Investigation of Annular Gas Seal Performance With Combined Cavity Patterns Using Computational Fluid Dynamics

Abstract

Abstract Annular gas seals are crucial components in turbomachinery applications since they reduce leakage flow from high-pressure to low-pressure sections. However, the fluid-induced rotor instabilities that may be governed by these components result in reduced efficiency and even failure in rotating machines. Thus, the proper selection and design of annular seals are critical to ensuring the stability and reliability of rotating machinery. Minimization of leakage rate while improving rotordynamic performance can be achieved by using proper cavity geometries. In this aspect, this work investigates leakage and rotordynamic characteristics of combined hole-pattern annular gas seals composed of circular and hexagonal patterns using 3D computational fluid dynamics (CFD). In literature, annular gas seals with circular and hexagonal cavities are investigated depending on shape of the patterns. According to previous research, the rotordynamic and leakage performance can be improved with the parameterization-based design optimization of the cavity shapes such as hole depth, diameter, distancing etc. Most of the existing studies investigate the performance of annular gas seals using bulk-flow analysis. Although bulk-flow model is more efficient in terms of computation time, CFD is a more proper tool to analyze patterned seals which have geometric complexity in terms of accuracy. The main reason is that the 3D CFD model enables to perform more realistic assumptions which results in more accurate outputs especially for complex designs in comparison to bulk-flow analysis. The performance of proposed combined-pattern seals is investigated comparing with the performance of existing industrial regular circular and hexagonal (i.e., honeycomb) patterned annular gas seals. Computational models are verified through existing experimental data for the circular hole-pattern seal which is selected as the baseline model. This investigation performs optimal selection of combined-pattern cavity geometry selected from the pool of configurations considered and provides an insight for further optimization efforts on patterned annular gas seals.