Effect of surface roughness and deformation on Rayleigh step bearing under thin film lubrication

Abstract

Purpose The aim of this paper is to study the effect of deterministic roughness and small elastic deformation of surface on flow rates, load capacity and coefficient of friction in Rayleigh step bearing under thin film lubrication. Design/methodology/approach Reynolds equation, pressure-density relationship, pressure-viscosity relationship and film thickness equation are discretized using finite difference method. Progressive mesh densification (PMD) method is applied to solve the related equations iteratively. Findings The nature and shape of roughness play a significant role in pressure generation. It has been observed that square roughness dominates the pressure generation for all values of minimum film thickness. Deformation more than 100 nm in bounding surfaces influences the film formation and pressure distribution greatly. Divergent shapes of film thickness in step zone causes a delay of pressure growth and reduces the load capacity with decreasing film thickness. The optimum value of film thickness ratio and step ratios have been found out for the maximum load capacity and minimum coefficient of friction, which are notably influenced by elastic deformation of the surface. Practical implications It is expected that these findings will help in analysing the performance parameters of a Rayleigh step bearing under thin film lubrication more accurately. It will also help the designers, researchers and manufacturers of bearings. Originality/value Most of the previous studies have been limited to sinusoidal roughness and thick film lubrication in Rayleigh step bearing. Effect of small surface deformation due to generated pressure in thin film lubrication is significant, as it influences the performance parameters of the bearing. Different wave forms such as triangular, sawtooth, sinusoidal and square formed during finishing operations behaves differently in pressure generation. The analysis of combined effect of roughness and small surface deformation has been performed under thin film lubrication for Rayleigh step bearing using PMD as improved methods for direct iterative approach.

Thermo-elastohydrodynamic lubrication simulation of the Rayleigh step bearing using the progressive mesh densification method

“…Figure 8 showcases the non-dimensional load carrying capacity at different values of film thickness ratio with varying minimum film thickness. Under the EHL condition (as shown in Figure 8(a); Kumar et al 24 ), the load carrying capacity is slightly greater compared to that in the Thermo-EHL condition (as shown in Figure 8(b)) for all values of minimum film thickness. This is because the position of maximum pressure and the area under the no-pressure zone are affected by the generated temperature, as it tends to reduce the generated pressure and no-pressure zone (as discussed in Section 3.2) and finally the load carrying capacity.…”

“…Figure 10 shows the non-dimensional coefficient of friction for the EHL condition (as shown in Figure 10(a); Kumar et al 24 ) and the Thermo-EHL (as shown in Figure 10(b)) condition at different film thickness ratios. In both conditions the frictional coefficient is more for h 2 = 200 nm at a small value of k .…”

“…The optimum value of step ratio for maximum load capacity increases in the case of the Thermo-EHL condition compared with the EHL condition. Figure 10 shows the non-dimensional coefficient of friction for the EHL condition (as shown in Figure 10(a); Kumar et al 24 ) and the Thermo-EHL (as shown in Figure 10(b)) condition at different film thickness ratios. In both conditions the frictional coefficient is more for h 2 = 200nm at a small value of k. At a large value of k, the frictional coefficient for h 2 = 1000nm dominates under both conditions.…”

“…When the thickness of the film becomes thinner and thinner, the surface deformation becomes proportionate to film thickness under low load. Only a few researchers, such as Carl, 19 Hemingway, 20 Nakamura et al, 21 Yagi et al, 22,23 and Kumar et al, 24 have dealt with small surface deformation under thin film lubrication to date. Carl 19 suggested that the elastic deformation of surfaces under small pressure of 7 MPa cannot be ignored.…”

Recirculation Flow and Pressure Distributions in a Rayleigh Step Bearing

“…The Reynolds equation is confined to just the contact region, but the Navier-Stokes equations can be applied throughout the flow field [24,25]. In order to optimize Rayleigh step bearing design scientifically, it is beneficial to obtain detailed flow information of the whole lubricant flow field [26].…”