Stability Enhancement of High-speed Rotors on Foil Bearings with the Automatic Mode Switch

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

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An experimental investigation of a microturbine simulated rotor supported on multileaf gas foil bearings with backing bump foils

Proceedings of the Institution of Mechanical Engineers Part J Journal of Engineering Tribology ◽

10.1177/1350650117725463 ◽

2017 ◽

Vol 232 (9) ◽

pp. 1169-1180 ◽

Cited By ~ 5

Author(s):

Bo Zhang ◽

Shemiao Qi ◽

Sheng Feng ◽

Haipeng Geng ◽

Yanhua Sun ◽

...

Keyword(s):

High Speed ◽

Preliminary Test ◽

Journal Bearings ◽

Rotating Machinery ◽

System Stability ◽

Test Rig ◽

Thrust Bearings ◽

Foil Bearings ◽

Simulated System ◽

First Time

Two multileaf gas foil journal bearings with backing bump foils and one set of gas foil thrust bearings were designed, fabricated, and used in a 100 kW class microturbine simulated rotor system to ensure stability of the system. Meanwhile, a preliminary test rig had been built to verify the simulated system stability. The rotor synchronous and subsynchronous responses were well controlled by using of the gas foil bearings. It is on the multileaf gas foil bearings with backing bump foils that the test was conducted and verified for the first time in open literatures. The success in the experiments shows that the design and fabrication of the rotor and the gas foil bearings can provide a useful guide to the development of the advanced high speed rotating machinery.

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Analysis of high speed permanent magnet synchronous motor rotor supported by air foil bearings

International Journal of Applied Electromagnetics and Mechanics ◽

10.3233/jae-171157 ◽

2019 ◽

Vol 59 (2) ◽

pp. 755-764

Author(s):

Hao Lin ◽

Haipeng Geng ◽

Tingchen Du ◽

Xiangming Xu ◽

Yanyan Zhang ◽

...

Keyword(s):

Permanent Magnet ◽

High Speed ◽

Permanent Magnet Synchronous Motor ◽

Synchronous Motor ◽

Foil Bearings

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High-speed two-mode switch for mode-division multiplexing optical networks

Optica ◽

10.1364/optica.4.001098 ◽

2017 ◽

Vol 4 (9) ◽

pp. 1098 ◽

Cited By ~ 49

Author(s):

Yule Xiong ◽

Rubana B. Priti ◽

Odile Liboiron-Ladouceur

Keyword(s):

Optical Networks ◽

High Speed ◽

Mode Switch ◽

Mode Division Multiplexing

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Stability Enhancement of Supercavitating Projectiles by Unsteady Air Injection

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 2 ◽

10.1115/omae2005-67045 ◽

2005 ◽

Author(s):

Yasmin Khakpour ◽

Miad Yazdani

Keyword(s):

Numerical Simulation ◽

Drag Reduction ◽

High Speed ◽

The Body ◽

Air Injection ◽

Cavity Surface ◽

The Stability ◽

Stability Enhancement

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile’s motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is injecting of the air into the cavity unsteadily which varies through the projectile’s surface. This approach is provided by arrays of slots distributed on the projectile’s surface and unsteady injection is modeled over the surface. Furthermore, the position of ventilation, dramatically affects the stability like those in aerodynamics. In all approaches it is assumed that the supercavity covers the whole of the body, however the forces caused by the wakes, formed behind the body are taken into account. The calculation is performed at three cavitation numbers with respective velocities of 40 m/s, 50 m/s, 60 m/s.

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Rotordynamics Performance of Hybrid Foil Bearing Under Forced Vibration Input

Volume 7A: Structures and Dynamics ◽

10.1115/gt2017-65233 ◽

2017 ◽

Author(s):

Daejong Kim ◽

Brian Nicholson ◽

Lewis Rosado ◽

Garry Givan

Keyword(s):

Impulse Response ◽

High Speed ◽

Load Capacity ◽

Supply System ◽

Forced Response ◽

Experimental Results ◽

Lateral Acceleration ◽

Foil Bearings ◽

Foil Bearing ◽

Gas Supply

Foil bearings are one type of hydrodynamic air/gas bearings but with a compliant bearing surface supported by structural material that provides stiffness and damping to the bearing. The hybrid foil bearing (HFB) in this paper is a combination of a traditional hydrodynamic foil bearing with externally-pressurized air/gas supply system to enhance load capacity during the start and to improve thermal stability of the bearing. The HFB is more suitable for relatively large and heavy rotors where rotor weight is comparable to the load capacity of the bearing at full speed and extra air/gas supply system is not a major added cost. With 4,448N∼22,240N thrust class turbine aircraft engines in mind, the test rotor is supported by HFB in one end and duplex rolling element bearings in the other end. This paper presents experimental work on HFB with diameter of 102mm performed at the US Air force Research Laboratory. Experimental works include: measurement of impulse response of the bearing to the external load corresponding to rotor’s lateral acceleration of 5.55g, forced response to external subsynchronous excitation, and high speed imbalance response. A non-linear rotordynamic simulation model was also applied to predict the impulse response and forced subsynchronous response. The simulation results agree well with experimental results. Based on the experimental results and subsequent simulations, an improved HFB design is also suggested for higher impulse load capability up to 10g and rotordynamics stability up to 30,000rpm under subsynchronous excitation.

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Rotordynamic Performance of a Shaft With Large Overhung Mass Supported by Foil Bearings

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4034918 ◽

2016 ◽

Vol 139 (4) ◽

Cited By ~ 2

Author(s):

Nguyen LaTray ◽

Daejong Kim

Keyword(s):

High Speed ◽

Foil Bearings ◽

Speed Test ◽

Foil Bearing ◽

Stable Conditions ◽

Bending Mode ◽

Mode Vibration ◽

Lift Off ◽

Compact Design ◽

Bearing System

This work presents the theoretical and experimental rotordynamic evaluations of a rotor–air foil bearing (AFB) system supporting a large overhung mass for high-speed application. The proposed system highlights the compact design of a single shaft rotor configuration with turbomachine components arranged on one side of the bearing span. In this work, low-speed tests up to 45 krpm are performed to measure lift-off speed and to check bearing manufacturing quality. Rotordynamic performance at high speeds is evaluated both analytically and experimentally. In the analytical approach, simulated imbalance responses are studied using both rigid and flexible shaft models with bearing forces calculated from the transient Reynolds equation along with the rotor motion. The simulation predicts that the system experiences small synchronous rigid mode vibration at 20 krpm and bending mode at 200 krpm. A high-speed test rig is designed to experimentally evaluate the rotor–air foil bearing system. The high-speed tests are operated up to 160 krpm. The vibration spectrum indicates that the rotor–air foil bearing system operates under stable conditions. The experimental waterfall plots also show very small subsynchronous vibrations with frequency locked to the system natural frequency. Overall, this work demonstrates potential capability of the air foil bearings in supporting a shaft with a large overhung mass at high speed.

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