THEORETICAL VS EXPERIMENTAL ROTORDYNAMIC COEFFICIENTS OF INCOMPRESSIBLE-FLOW LABYRINTH SEALS

A detailed finite element-based perturbation analysis, initially developed for straight annular seals, is extended to the labyrinth seal rotordynamics problem. This particular seal category is frequently used in turbopumps, such as those of the Space Shuttle Main Engine, for its effectiveness as a leakage control device. The same seal configuration is also known to produce a net destabilizing force, which stems from the fluid/rotor interaction mechanism. The general objective here is to assess the effect of a design parameter, namely the number of tooth-to-tooth chambers, on the seal rotordynamic characteristics and relative stability. To this end, two representative cases of teeth-on-rotor labyrinth seals are selected for the purpose of comparison. The chosen seals share the same tooth-to-tooth chamber geometry, but are composed of one and five such chambers. The computed rotordynamic coefficients are compared to an existing set of experimental measurements concerning the same two seal configurations. The final outcome of the study is consistent with the general belief that labyrinth seals impart a rotordynamically destabilizing effect. In terms of relative stability, however, the rive-chamber seal configuration offers less of this destabilizing effect, by comparison.