Three-Dimensional Computations of Rotordynamic Force Distributions in a Labyrinth Seal

Abstract

A numerical method employing a finite volume approach for calculating the rotordynamic force on eccentric, whirling labyrinth seals has been presented. The SIMPLER algorithm is used to calculate the three-dimensional flowfield within a seal. The modified bipolar coordinate system used accurately describes the geometry of an eccentric seal. The turbulent flow form of the fully elliptic Navier-Stokes equations was solved. A three-percent eccentric, single labyrinth cavity rotating at 7000 cpm was investigated for three different inlet swirl conditions, each with and without a whirl orbit frequency of 3500 cpm. It was found that the circumferential pressure variation around the downstream tooth periphery is by far the most important contribution to both rotordynamic force components. Thus the flowfield details near each tooth throttling should be carefully considered. Further, a substantial increase of shaft whirl frequency was found to decrease and increase the effect of cavity inlet swirl on F_t and F_r , respectively.

KEYWORDS:

• Rotordynamic Seal Forces
• Labyrinth Seals