Elliptical Shape Hole-Pattern Seals Performance Evaluation Using Design of Experiments Technique1

Abstract

Hole-pattern annular gas seals have two distinct flow regions: an annular jet-flow region between the rotor and stator, and cylindrical indentions in the stator that serve as cavities where flow recirculation occurs. As the working fluid enters the cavities and recirculates, its kinetic energy is reduced, resulting in a reduction of leakage flow rate through the seal. The geometry of the cylindrical cavities has a significant effect on the overall performance of the seal. In this study, the effects of elliptical shape hole pattern geometry on the leakage and dynamic response performance of an industry-relevant hole-pattern seal design are investigated using a combination of computational fluid dynamics (CFD), hybrid bulk flow-CFD analysis, and design of experiments (DOEs) technique. The design space was defined by varying the values of five geometrical characteristics: the major and minor radius of hole, the angle between the major axis and the axis of the seal, the spacing between holes along the seal axis, and hole spacing in the circumferential direction. This detailed analysis allowed for a greater understanding of the interaction effects from varying all of these design parameters together as opposed to studying them one variable at a time. Response maps generated from the calculated results demonstrate the effects of each design parameter on seal leakage as well as the co-dependence between the design parameters. The data from this analysis were also used to generate linear regression models that demonstrate how these parameters affect the leakage rate and the dynamic coefficients, including the effective damping.