Perturbed Flow Structure in an Annular Seal Due to Synchronous Whirl

Abstract

This paper provides a thorough examination of the flow field resulting from synchronous whirl of an eccentric rotor in an annular seal under typical operating conditions. A new finite-element-based perturbation model is employed in the analysis, whereby perturbations in the flow thermophysical properties are attributed to virtual distortions in the rotor-to-housing finite element assembly. The numerical results are compared to a recent set of experimental data for a hydraulic seal with typical geometrical configurations and a synchronously whirling rotor. Despite the common perception that perturbation analyses are categorically confined to small rotor eccentricities, good agreement between the computed flow field and the experimental data is obtained for an eccentricity/clearance ratio of 50 percent. The agreement between the two sets of data is notably better at axial locations where the real-rig flow admission losses have diminished, and up to the seal discharge station. This attests to the accuracy of this untraditional and highly versatile perturbation model in predicting the rotordynamic characteristics of this and a wide variety of conceptually similar fluid/rotor interaction problems.