Simplified Improvement of Higher Order Extended Bulk Flow Analysis Specialized for Derivation of Rotordynamic Coefficients of the Annular Plain Seal With Large Static Eccentricity

Rotordynamic (RD) fluid force of turbomachinery is known as one of the causes of the shaft vibration problem. Bulk flow analysis is the analytical method of RD fluid force, and it is widely used in design stage. Conventional bulk flow analysis has been basically carried out under the assumption of concentric circular whirl orbit. While, the actual turbomachinery is often operated with static eccentricity due to the effect of static load and so on. However, there are not many studies that have investigated the case with large static eccentricity, in particular, the case more than half the seal clearance. In this paper, the linear RD coefficient for the plain annular seal is focused on and examined for the range that static eccentricity is up to 65% of seal clearance. In this range of static eccentricity, it requires the nonlinear analysis extended to the fifth order and largely increases the number of equations to be solved. This paper proposed simplification of higher order extended bulk flow (SHEBF) analysis, and as a result, the number of analytical equations to be solved is significantly reduced. The validity of this method is confirmed both numerically and experimentally.