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

Abstract

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.

Numerical solution of dry friction in point contact using the unified Reynolds method combined with rarefied gas effect

“…Beginning with the input of initial parameters, the Hertzian contact pressure P old at level I is computed using the conjugate gradient method. An initial rigid film thickness H 0 is established, and the elastic deformation is determined using equation (14). Ultimately, the film thickness H is derived.…”

“…In this scenario, the theory of continuum mechanics fails. There are many studies on the numerical solution of the gas lubrication equation under a given film thickness, with representative work such as that on spiral-groove thrust microbearings. 11–14 For dry friction, the classic Reynolds equation with the continuum assumption is no longer valid because the Knudsen number K n of the air flow is larger than 0.001. The rarefaction effect must be considered.…”

Stability of orifice-compensated air bearing with rectangular shape considering air film thickness

“…4 There are two types of air bearings including the aerostatic bearings 5 and the aerodynamic bearings. 6 The aerostatic bearings are externally pressurized while the aerodynamic bearings are self-acting. According to different flow compensation units, the aerostatic bearings can be categorized into four types: the orifice-compensated air bearing, 7 the constant-compensated air bearing, the porous air bearing, 8 and the groove-compensated air bearing.…”

Integrated design and analysis of a high-precision aerostatic spindle for internal grinding machines and its implementation perspectives

“…In ultra-precision spindle systems, the spindle characteristics at various scales correspond to the machining errors at various scales of sub-micron shape error and nanoscale surface roughness. Research has focused on the influence of the air film geometry 1,2 and dimensional parameters 3,4 at the microscopic level as well as the air supply pressure 5 on essential bearing performance parameters: load capacity, stiffness and mass flow rate. 6,7 Chen et al 8 examined the major requirements in the design of the number and arrangement of the aerostatic bearings orifice for spindles operating at either low or high speeds.…”