Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor Liquid Annular Seals Utilizing Computational Fluid Dynamics

Author:

Mortazavi Farzam1,Palazzolo Alan2

Affiliation:

1. Mem. ASME Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843 e-mail:

2. Fellow ASME Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843 e-mail:

Abstract

Circumferentially grooved, annular liquid seals typically exhibit good whirl frequency ratios (WFRs) 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 computational fluid dynamics (CFD), in contrast to the 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, “Influence of Pre-Swirl and Eccentricity in Smooth Stator/Grooved Rotor Liquid Annular Seals, Measured Static and Rotordynamic Characteristics,” M.Sc. thesis, Texas A&M University, College Station, TX). The frequency ratios as high as four have been studied. Implementation of pressure-pressure inlet and outlet conditions make the need for loss coefficients at the entrance and exit of the seal redundant. 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, preswirl ratio (PSR), and rotordynamic coefficients. It was found that PSR will be about 0.3–0.4 at the entrance of the 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 explains the destabilizing nature of these seals. Finally, the influence of surface roughness on leakage, PSR, OSR, and stiffness coefficients is discussed.

Publisher

ASME International

Subject

General Engineering

Reference32 articles.

1. Dynamic Response Analysis of Balance Drum Labyrinth Seal Groove Geometries Optimized for Minimum Leakage;ASME J. Vib. Acoust.,2017

2. Moreland, J. A., and Childs, D. W., 2016, “Influence of Pre-Swirl and Eccentricity in Smooth Stator/Grooved Rotor Liquid Annular Seals, Measured Static and Rotordynamic Characteristics,” M.Sc. thesis, Texas A&M University, College Station, TX. http://oaktrust.library.tamu.edu/handle/1969.1/158918

3. Massey, I., 1985, “Subsynchronous Vibration Problems in High-Speed Multistage Centrifugal Pumps,” 14th Turbomachinery Symposium, Houston, TX, Oct., pp. 11–16.http://oaktrust.library.tamu.edu/handle/1969.1/163638

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