Modeling of the Divergently Worn Annular Seal for the Two-Way Coupled Fluid–Structure Interaction Analysis of Shaft Vibration and Clearance Flow

One of the causes of shaft vibration in turbomachinery is the rotordynamic (RD) fluid force. RD fluid force has a significant impact on the stability of the system, so it is necessary to carry out shaft vibration analysis considering the influence of RD fluid force at the design stage. The common methods for considering the effect of RD fluid force in shaft vibration analysis are linear RD coefficients and two-way coupled analysis. In the previous research, two-way coupled analysis was validated by experiment. However, Onset Speed of Instability (OSI) changed as experiment was repeated due to wear of seal stator. In order to explain this change, two-way coupled analysis of the clearance flow and shaft vibration of the divergent tapered annular seal was performed. In particular, the modeling of the clearance flow of the divergent tapered annular seal was investigated by detailed comparison with CFD analysis of the pre-swirl ratio and loss coefficient at the inlet. Two-way coupled analysis of the clearance flow and shaft vibration of the divergent tapered annular seal incorporating this model was conducted to determine the OSI. The results were compared with experimental results and discussed.