| Under high speed and super-high speed conditions, the oil film is easy to crack and becomes cavitation. The existence of cavitation has a great effect on the work characteristics of journal bearing which brings out more and more attention. The boundary of cavitation is the best important, the decision of rupture boundary and reformation boundary of oil film is nessary to keep bearing working in a desirable conditon. Based on this, the cavitation characteristics of a spiral oil wedge journal bearing have been investigated theoretically and experimentally with a view to design and application of high speed journal bearings.Firstly, based on the rupture boundary and reformation boundary of oil film which is satisfied with the flowrate balance, the common equation which integrates the oil film region and cavitation region is established, and deduced the formulas by means of finite differential method.Secondly, the rupture region shapes of oil film, rupture locations of oil film, reformation locations of oil film and rupture area of spiral oil wedge journal bearing are studied theoretically, And the influences of spiral angle of oil wedge, rotating speed and supply pressure on cavitation characteristics are investigated. The results show that spiral angle and eccentricity ratio have great influences on rupture location of oil film; the change of rotating speed and supply pressure has not an effect on rupture location; and rotating speed, supply pressure and eccentricity ratio have a great influenc on reformation location of oil film and rupture area of oil film.Thirdly, the original journal bearing experiment table is improved in order to observe the cavitation. The material of journal bearing is synthetic glass. Then takes some pictures of spiral oil wedge journal bearings under different rotating speeds and supply pressures and measures the oil flowrate of the journal bearings and outlet holes of spiral oil wedge journal bearing and temperature rise of the lubricant. Finally, obtains the relations of reformation location of oil film and rupture area of oil film with the rotating speed of the shaft and supply pressure and finds that rotating speed and supply pressure have not an effect on rupture location of oil film. And compared with common three wedge journal bearing in the experiment, and reveals the cavitation characteristic of each.The experimental fitting boundary is compared with JFO boundary and shows the rupture location of oil film under two boundarys is almost identical, the reformation location of one oil wedge is the same with experiment result and the reformation of the other has a great gap, the main reason is that two oil wedge locates the bottom of experiment table and has some errors in the measurement. The error between the theoretical result and the experimental result of rupture area of oil film is more less.Based on JFO boundary and experimental fitting boundary, the effects of the bearing configuration and work parameters on the bearing performances are researches and reveals unique characteristic of the bearing. The results show the configuration of oil wedge of spiral oil wedge journal bearing has a great influence on the static and dynamic performances, there are some errors between JFO boundary and experimental fitting boundary that are caused by measurement and fitting of boundary condition.Finally, thermohydrodynamic analysis of spiral oil wedge journal bearing is carried out. Based on the experiment, the lubricant flow in the cavitated region consists of two parts:narrow oil streamers extending over the gap and between the film rupture and reformation boundaries. There is a two-phase flow in the cavities region, it is assumed that a homogenous mixture of vapor and lubricant exists in the cavitated zone and the physical parameters are substituted with a mean physical properties.of two phase flow. In uncavitated part the physical parameters of lubricant is with oil. Using finite differetial method, the generalized Reynolds equation, energy equation of oil film and heat conduction equation of the bush are solved. Then the effects of spiral angle of oil wedge, supply pressure and supply oil temperature on the bush inner surface temperature distribution of spiral oil wedge journal bearing arc investigated. And the results indicate that spiral angle and supply oil temperature have a great effect on the bush inner surface temperature, but contrarily, supply pressure has a little effect.This work is supported by the National Basic Research Program of China(973 Program)(No.2009CB724404)... |
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