On the Leakage, Torque and Dynamic Force Coefficients of an Air in Oil (Wet) Annular Seal: a CFD Analysis Anchored to Test Data

[+] Author and Article Information
Luis San Andrés

Mast-Childs Chair Professor, Fellow ASME Mechanical Engineering Dept. Texas A&M University, College Station, TX 77843, USA

Jing Yang

Research Associate Mechanical Engineering Dept. Texas A&M University, College Station, TX 77843, USA

Xueliang Lu

Graduate Research Assistant Mechanical Engineering Dept. Texas A&M University, College Station, TX 77843, USA

1Corresponding author.

ASME doi:10.1115/1.4040766 History: Received June 25, 2018; Revised June 28, 2018


Subsea pumps and compressors must withstand multi-phase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content in the primary stream affects the leakage and rotordynamic performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power and rotordynamic coefficients of a smooth annular seal supplied with an air in oil mixture. The CFD seal leakage and drag power decrease steadily as the GVF increases. A multiple-frequency whirl orbit method aids in the calculation of seal rotordynamic coefficients. The injection of air in the oil immediately produces frequency dependent force coefficients; in particular the direct stiffness which hardens with frequency. The effect is most remarkable for small GVFs, as low as 0.2. The predictions of CFD and bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent vibration in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed to safety. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.

Copyright (c) 2018 by ASME
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