Abstract

Understanding the leakage and rotordynamic performance of a hole-pattern annular seal is critical to the design of a centrifugal pump regarding vibration characteristics and stability. The growing interest in 2-phase pumping, handling gas components in the oil stream directly, brings more challenges to pump design. This paper studies the leakage and rotordynamic performance of a hole-patten annular seal under bubbly (oil/air) flow conditions. The test seal’s length-to-diameter ratio is 0.75. The rotor surface is smooth, and the seal inner surface is textured (65% of the area is occupied by round holes with a depth of 2.5 mm). The test fluid is comprised of silicone oil and air, and the gas volume fraction GVF at the seal inlet is from zero to 9.3%. Tests also cover two pressure drops (44.8 and 55.1 bars) and three rotor speeds (5, 10, and 15 krpm). Test results showed that adding air to the oil (inlet GVF up to 9.3%) has a small impact on mass flow leakage. Mass flow leakage increases slightly (by ∼4%) as inlet GVF increases from zero to 3.4% and then decreases slightly (by < 5%) as inlet GVF is further increased to 9.3%. As inlet GVF increases, measured values of direct stiffness K, direct damping C, cross-coupled damping c, and direct virtual-mass M decrease. Adding air to the oil (inlet GVF up to 9.3%) shows no obvious impact on measured cross-coupled stiffness k and measured effective damping Ceff. Measurements are also used to examine San Andres’s bulk-flow model (2011, “Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals,” ASME J. Eng. Gas Turbines Power, 134(2), p. 022503). The model shows limited capability in predicting the performance of the hole-pattern seal under mainly-oil conditions. The discrepancy between the experimental results and theoretical predictions calls for more improvements in the predictive model to handle hole-pattern seals with mainly-oil mixtures.

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