage.