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Research Papers: Gas Turbines: Structures and Dynamics

Rigid Mode Vibration Control and Dynamic Behavior of Hybrid Foil–Magnetic Bearing Turbo Blower

[+] Author and Article Information
Sena Jeong

Center for Urban Energy Research,
Korea Institute of Science and Technology,
Seoul 02792, South Korea
e-mail: senaj@kist.re.kr

Doyoung Jeon

Department of Mechanical Engineering,
Sogang University,
Seoul 04107, South Korea
e-mail: dyjeon@sogang.ac.kr

Yong Bok Lee

Center for Urban Energy Research,
Korea Institute of Science and Technology,
Seoul 02792, South Korea
e-mail: lyb@kist.re.kr

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 12, 2016; final manuscript received August 17, 2016; published online November 22, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(5), 052501 (Nov 22, 2016) (12 pages) Paper No: GTP-16-1405; doi: 10.1115/1.4034920 History: Received August 12, 2016; Revised August 17, 2016

In this study, experimental and analytical analyses of the vibration stability of a 225 kW class turbo blower with a hybrid foil–magnetic bearing (HFMB) were performed. First, critical speed and unbalance vibration responses were examined as part of the rotordynamic research. Its shaft diameter was 71.5 mm, its total length was 693 mm, and the weight of the rotor was 17.8 kg. The air foil bearing (AFB) utilized was 50 mm long and had a 0.7 aspect ratio. In the experiments conducted, excessive vibration and rotor motion instability occurred in the range 12,000–15,000 rpm, which resulted from insufficient dynamic pressure caused by the length of the foil bearing being too short. Consequently, as the rotor speed increased, excessive rotor motion attributable to aerodynamic and bearing instability became evident. This study therefore focused on improving rotordynamic performance by rectifying rigid mode unstable vibration at low speed, 20,000 rpm, and asynchronous vibration due to aerodynamic instability by using HFMB with vibration control. The experimental results obtained were compared for each bearing type (AFB and HFMB) to improve the performance of the vibration in the low-speed region. The experimental results show that the HFMB technology results in superior vibration stability for unbalance vibration and aerodynamic instability in the range 12,000–15,000 rpm (200–250 Hz). The remarkable vibration reduction achieved from vibration control of the HFMB–rotor system shows that oil-free turbomachinery can achieve excellent performance.

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Figures

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Fig. 1

Structure of the HFMB in the 225 kW class turbo blower system

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Fig. 2

The AFB designed for the turbo blower system: (a) air foil journal bearing and (b) air foil thrust bearing with eight pads and bump layer

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Fig. 3

AFB characteristics' analysis results minimum film thickness with bearing length changes

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Fig. 4

AFB characteristics' analysis results with bearing length changes: (a) direct stiffness coefficients and (b) cross coupled stiffness coefficients

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Fig. 5

Detailed structure of the air foil and magnetic bearings: (a) AFB and bump geometry and (b) heteropolar radial AMB

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Fig. 6

AFB characteristics' analysis results with bearing length changes: (a) direct damping coefficients and (b) cross coupled damping coefficients

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Fig. 7

Block diagram of closed-loop magnetic bearing control system

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Fig. 8

Predicted equivalent stiffness and damping of AMB for various proportional control gain changes

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Fig. 9

Natural frequency simulation results and mode shapes in predicted AFB dynamics at L/D = 0.7

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Fig. 10

Damped analysis results for AFB turbo blower: (a) Campbell diagram and (b) damping ratio of stability map

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Fig. 11

Impact test frequency response results for AFB and AMB

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Fig. 12

Levitation responses of the HFMB for various kP gains (Td was fixed at 460 μs, zero rotor speed): (a) X direction position responses, (b) Y direction position responses, and (c)trajectory of rotor

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Fig. 14

Vibration trajectory comparison according to the control gain changes at the rigid mode speed of AFB

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Fig. 16

Waterfall data comparison in accordance with magnetic effect application: (a) horizontal FFT data for AFB support, (b) vertical FFT data for AFB support, (c) horizontal FFT data for AMB turned on and off, and (d) vertical FFT data for AMB turned on and off during rotor operation

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Fig. 15

Vibration trajectory comparison according to rotating speed: (a) AMB turned on at 14,400 rpm, (b) HFMB operation in AFB mode range, (c) AMB turned off at 17,520 rpm, and (d) AFB's stable operation at 20,000 rpm

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Fig. 13

Orbital vibration experimental results for rigid mode vibration of the AFB with and without magnetic effect (including all synchronous vibrations)

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