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research-article

Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor Liquid Annular Seals Utilizing CFD

[+] Author and Article Information
Farzam Mortazavi

ASME Member, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843
farzam.mortazavi@tamu.edu

Alan Palazzolo

James J. Cain Professor I, ASME Fellow, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843
a-palazzolo@tamu.edu

1Corresponding author.

ASME doi:10.1115/1.4038437 History: Received July 10, 2017; Revised November 01, 2017

Abstract

Circumferentially grooved, annular liquid seals typically exhibit good whirl frequency ratios and leakage reduction, yet their low effective damping can lead to instability. The current study investigates the rotordynamic behavior of a 15 step groove-on-rotor annular liquid seal by means of CFD, in contrast to previous studies which focused on a groove-on-stator geometry. The seal dimensions and working conditions have been selected based on experiments of Moreland and Childs (2016). The precessional frequency ratios as high as 4 have been studied. Implementation of pressure-pressure inlet and outlet conditions obviates the need for loss coefficients at the entrance and exit of the seal. A computationally efficient quasi-steady approach is used to obtain impedance curves as functions of the excitation frequency. The effectiveness of steady-state CFD approach is validated by comparison with the experimental results of Moreland and Childs. Results show good agreement in terms of leakage, pre-swirl ratio and rotordynamic coefficients. It was found that pre-swirl ratio (PSR) will be about 0.3-0.4 at the entrance of seal in the case of radial injection and outlet-swirl ratio (OSR) always converges to values near 0.5 for current seal and operational conditions. The negative value of direct stiffness coefficients, large cross-coupled stiffness coefficients and small direct damping coefficients explain the destabilizing nature of these seals. Finally, influence of surface roughness on leakage, PSR, OSR, and stiffness coefficients is discussed.

Copyright (c) 2017 by ASME
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