Abstract

In this paper a novel bulk-flow model for pocket damper seals (PDS) is introduced. The model is based on two control volumes for each circumferential pocket of the seal. The continuity, circumferential momentum and energy equations are considered for each control volume. The circumferential recirculating flow within the pocket is modelled for the first time. The boundary layer theory is used to estimate the recirculating flow area, and the Swamee-Jain friction factor correlation allows for defining the dissipation of the circumferential velocity. The perturbation method is used to solve the partial derivative governing equations in the zeroth and first-order system of equations. The rotordynamic coefficients are evaluated by integrating the dynamic pressure and rotor shear stresses along the circumferential direction.

The predictions are compared to the experimental data, which refer to test conditions representative of high-pressure centrifugal compressors. Numerical predictions are accurate for both high positive-negative inlet pre-swirl ratios. Leakage predictions are also aligned with measurements.

Finally, sealing selection approach is introduced in the paper for comparing the dynamic behaviour of two different sealing technologies and identifying stable regions as a function of the rotor natural frequency and pre-swirl ratio.

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