Session: 25-01 Annular Seals 1

Paper Number: 83164

83164 - Experimental Force Coefficients for a Fully-Partitioned Pocket Damper Seal and Comparison to Other Two Seal Types 

Labyrinth seals (LS), honeycomb seals (HCS) and hole-pattern seals, pocket damper seals (PDS) and fully-partitioned damper seals (FPDS) serve as balance pistons on the discharge side of barrel type centrifugal compressors. These seals, facing large pressure differentials along with significant changes in gas density, produce sizeable lateral forces that impact compressor stability and its rotordynamic performance. There is extensive archival data on the dynamic forced performance of LS and textured surface seals. However, the experimental data base for a FPDS is insufficient, thus a comprehensive comparison of their dynamic force performance against that of textured surface seals is missing. The paper presents experimentally derived rotordynamic force coefficients for a FPDS along with a direct comparison to published data for a HCS and a LS, both similar in size and in operating conditions. The dynamic load tests with the FPDS (114.3 mm in diameter, 85.6 mm in length, and clearance = 0.20 mm), include operation at a shaft speed (W) of 15 krpm (rotor surface speed of 90 m/s) while supplied with air at P_in = 70 bar and ambient temperature, and a discharge at P_out = 0.25, 0.5, and 0.65 of P_in. The pre-swirl circumferential velocity at the seal inlet is low, approximately 10% of rotor speed. The FPDS having eight pockets × eight axial blades produces a direct stiffness (K) increasing with excitation frequency (w), though K < 0 for the lowest pressure ratio PR= (P_out / P_in) = ¼. The cross-coupled stiffness (k) is invariant to frequency whereas the direct damping (C) decreases steadily. Hence, the effective damping coefficient (C_eff = C − k/w) is constant for w > 70 Hz (w > 0.28 W ) and not a function of PR. For the three PRs, the FPDS leakage is roughly up to 25% larger than the HCS leakage, while the 20 blade LS leaks in between both. The comparison of results shows the LS has insignificant forces compared to those from the HCS and FPDS, both producing a comparable C_eff and similar cross-over frequencies (C_eff >0). The HCS produces a large direct stiffness (K), three to four times that from the FPDS. Comparison of the FPDS experimental force coefficients against CFD predictions shows significant differences, in particular an over estimation of direct stiffness as the frequency grows along with a lower direct damping for frequencies equal or above the shaft speed. Besides manufacturing considerations, a FPDS is a better alternative to a HCS whose large centering stiffness (K) may affect the compressor critical speed, hence shortening the separation margin with respect to the operating speed.

Presenting Author: Adolfo Delgado Texas A&amp;M University

Presenting Author Biography: Adolfo Delgado is an Associate Professor of Mechanical Engineering at Texas A&amp;M University. His research focuses on rotordynamics, structural vibration, energy dissipation mechanisms, thin film lubrication and fluid structure interaction applied to the design, modeling and improvement of rotating machinery systems and components. Prior to joining Texas A&amp;M, Adolfo was a Research Engineer at the General Electric Global Research Center where he led and worked on multiple initiatives involving improvement of existing rotating equipment and development of new rotor-bearing system architectures and turbomachinery components, such as variable geometry bearings, annular seals, dampers and oil-free bearings. Dr. Delgado received his B.S. in mechanical engineering from Sim&#243;n Bol&#237;var University, and his M.S. and Ph.D. in mechanical engineering from Texas A&amp;M University.

Authors:

Adolfo Delgado Texas A&M University
Luis San Andrés Texas A&M University
Jing Yang Texas A&M University
Jonathan Thiele Rotoflow