Effects of Mushroom-Shaped Tooth Wear on the Leakage Performance and Rotordynamic Coefficients of Labyrinth Seals

Abstract

The leakage performance and rotordynamic coefficients of the labyrinth seal are changed when a mushroom-shaped tooth wear occurs in actual transient operation resulting from rubbing and wear between stator teeth and the rotor. The objective of current study was to numerically investigate and characterize the variation of the leakage performance and rotordynamic coefficients as a result of an increased mushroom-shaped tooth wear at two typical inlet preswirl velocities and enhance the rotor stability of the after-damage labyrinth seal. In this paper, the Unsteady Reynolds-Averaged Navier-Stokes (URANS) solution based on the multi-frequency elliptical orbit rotor whirling mode and dynamic mesh technique was used to calculate the leakage flow rates and rotordynamic coefficients of the labyrinth seal with an unworn clearance and three after-damage clearances at two inlet preswirl velocities. The accuracy and availability of adopted transient computational methods in this work were validated by the published experimental data. Also, the influence of tooth mushroom radius and each cavity in the labyrinth seal on the rotor stability and some approaches to improve the rotor stability were discussed and conducted. The conclusion shows that the leakage flow rate increases with an increase in the clearance, and a linear increase is expected when the after-damage clearance is over 0.4 mm. An increase in the after-damage clearance always leads to a drop in the effective damping or an increase in crossover frequencies. Also, the additional tooth mushroom radius plays an important role in the effective damping or crossover frequency and can not be neglected. The upstream cavity always possesses lower crossover frequency, and a drop of 9.9 Hz in the crossover frequency is found when the seal entrance axially extends 5 mm. In addition, the crossover frequency is decreased from 243.5 Hz to 164.2 Hz when typical anti-swirl brakes are installed in this labyrinth seal with the worn mushroom-shaped teeth.