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Research Papers: Other (Seals, Manufacturing)

Steady-State Response of a Flexibly Mounted Stator Mechanical Face Seal Subject to Dynamic Forcing of a Flexible Rotor

[+] Author and Article Information
Philip Varney

Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318
e-mail: pvarney3@gatech.edu

Itzhak Green

Professor
Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30318
e-mail: itzhak.green@me.gatech.edu

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received May 9, 2016; final manuscript received March 25, 2017; published online June 14, 2017. Assoc. Editor: Mihai Arghir.

J. Tribol 139(6), 062201 (Jun 14, 2017) (9 pages) Paper No: TRIB-16-1157; doi: 10.1115/1.4036380 History: Received May 09, 2016; Revised March 25, 2017

Mechanical face seals are constitutive components of much larger turbomachines and require consideration of the system dynamics for successful design. The dynamic interplay between the seal and rotor is intensified by recent trends toward reduced clearances, higher speeds, and more flexible rotors. Here, the “rotor” consists of the flexible shaft and the rotating seal seat. The objective here is to, for the first time, determine how the rotor affects the seal performance and vice versa. Thresholds can then be established beyond which the rotor influences the seal but not vice versa (i.e., the rotordynamics can be sent to the seal analysis as an exogenous input). To this end, a model of a flexibly mounted stator face seal is provided including the coupled dynamics of the flexible rotor. The model accounts for axial and angular deflections of the rotor and seal. Coupled rotordynamics are modeled using a lumped-parameter approach including static and dynamic rotor angular misalignments. For expediency, linearized expressions for fluid forces are used, and the resulting steady-state equations of motion are solved analytically to investigate how rotor inertia, speed, and angular misalignment influence the coupled seal dynamics. Importantly, results from the study reveal that in some operating regimes, neglecting the rotordynamics implies healthy seal operation when instead intermittent rub exists between the faces. This work also shows that when the rotor inertia is much larger than the seal inertia, the rotordynamics can be solved separately and used in the seal model as an external input.

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References

Figures

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Fig. 1

FMS seal configuration showing the flexible rotor and stationary seal element

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Fig. 2

Reference frames used to model the kinematics of a flexibly mounted stator mechanical face seal

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Fig. 3

Comparing the numeric solution of the full nonlinear equations of motion to the analytic solution of the linearized equations of motion (δ = 2)

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Fig. 4

Investigating the influence of FMS dynamics on rotor response for an angular misalignment of χ=0.5 mrad, δ = 2

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Fig. 5

Relative tilt versus rotor–stator inertia ratio for thin and thick rotors: (a) thick rotor (δ = 2) and (b) thin rotor (δ = 0.5)

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Fig. 6

Relative tilt versus shaft speed for several values of angular misalignment, highlighting the appearance of face contact when coupled rotordynamics are included (δ=2,Itr/Its=50)

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Fig. 7

Relative tilt versus shaft speed ωr and rotor inertia ratio δ=Itr/Ipr (χ = 0.5 mrad): (a) case when the rotor inertia is much larger than the FMS (Itr/Its  = 50) and (b) case when the rotor inertia is comparable to the FMS (Itr/Its  = 2)

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