Effect of texture geometry on the performance of noncircular aerodynamic journal bearings

Today, considerable uses of aerodynamic journal bearings have attracted the attention of many researchers in the field of tribology. Therefore, the theoretical and experimental analysis of their performance has been the subject of many researches. Growing application of the gas journal bearings is due to their capability in various engineering fields such as instrumentation and high-speed machines like spindles, small-scale turbomachines, and precision gyroscopes, dental milling machines, and many other rotor-bearing systems. Upgrading the performance of gas bearings by changing their geometry or using new compressible lubricants has always been one of the suggestions proposed by the tribology researchers. Recently, the development of new technologies such as laser milling and lithography increased the possibility of creating textured surfaces as a way to improve the performance of journal bearings. So, in this study, the effects of texture geometry on the steady-state performance of two-lobe noncircular aerodynamic journal bearings are presented. For this purpose, the governing Reynolds equation of hydrodynamic gas lubrication is analyzed by finite element method according to the changes of the lubricant film thickness in presence of the cubical, cylindrical, and ellipsoidal surface textures. Results show that the creation of textures on the lower lobe compared to the upper lobe or the whole surface is more effective on the performance of two-lobe aerodynamic bearings. Also, increasing both the dimple depth and the amount of bearings noncircularity, especially at shallow texture depth, cause more significant changes in the lubricant film pressure distribution and the bearing performance parameters such as load-carrying capacity, attitude angle, and frictional power loss. Further, it is obvious that the creation of cubical, cylindrical and ellipsoidal textures especially at shallow depth with an increase in the noncircularity of bearings’ geometry have a higher impact on the steady-state performance of the studied rotor-bearing system, respectively.

Prediction on Flow and Thermal Characteristics of Ultrathin Lubricant Film of Hydrodynamic Journal Bearing

This paper focuses on the flow and thermal characteristics of the lubricant film in the micro clearance of a hydrodynamic journal bearing (HJB) at high rotating speed. A thermohydrodynamic (THD) method consists of the Reynolds equation coupled with energy and viscosity-temperature equation with considering the cavitation is put forward. The 3D surface diagrams of the lubricant film thickness, pressure, temperature, liquid mass fraction, flow rate and heat dissipation distributions under different geometric, operating, slip and no-slip boundary conditions are systemically exhibited and analyzed. The results show that with the rise of eccentricity or length diameter ratio, the maximum peaks of pressure, temperature and heat dissipation are rapidly increased, the cavitation is aggravated, and the flow rate is accelerated in different extent. As the bearing speed accelerating, the maximum peak of temperature is strongly increased, whereas, the distinction between peaks of flow rate and heat dissipation is magnified and reduced, respectively. It provides a fruitful inside view of the inner flow and thermal characterizations of HJB for further understanding its flow-thermal interaction mechanisms and offers theoretical support for improving its working performance.

Effect of Lubricant Starvation on the Tribo-Dynamic Behavior of Linear Roller Guideway

This paper presents an experimentally validated numerical approach linear roller guideways considering coupled vertical and horizontal (feed) motions and taking into account lubricant starvation. The inlet starvation is considered by incorporating potential flow method. Results show that starvation has pronounced effect on the lubricant film thickness, friction, and applied load on contact by up to 32%. Localised pressure values may vary by up to 100%. The severity of starvation effect is frequency dependent. It is also revealed that the starvation effect can be controlled by the amount of preload on linear guideway.