1999 Fiscal Year Final Research Report Summary
A New Theoretical Model and Dynamic Characteristics of Two-Phase Oil Film Flow in Very High Speed Journal Bearing
| Project/Area Number |
09305014
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
設計工学・機械要素・トライボロジー
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| Research Institution | THE UNIVERSITY OF TOKYO |
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Principal Investigator |
TANAKA Masato THE UNIVERSITY OF TOKYO GRADUATE SCHOOL OF ENGINEERING, PROFESSOR, 大学院・工学系研究科, 教授 (10011131)
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| Co-Investigator(Kenkyū-buntansha) |
SUGIMOTO Jutarou THE UNIVERSITY OF TOKYO GRADUATE SCHOOL OF ENGINEERING, RESEARCH ASSISTANT, 大学院・工学系研究科, 助手 (20114514)
FUKUSIMA Yoshiaki THE UNIVERSITY OF TOKYO GRADUATE SCHOOL OF ENGINEERING, RESEARCH ASSISTANT, 大学院・工学系研究科, 助手 (20011075)
SUZUKI Kenji THE UNIVERSITY OF TOKYO GRADUATE SCHOOL OF ENGINEERING, LECTURER, 大学院・工学系研究科, 講師 (50251351)
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| Project Period (FY) |
1997 – 1999
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| Keywords | hydrodynamic lubrication / two-phase flow / journal bearing / cavitation / axial oil film rupture / dynamic characteristics / stability / visualization |
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| Research Abstract |
Floating bush journal bearings, widely used turbochargers, show unique stability behavior, and a rotor supported in the bearings can be in stable operation at very high shaft speeds. However conventional theoretical models predict that self-excited vibration of rotor always occurs at such high shaft speeds.
A new theoretical model is presented to investigate the static and dynamic performance of hydrodynamic lubricating film in very high-speed journal bearings. This model can incorporate the effect of centrifugal force acting on the oil film due to the high speed operation, and predicts that two-phase (gas/liquid) oil film flow occurs partially in the inner oil film of floating bush journal bearing. This partial two-phase film is found to decrease the bush-to-journal speed ration. This model also can give the rotordynamic coefficients of the oil film with the partial two-phase flow, which conventional models could not. The decreasing bush-to-journal speed ratio and the partial two-phase flow are found to decrease the rotordynamic coefficients with increasing shaft speeds, resulting in enlarging stable operation region of the bearing at very high shaft speeds. Consequently, this new theoretical model can give a reasonable explanation to the unique stability behavior of floating bush journal bearing which previous theoretical models could not.
However this new theoretical model is based on the assumption of the partial two-phase flow in the oil film yet to be confirmed. Experiments were carried out to observe the behavior of the oil film in transparent journal bearings operating at very high shaft speeds. The oil film behavior was recorded by means of high speed digital video camera and anlysed, and the oil film was found to rupture axi-symmetrically towards the end of the bearing, depending on the operating conditions. The measurements were in good agreement with predictions of the present model.
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