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Investigations of Slip Effect on the Performance of Micro Gas Bearings and Stability of Micro Rotor-Bearing Systems

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ABSTRACT

Incorporating the velocity slip effect of the gas flow at the solid boundary, the performance and dynamic response of a micro gas-bearing-rotor system are investigated in this paper. For the characteristic length scale of the micro gas bearing, the gas flow in the bearing resides in the slip regime rather than in the continuum regime. The modified Reynolds equations of different slip models are presented. Gas pressure distribution and load carrying capacity are obtained by solving the Reynolds equations with finite different method (FDM). Comparing results from different models, it is found that the second order slip model agrees reasonably well with the benchmarked solutions obtained from the linearized Boltzmann equation. Therefore, dynamic coefficients derived from the second order slip model are employed to evaluate the linear dynamic stability and vibration characteristics of the system. Compared with the continuum flow model, the slip effect reduces dynamic coefficients of the micro gas bearing, and the threshold speed for stable operation is consequently raised. Also, dynamic analysis shows that the system responses change with variation of the operating parameters including the eccentricity ratio, the rotational speed, and the unbalance ratio.

No MeSH data available.


Schematic cross-section of the micro-motor integrated with gas bearing.
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f1-sensors-07-01399: Schematic cross-section of the micro-motor integrated with gas bearing.

Mentions: In an attempt to address the ever rising demand for high performance compact power source, a new branch of micro-electro-mechanical system called power MEMS has recently been defined[1, 2]. Among them, the nascent project to develop micro scale gas turbine generators at MIT is specifically targeted for high power density applications. These machines are supported by gas bearings, as shown in Fig.1, and able to achieve rotation rate of more than one million RPM (revolutions per minute)[2]. The micro rotor and the micro bearing are fabricated by micro fabrication technology. Different from the traditional rotor system, the micro rotor and the bearing are made of Silicon.


Investigations of Slip Effect on the Performance of Micro Gas Bearings and Stability of Micro Rotor-Bearing Systems
Schematic cross-section of the micro-motor integrated with gas bearing.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814859&req=5

f1-sensors-07-01399: Schematic cross-section of the micro-motor integrated with gas bearing.
Mentions: In an attempt to address the ever rising demand for high performance compact power source, a new branch of micro-electro-mechanical system called power MEMS has recently been defined[1, 2]. Among them, the nascent project to develop micro scale gas turbine generators at MIT is specifically targeted for high power density applications. These machines are supported by gas bearings, as shown in Fig.1, and able to achieve rotation rate of more than one million RPM (revolutions per minute)[2]. The micro rotor and the micro bearing are fabricated by micro fabrication technology. Different from the traditional rotor system, the micro rotor and the bearing are made of Silicon.

View Article: PubMed Central

ABSTRACT

Incorporating the velocity slip effect of the gas flow at the solid boundary, the performance and dynamic response of a micro gas-bearing-rotor system are investigated in this paper. For the characteristic length scale of the micro gas bearing, the gas flow in the bearing resides in the slip regime rather than in the continuum regime. The modified Reynolds equations of different slip models are presented. Gas pressure distribution and load carrying capacity are obtained by solving the Reynolds equations with finite different method (FDM). Comparing results from different models, it is found that the second order slip model agrees reasonably well with the benchmarked solutions obtained from the linearized Boltzmann equation. Therefore, dynamic coefficients derived from the second order slip model are employed to evaluate the linear dynamic stability and vibration characteristics of the system. Compared with the continuum flow model, the slip effect reduces dynamic coefficients of the micro gas bearing, and the threshold speed for stable operation is consequently raised. Also, dynamic analysis shows that the system responses change with variation of the operating parameters including the eccentricity ratio, the rotational speed, and the unbalance ratio.

No MeSH data available.