题 目：Study of Cavitation in an Oscillatory Oil Squeeze Film

时 间：2007年11月16日（星期五）下午2： 30

地 点：3308维多利亚线路检测中心第三会议室

报告人：孙大成教授 Department of Mechanical Engineering

State University of New York

Study of Cavitation in an Oscillatory Oil Squeeze Film

The mechanism of oil film cavitation in dynamically loaded bearings is presently not well understood. Nowadays the prevailing method to analyze the performance of these bearings is the use of various “cavitation algorithms” based on the JFO theory. This method does not reveal the occurrence of tensile stresses in the oil film, whereas many measured results showed the contrary. In this study we propose a new model of dynamic cavitation that allows the occurrence of tensile stresses in the oil film. This is achieved by replacing the zero pressure-gradient boundary condition at the rupture boundary, which is used in various existing cavitation algorithms, with a flow continuity condition. The proposed cavitation model is applied to a parallel-plate oil squeeze film. This configuration is chosen because it is simple and allows many solution features brought out analytically. One is the discovery that the zero pressure-gradient boundary condition not only eliminates tensile stresses in the oil film, but also results in an instant finite-size cavitation region.

To test the validity of the proposed cavitation model, we built a parallel-plate oil squeeze film test rig to measure pressure traces in the oil film and simultaneously photograph cavitation development. We compared the measured results case by case with the model prediction, and achieved some preliminary successes. Among the findings are: (a) When cavitation did not occur, the measured pressure traces agreed well with the theory of non-cavitated oil squeeze film. In particular, tensile stresses of significant magnitudes were measured in the oil film. (b) When cavitation occurred, the measured pressure traces agreed well with the prediction of the proposed model. In particular, tensile stresses were measured in the oil film before the arrival of the expanding cavitation front.

To address the issue that two types of oil film behavior (non-occurrence and occurrence of cavitation) both existed at apparently the same bearing operating conditions, we made a preliminary analysis of the size effect of cavitation nuclei, which are believed to be the tiny air bubbles entrained or otherwise existed in the oil film. The analysis shows that the oil film’s ability to sustain tensile stresses indeed depends on the size of cavitation nuclei. If cavitation nuclei are small (say, in the sub-micrometer range), it is unlikely that oil squeeze films would cavitate; on the other hand, if the nuclei grow to the sub-millimeter range, oil films would cavitate near the absolute-zero pressure level.

In the experiment we also observed a trend that, under the same operating conditions, an uncavitated oil film would tend to become cavitated, and initially measured tensile stresses would tend to disappear after more oscillations. We believe this had also to do with the size of cavitation nuclei, which might grow due to more air entrainment or merge as they roam around in the oil film. The observation was not in accord with an earlier one made in a journal bearing, where the non-occurrence or occurrence of cavitation was quite persistent once a type of behavior was established. We believe the discrepancy was due to the difference in bearing configuration. In a journal bearing with horizontal bearing axis the entrained air bubbles tend to accumulate in the top part of the bearing clearance, whereas in a horizontal oil film they can migrate from one place to another causing the drift in oil film behavior.

D. C. SUN, Professor

Department of Mechanical Engineering

State University of New York at Binghamton

Binghamton, New York 13902-6000

EDUCATION

Taiwan University, BS 1959 Department of Civil Engineering

Taipei, Taiwan

University of Kansas, MS 1963 Department of Mechanics and Aerospace

Lawrence, Kansas Engineering

Princeton University, MA 1965 Department of Aerospace and Mechanical

Princeton, New Jersey Sciences

Princeton University, PhD 1969 Department of Aerospace and Mechanical

Princeton, New Jersey Sciences

PROFESSIONAL SOCIETIES

Fellow, Society of Tribologists and Lubrication Engineers

Fellow, American Society of Mechanical Engineers

Associate Editor, Journal of Tribology (1985.8 - 1991.6)

Member, Tribology Division Executive Committee (1993.5 - 1997.5)

Chair, Tribology Division Executive Committee (1996.7 - 1997.5)

Member, Research Committee on Tribology (1992.6 - 1998.6)

Chair, Honors and Awards Committee, Tribology Division (1999 - 2000)

流体润滑及摩擦学领域国际知名专家，在多家公司和大学从事过研究工作，在ASME等国际期刊上发表论文数十篇。

欢迎有兴趣的研究生届时听讲座。研究生计学分。

3308维多利亚线路检测中心研究生教学办

2007-11-8