Study of Forces and Dynamic Coefficients in Whirling and Eccentric Labyrinth Seals Using ANSYS-CFX

Labyrinth seal force estimates are important to the prediction of the stability of turbomachinery. The force prediction methods fall into several categories: experiments, bulk flow analysis, and finite volume analysis. Finite volume analysis can be split into two subcategories: self-developed and commercial. In this research, a commercial computational fluid dynamics (CFD) program called ANSYS-CFX was used to predict the forces generated in a labyrinth seal whirling at specified speeds. The results were compared to data from VT-FAST, a bulk flow code, and TASCflow, another commercial CFD program. It was shown that there were discrepancies among the results, and several hypotheses were made as to the reason for these discrepancies. Additionally, ANSYS-CFX was used to study the effect of labyrinth seal eccentricity ratio on the resultant force generated. It was shown that the radial force component within the seal behaved linearly with respect to eccentricity ratio. However, the tangential force component had no distinguishable relationship with the eccentricity ratio. It was hypothesized that the lack of a relationship was caused by the small fluctuations in the inlet swirl. Although the inlet swirl varied very little at each eccentricity ratio, it was shown there was a relationship between the tangential force and inlet swirl.