Comparison of the Leakage Characteristics of the Straight Annular and Convergent Seals

Annular seals are devices, which are used in turboMachinery systems to reduce the flow leakage, and to provide better dynamic stability to the system. Leakage flow can strongly affect cooling quality, heating balance, and efficiency of a turboMachinery system. Due to the fact that annular seals can significantly reduce the flow leakage, and provide the most cost-effective way of enhancing the aerodynamic efficiency, understanding of the flow characteristics through the annular seal configurations is an important subject.

Seals are classified in two main groups, which are contacting, and non-contacting seals. Straight annular and convergent seal configurations are characterized as non-contacting seals, and they are widely used in rotating turbocMachinery systems. The flow kinetic energy obtained from the flow pressure is dissipated by the effects of shear stresses along the free shear layers. In addition, viscosity of the flow has an impact on the dissipation rate of the flow kinetic energy.

In this research, the leakage characteristics of the straight annular, and convergent seal configurations under specified working conditions are compared to each other. This study aims to investigate which seal configuration exhibits better leakage characteristics with respect to the different seal clearances, shaft speeds, surface roughness heights, and pressure ratios.

Commercial code ANSYS Fluent is used to perform the flow simulations for the straight annular and convergent seal configurations. Effects of the seal clearances, shaft speeds, pressure ratios, and surface roughness heights on the leakage rate are analyzed. It was observed that the seal clearance has a significant impact on the flow leakage, and clearance control is an important subject in seal technology. Additionally, dynamic system is compared to the static system, and results showed that shaft speed less than 15,000 rpm has not considerable impacts on the leakage.