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

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.


Comparison of the load carrying capacity
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f6-sensors-07-01399: Comparison of the load carrying capacity

Mentions: For the micro gas bearing presented in this discussion, the non-dimensional flow rate is compared in Fig.4 where the eccentricity ratio ranges from 0.1 to 0.99. It can be seen that the second order slip model excels others in the sense of approximation to the linearized Boltzmann equation in the overall operational range. When the eccentricity ratio is less than 0.9, the result of the first order slip model is also acceptable. Figure 5 depicts the gas pressure distributions of the gas film when the eccentricity ratio is 0.95 and the bearing number is 5. It is noted that results of the second order slip model are almost the same as that of the linearized Boltzmann equation, while the first order and the 1.5 order slip models overestimate the gas pressure. Consequently, the load capacities are overestimated and the attitude angles are underestimated, as shown in Fig.6 and Fig.7 respectively.


Investigations of Slip Effect on the Performance of Micro Gas Bearings and Stability of Micro Rotor-Bearing Systems
Comparison of the load carrying capacity
© Copyright Policy
Related In: Results  -  Collection

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

f6-sensors-07-01399: Comparison of the load carrying capacity
Mentions: For the micro gas bearing presented in this discussion, the non-dimensional flow rate is compared in Fig.4 where the eccentricity ratio ranges from 0.1 to 0.99. It can be seen that the second order slip model excels others in the sense of approximation to the linearized Boltzmann equation in the overall operational range. When the eccentricity ratio is less than 0.9, the result of the first order slip model is also acceptable. Figure 5 depicts the gas pressure distributions of the gas film when the eccentricity ratio is 0.95 and the bearing number is 5. It is noted that results of the second order slip model are almost the same as that of the linearized Boltzmann equation, while the first order and the 1.5 order slip models overestimate the gas pressure. Consequently, the load capacities are overestimated and the attitude angles are underestimated, as shown in Fig.6 and Fig.7 respectively.

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.