Xue-song Li 1 e-mail: xs-li@mail.tsinghua.edu.cn Yin Song Zeng-rong Hao Chun-wei Gu Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University, Beijing 100084, People’s Republic of China Cavitation Mechanism of Oil-Film Bearing and Development of a New Gaseous Cavitation Model Based on Air Solubility Cavitation phenomenon in lubricants significantly influences the performance of associ- ated machinery. In this paper, the cavitation mechanism of an oil-film bearing is attrib- uted to gaseous cavitation, and a new gaseous cavitation model based on air solubility in the lubricant is presented. The model is validated using the Reynolds equation algorithm for fixed-geometry oil-film journal bearing, and the predicted results at different eccen- tricity ratios show good agreement with published data. The analyses show that gaseous mechanism can explain the cavitation phenomena that occur in the bearing except for very heavy load cases. In particular, this new model is compatible with the Jakobsson–Floberg–Olsson condition. Therefore, the new model has an explicit physical meaning, can produce good results, can identify whether vaporous cavitation occurs, and more importantly, can provide a novel means of developing cavitation models for low- vapor-pressure lubricants. [DOI: 10.1115/1.4006702] Keywords: cavitation model, solubility of air in lubricants, the oil-film bearing, the Reynolds equation 1 Introduction Cavitation is a very important phenomenon in liquid flow, which causes oil-film rupture in bearings and considerably affects their performance. Therefore, many cavitation models, such as the classical half-Sommerfeld, the Reynolds, and the Jakobsson– Floberg–Olsson (JFO)-type cavitation models [1,2] have been developed (the latter is based on JFO condition). Although the half-Sommerfeld model does not consider cavitation into account in resolving the pressure field, it is still widely employed because of its simplicity. The Reynolds condition introduces a film-rupture boundary condition but does not give a description of the film ref- ormation. The JFO cavitation theory provides film-rupture and film-reformation conditions and is mass conserving. Various algo- rithms are available for the JFO-type models, like Elrod’s (1981) famous cavitation algorithm [3] and the further developed ver- sions by his many successors, such as Vijayaraghavan and Keith (1989) [4] and Kumar and Booker (1991) [5]. Bonneau et al. (1995) [6] also developed a new cavitation model by combining Murty’s [7] model with the JFO cavitation condition. These Elrod-type methods are widely used in such complex applications as cavitation in dimples [8,9]. The previously mentioned models are based on the observed or measured cavitation rules; however, they do not consider the physical mechanism of cavitation. In reality, physical cavitation mechanism can be realized in two basic forms: vaporous and gaseous. If the pressure in a liquid drops to its vapor pressure, the liquid would boil, causing vaporous cavitation. For liquid with higher vapor pressure, such as water, vaporization plays a major role during cavitation. One of the characteristics of the vaporous cavi- tation is that it occurs at a certain pressure—the vapor pressure— because it is a phase-change process. Another important charac- teristic is that it may initiate cavitation erosion, resulting in severe damage to the solid surface. Vaporous cavitation is complex and difficult to simulate. The classical Rayleigh–Plesset cavitation model and its improved series models are widely used in the simulation of vaporous cavitation, especially in computational fluid dynamic simulation. In recent years, many efforts have been made to introduce the phase-change model [10], including the Rayleigh–Plesset model [11–13], to bearing analysis. From the physical mechanism perspective, however, cavitations in oil-film bearing are commonly not the vaporous cavitation form due to two reasons. One reason is the low vapor pressure of the lubricating oil used in the sliding bearing, which is always much lower than the measured pressure in the cavitation area [14]. For instance, the absolute vapor pressure of the lubricating oil ISO VG22 is approximately 3  10 6 Pa at 20  C and only 0.4 Pa even at temperatures of 100  C. The other reason is that cavitation ero- sion seldom occurs in the bearing, which indicates that vaporous cavitation is nonexistent in general. Developing a cavitation model based on its physical mechanism is a good initial step. In this paper, the cavitation form in the bear- ing is considered as gaseous cavitation, where the air is supplied from the emission of air dissolved in the oil, except in extreme situations where the loading is very heavy or varies abruptly, such as in high-frequency vibrations [14,15] and so on. However, a mature model for gaseous cavitation in oil-film bearings is still not available. Therefore, in this work, a new gaseous cavitation model based on air solubility is developed, and the gaseous cavita- tion mechanism is shown to predict and explain the cavitation phenomena that take place in the bearing. The rest of this paper is organized as follows. In Sec. 2, the governing Reynolds equation is used considering the possible 1 Corresponding author. Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 16, 2011; final manuscript received April 15, 2012; published online June 12, 2012. Assoc. Editor: C. Fred Higgs III. Journal of Tribology JULY 2012, Vol. 134 / 031701-1 Copyright V C 2012 by ASME Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 12/01/2014 Terms of Use: http://asme.org/terms