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Research Papers: Gas Turbines: Structures and Dynamics

On Occurrence of Reverse Full Annular Rub

[+] Author and Article Information
John J. Yu

GE Energy, 1631 Bently Parkway South, Minden, NV 89423john.yu@ge.com

J. Eng. Gas Turbines Power 134(1), 012505 (Nov 07, 2011) (8 pages) doi:10.1115/1.4004161 History: Received April 17, 2011; Accepted May 01, 2011; Published November 07, 2011; Online November 07, 2011

Abstract

This paper discusses reverse full annular rub based on a two degree-of-freedom rotor/seal model where a rubbing location can be simulated away from the lumped rotor mass. The analytical model is much closer to the experimental setup for comparison of results, and real machines for analysis, than the previous one degree-of-freedom model. Its closed-form solution is given including reverse rub amplitudes and relative phases, as well as the normal contact force. The exact frequency equation in polynomial form yields reverse full annular rub frequencies without having to neglect any parameters. Many conclusions can be drawn directly from explicit expressions without numerical calculations. The solution with nonpositive normal contact force indicates a dry-friction whirl/whip-free region, usually accompanied by low friction and/or high damping. The analytical study covers both dry-friction whirl and dry-friction whip, and their relations with dry-friction factor, damping, and rotor speed. Range of reverse rub frequencies, their relation with rotor and rotor/seal coupled natural frequencies, and direction of frictional force, are also revealed. Destructive dry-friction whip experimental results are given, which have fully confirmed the analytical formulas.

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Figures

Figure 1

Diagram of analytical mode for reverse full annular rub

Figure 2

Valid reverse rub solutions with friction factor μ at D = Ds  = 10 N m/s, ηs  = 0.01; (a) reverse rub frequency ratio − ω/ω0 ; (b) positive nondimensional normal contact force N/(Cr Ks ) and frictional force μN/(Cr Ks ); and (c) ratios of rotor amplitudes to clearance at rotor mass A/Cr and rubbing location Ar /Cr

Figure 3

Valid reverse rub solutions with rotor damping ratio ζ at μ = 0.2, Ds  = 10 N m/s, ηs  = 0.01; (a) reverse rub frequency ratio − ω/ω0 ; (b) positive nondimensional normal contact force N/(Cr Ks ) and frictional force μN/(Cr Ks ); and (c) ratios of rotor amplitudes to clearance at rotor mass A/Cr and rubbing location Ar /Cr

Figure 4

Valid reverse rub solutions in terms of rotor speed Ω at slip friction factor μslip  = 0.2 and rotor damping ratio ζ = 0.025 with rotor radius-to-radial-clearance ratio r/Cr  = 40 for 10 mm diameter shaft; (a) friction factorμ; (b) whirl/whip frequency; (c) normal contact force N and frictional force μN; and (d) rotor peak-to-peak amplitudes at rotor mass 2A and rubbing location 2Ar

Figure 5

Rub experimental setup

Figure 6

Reverse full annular rub (a) triggered at 262 rpm as shown in time base and (b) waterfall plot measured by horizontal probe near seal

Figure 7

Diagram of experimental setup and distance of rotor mass and seal block relative to two bearings

Figure 8

Four seals numbered from 1 to 4

Errata

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