Labyrinth Seal Rotordynamic Characteristics Part I: Operational Conditions Effects

Abstract

The objective of this work was to determine the effects of the operational conditions (as shown in this paper) and geometric parameters [as shown in Part 2 (LiZ.LiJ.FengZ., “Labyrinth Seal Rotordynamic Characteristics Part II: Geometrical Parameter Effects,” Journal of Propulsion and Power, Vol. XXX, No. XXX, 2016, pp. XXX–XXX)] on the leakage and rotordynamic characteristics of labyrinth seals. In this paper, the effects of the operational conditions, such as the pressure ratio, rotational speed, and inlet preswirl, were numerically investigated. A novel transient computational-fluid-dynamics method based on the multifrequency elliptical whirling orbit model was used to predict transient leakage flow rates and frequency-dependent rotordynamic coefficients for a tooth-on-stator, labyrinth gas seal. The accuracy and availability of the transient computational-fluid-dynamics method were demonstrated with the experimental data of frequency-dependent rotordynamic coefficients at two rotational speeds with inlet preswirl. Transient computational-fluid-dynamics solutions were conducted at three pressure ratios (three inlet pressures and three outlet pressures), three rotational speeds, and three inlet preswirl ratios. Numerical results of leakage flow rates and rotordynamic coefficients for different operational conditions were presented and compared, paying special attention to the effective stiffness, effective damping, and crossover frequency of the effective damping term. The conclusions show that the magnitudes of all seal force coefficients are roughly proportional to the seal supply pressure but insensitive to the backpressure. Increasing rotational speed and increasing inlet preswirl both result in a significant decrease in the effective damping as well as an obvious increase in the crossover frequency and destabilizing cross-coupling stiffness.