Numerical Investigations of Leakage Performance Degradations in Labyrinth and Flexible Seals Due to Wear

Abstract

The finite element analysis (FEA) and computational fluid dynamics (CFD) methods are utilized to investigate the leakage performance degradations in two kinds of flexible seals (i.e., forward bending and backward bending) and two kinds of shroud labyrinth seals (i.e., with straight fins and chamfered fins) in rubbing events. With the existing experimental data, FEA methods for contacting simulations and CFD methods for leakage rate and flow pattern predictions are carefully examined. The wear characteristic and leakage performance between labyrinth seals and flexible seals are compared before and after rub. The results show that, in rubbing process, the labyrinth seal with straight (symmetrical) fins is likely to undergo the mushrooming damage, whereas the labyrinth seal with chamfered (asymmetrical) fins is likely to undergo the tooth-bending damage. In rubbing process, compared with the labyrinth seal, the flexible seal has a superior characteristic in resisting the wear damage due to increased flexibility of fin. For a labyrinth seal with 0.3 mm design clearance and a flexible seal with 0.15 mm design clearance, the 0.5 mm radial displacement of rotor will result in 110% increase of leakage rate for labyrinth seal, and 7% increase of leakage rate for flexible seal after wear. Under the same conditions, the forward bending flexible seal has a lower leakage rate than the backward bending flexible seal before and after rub.