Identification of Friction Factors for Modelling the Exciting Forces caused by Flow in Labyrinth Seals

Variation of Fluid Flow Forces in Seals With Rotor Bending

Volume 3B: 15th Biennial Conference on Mechanical Vibration and Noise — Acoustics, Vibrations, and Rotating Machines ◽

10.1115/detc1995-0527 ◽

1995 ◽

Author(s):

K. Kwanka

Keyword(s):

Stability Limit ◽

Mode Shapes ◽

Flexible Rotor ◽

Labyrinth Seals ◽

Identification Procedure ◽

Dynamic Coefficients ◽

Exciting Forces ◽

Direct Stiffness ◽

The Stability ◽

Turbomachine Rotor

Abstract Fluid-induced forces in labyrinth seals can cause unstable self-excited vibrations of the turbomachine rotor. Generally, a linear approach employing dynamic coefficients is used to describe these forces. A new procedure for the identification of the coefficients which uses two excitation sources placed on a flexible rotor is presented. The change in the stability limit and vibrational frequency caused by the investigated labyrinth gas seal contains the dynamic coefficients. It is important that problems which may also occur in the real turbomachine are considered by the identification procedure. The conservative dynamic coefficients, such as the direct stiffness, influence the bending of the mode shapes and thus affect indirectly the stability limit. The magnitude of the exciting forces depends on the axial positioning of the excitation source and also on the mode shape bending. These two dependencies are investigated by experiment and considered in the identification procedure.

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CJ90-36. A study of the fluid exciting forces and dynamic characteristic coefficients of labyrinth seals

International Journal of Mechanical Sciences ◽

10.1016/0020-7403(90)90071-p ◽

1990 ◽

Vol 32 (11) ◽

pp. 961

Keyword(s):

Dynamic Characteristic ◽

Labyrinth Seals ◽

Exciting Forces

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Gas labyrinth seals: On the effect of clearance and operating conditions on wall friction factors – A CFD investigation

Tribology International ◽

10.1016/j.triboint.2018.10.046 ◽

2019 ◽

Vol 131 ◽

pp. 363-376 ◽

Cited By ~ 7

Author(s):

Tingcheng Wu ◽

Luis San Andrés

Keyword(s):

Operating Conditions ◽

Wall Friction ◽

Labyrinth Seals ◽

Friction Factors

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Protecting Turbomachinery From Self-Excited Rotor Whirl

Journal of Engineering for Power ◽

10.1115/1.3678270 ◽

1965 ◽

Vol 87 (4) ◽

pp. 333-343 ◽

Cited By ~ 132

Author(s):

J. S. Alford

Keyword(s):

Tip Clearance ◽

Design Parameters ◽

Labyrinth Seals ◽

Disturbing Force ◽

Rotor Systems ◽

Axial Compressors ◽

Exciting Forces ◽

Blade Tip ◽

Deflection Criteria ◽

Blade Tip Clearance

Aerodynamic exciting forces have caused severe rotor whirl of axial compressors and turbines. One disturbing force investigated is due to circumferential variation of static pressure acting on the cylindrical surface of rotor, particularly within labyrinth seals. Another aerodynamic disturbing force is due to eccentricity of rotor causing circumferential variation of blade-tip clearance, and a corresponding variation of local efficiency and unbalanced torque. Seal deflection criteria and torque deflection criteria are presented as design guides for stable rotor systems. These criteria, the form of which comes from analysis of rotor dynamics, correlate design parameters of four examples of unstable rotor systems which exhibited whirl.

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A Method for Calculating Labyrinth Seal Inlet Swirl Velocity

Journal of Vibration and Acoustics ◽

10.1115/1.2930519 ◽

1990 ◽

Vol 112 (3) ◽

pp. 380-383 ◽

Cited By ~ 9

Author(s):

R. Gordon Kirk

Keyword(s):

Dynamic Stiffness ◽

Axial Flow ◽

Radial Pressure ◽

Labyrinth Seal ◽

Pressure Gradients ◽

Labyrinth Seals ◽

Friction Factors ◽

Swirl Velocity ◽

Vortex Solution ◽

Inlet Swirl

The results of numerous investigators have shown the importance of inlet swirl on the calculated dynamic stiffness and stability of labyrinth seals. These results have not included any calculation of inlet leakage of swirl as a function of complex disk geometry including the sealing conditions of the given seal. This paper outlines a method of calculating the inlet swirl at the entrance of the labyrinth seal by introducing a radial chamber which when added to the axial flow solution allows the prediction of the gas swirl as it flows radially from the stage tip along the disk face inward to the seal location. This solution is consistent with the leakage model for the seal and allows rapid evaluation of seal designs. For a centrifugal compressor, this added feature permits the designer to include the flow path from the impeller discharge, down the back of the disk or front of the cover, then into the shaft seal or eye packing, respectively. The solution includes the friction factors of both the disk and stationary wall with account for mass flow rate and calculation of radial pressure gradients by a free vortex solution. The results of various configurations are discussed and comparisons made to other published results of disk circumferential velocity swirl.

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