Tae Woong Ha* and Bok Seong Choe
The Journal of Mechanical Science and Technology, vol. 26, no. 4, pp.1043-1048, 2012

Abstract : Annular seals are primarily used to control the leakage in turbomachinery, such as pumps. Consequently, annular seals substantially affect the stability of turbomachinery. Designing the annular seals of high performance pumps require the accurate prediction of the seal’s leakage flow rate and rotordynamic coefficients. The bulk-flow model is the traditional means for leakage flow rate analysis and predictions. Bulk-flow analysis is based on the Hirs’ lubrication equation, which simplifies the Navier-Stokes equation. However, the analysis of the bulk-flow model requires a great amount of time to develop an analysis code. Furthermore, the code possesses many constraints for analyzing seals with complicated shapes. 3D CFD simulations provide faster and less expensive estimates of the flow field for a wide variety of operating parameters and flow conditions. In this study, the flow field and the rotordynamic coefficients of a plain-eccentricannular seal were simulated with circular whirl orbits using 3D CFD code. A relative coordinate system was defined to calculate the 3D velocity profile and the dynamic pressure distribution of the seal clearance for each rotor whirling speed. The rotordynamic coefficients were determined by reaction forces of seal fluid, which were calculated by integrating the dynamic pressures to the whole area of seal. The results from our analyses were compared to existing theoretical calculations as well as compared to results acquired from experiments. The present 3D CFD results of leakage and rotordynamic coefficients of K and C showed better improvement in prediction.

Keyword : Bulk-flow model; CFD; Centrifugal pump; Eccentric-annular seal; Rotordynamic coefficients