CFD Study on Stepped and Drum Balance Labyrinth Seal

Abstract

The stability of rotors in turbomachines is affected by the labyrinth seal where driving forces are generated. Recent research results have shown that the preswirl has a significant influence on the rotordynamic characteristics of the straight labyrinth seal including both tooth-on-stator and tooth-on-rotor configurations. However, modern turbomachines require higher and higher pressure drop for the seal so that the eye seal is usually designed as stepped labyrinth, whereas the balance drum usually employs a tooth-interlocking labyrinth and a larger number of teeth. Both designs could generate greater forces on the rotor than the straight labyrinth seal. Therefore, it is necessary to further study the influence of preswirl on stepped and tooth-interlocking labyrinth seals. This article employed 3D calculational fluid dynamics (CFD) to solve the flow in those seals. Then the rotordynamic coefficients of the two seals at different preswirl rates were calculated based on the CFD results. The results were compared with test data and bulk flow results. A rotor stability analysis was conducted considering the balance drum seal with the coefficients predicted by the numerical method.