The calculation of rotordynamic coefficients for labyrinth seals

The effect of labyrinth seals on rotordynamic stability is well established. In order to account for forces resulting from nonuniform circumferential pressure distributions within a labyrinth seal, stiffness and damping coefficients are required for use in a rotordynamic analysis. In this thesis, a single control volume, bulk flow method (Iwatsubo based) for the calculation of these coefficients is developed and implemented in the form of a computer program. This program is based upon earlier work performed by the ROMAC Industrial Research Program at the University of Virginia. Significant modifications to the mass flow rate calculation and the formulation of the governing sets of equations are implemented in the present analysis. A parametric analysis of the effect of mass flow rate on rotordynamic coefficients is performed and suggests that a small variation between the calculated and experimental mass flow rates should not significantly detract from the accuracy of the dynamic coefficients and that the mass flow rate calculation implemented in this report is sufficiently accurate for use with the Iwatsubo method. The use of tangential momentum parameters proposed by Jenny and Kanki is shown to have little effect on the rotordynamic coefficients and does not lead to improved correlation with experimental data. Comparisons to experimental data suggest that the computer program based on this analysis is reasonable for use as a design tool to predict the trends and actual values of cross-coupled stiffness, the most important seal parameter in rotordynamic analyses. The program is also shown to be useful in predicting the order of magnitude of principal stiffness and damping coefficients