Effects of Surface Roughness and Supply Inertia on Steady Performance of Hydrostatic Thrust Bearings Lubricated with Non-Newtonian Fluids

The objective of present theoretical analysis is to study the combined effects of surface roughness and fluid inertia (including the inertia of the fluid in the supply region) on the steady performance of stepped circular hydrostatic thrust bearings lubricated with non-Newtonian pseudoplastic fluids using Rabinowitsch stress-strain model. To account for the effects of surface roughness, the classical Christensen theory of rough surface has been taken. Analytic expressions for film pressure in bearing regions have been established for radial and circumferential patterns of roughness. Numerical results for film pressure, load carrying capacity and lubricant flow rate has been plotted and analysed. Due to surface roughness and fluid inertia in overall regions, significant improvement in performance properties have been observed.

Measurements to Quantify the Effect of a Reduced Flow Rate On the Performance of a Tilting Pad Journal Bearing (LBP) with Flooded Ends

Operation of tilting pad journal bearings (TPJBs) with a reduced flow improves system energy efficiency by reducing drag power losses, albeit the temperature rise in both the bearing pads and the lubricating oil become a concern. This paper presents measurements of the static and dynamic load performance of a flooded ends TPJB with flowrates ranging from 150% to ~5% of a nominal supply condition. The test bearing is a four-pad, 102 mm diameter, center pivot, with single orifice feeds, and configured with end seals. Experiments include operation at two shaft speeds = 6 krpm and 12 krpm and under three specific loads = 0.345 MPa, 1.03 MPa and 2.07 MPa applied in between pads (LBP). The measurements show the bearing drag power loss decreases by nearly 20% when flow rate drops to 50% of nominal. However, halving the flow produces a raise in pad subsurface temperatures, ~7 °C for operation at 12 krpm. Flow reduction below 50% results in substantial power savings; however, it also produces too hot pad temperatures that approach a known limit for Babbitt material safe operation. Damping coefficients decrease by ~30% as the flow rate decreases from 150% to just a few % of nominal flow. The experimental results are first to quantify operation of a TPJB supplied with minute amounts of lubricant flow. A test with a very low flow rate at ~2% of nominal and under a light load produced the emergence of a broadband subsynchronous vibration frequency, albeit with very small amplitude.

Influence of turbulent cavitating flow on performance characteristics of spiral groove liquid film seal

Spiral groove liquid film seal is expected to be the prime candidate for application to high-speed liquid-oxygen turbopumps, and the lubricant flow between the sealing faces is turbulent due to the liquid-oxygen properties and the working conditions. Based on the Ng–Pan model and mass-conserving algorithm, the modified dynamic Reynolds equation considering flow regime and cavitation is obtained, which is solved by the finite-difference method. The effects of flow regime and cavitation on the performance of spiral groove liquid film seal are analyzed. The results indicate that the balanced film thickness and opening force increase due to the turbulent flow. The cavitation ratio increases in the laminar–turbulent transition region, which reduces the opening force and liquid film stiffness.

Cavitation between cylinder-liner and piston-ring in a new designed optical IC engine

A new engine block with optical access has been designed and manufactured capable of running up to 3000 r/min with the same specification as the unmodified engine. The optical window allowed access to the full length of the liner over a width of 25 mm to investigate the lubricant flow and cavitation at contact point between the rings and cylinder-liner. In addition, it allowed good access into the combustion chamber to allow charged flow, spray and combustion visualisation and measurements using different optical methods. New custom engine management system with build in LabView allowed for the precise full control of the engine. The design of the new optical engine was a great success in producing high quality images of lubricant flow, cavitation formation and development at contact point at different engine speeds ranging from 208 to 3000 r/min and lubricant temperatures (30°C–70°C) using a high-speed camera. The results under motorised operation confirmed that there was no cavitation at contact points during the intake/exhaust strokes due to low in-cylinder presure, while during compression/expansion strokes, with high in-cylinder pressure, considerable cavities were observed, in particular, during the compression stroke. Lubricant temperatures had the effect of promoting cavities both in their intensity and covered ring area up to 50°C as expected. Beyond that, although the cavitation intensity increases further with temperature, its area reduces due to possible collapse of the cavitating bubbles at higher temperature. The change of engine speed from 208 to 800 r/min increased cavitating area considerably by 52% of the ring area and was further increased by 19% at 1000 r/min. After that, the results showed very small increase in cavitation area (1.3% at 2000 r/min) with similar intensity and distribution across the ring.

THE INFLUENCE OF KINEMATIC CONDITION AND LUBRICANT PROPERTIES ON FRICTION IN COMPLEX SLIDE–ROLL MOTION

The paper presents the results of preliminary studies into the influence of selected lubricants (greases) and the variable temperature of the friction joint on the value of friction during complex slide-roll motion. The experiment was carried out for three different types of lubricants: bentonite grease (Benterm 2), lithium grease (GREASEN ŁT4S2), and calcium grease with the addition of graphite (GREASEN GRAFIT) at different temperatures. Tribological investigations were carried out in a roller-plate system at a wide range of plate dislocation velocities and at a constant slip rate; rheological investigations consisted in determining the changes in shear stress as a function of shear time at constant average shear velocity of 50 mm/s. The results showed a significant influence of kinematic conditions on the value of friction. Four different cases of lubricant flow during friction were identified. The least resistance to motion was found when the lubricant was applied in the same direction along the surface of the roller and plate. It has been shown that the greatest influence of the kinematics of working elements on friction occurs at low temperatures, i.e. at -10°C. This phenomenon is closely related to the rheological properties of the lubricant. It was also found that the lubricant thickened with bentonite is the most susceptible to kinematic changes of the friction joint.

On the Relation between Friction Increase and Grease Thickener Entraining on a Border of Mixed EHL Lubrication

This paper deals with an experimental study of film thickness and friction of commercial-grade grease and its base oil in a highly loaded contact. In-situ measurements were conducted for two surface textures on a ball-on-disc optical tribometer at the border of mixed lubrication. At high speeds, the film thickness and the friction of grease correspond with the base oil, while, the thickener enters the contact area and locally affects the film thickness and friction at low speeds. It was found out that the thickener starts to enter the contact area approximately at the same speed when the base oil friction increases on Stribeck curve but without direct solid to solid contact. It indicates that both effects can have the same origin. Change of lubricant flow in contact inlet area was discussed as a possible explanation.

Dynamic and stability performance improvement of the hydrodynamic bearing by using triangular-shaped textures

In the present study, the effect of triangular shape textured on the bearing dynamic and stability performance has been investigated. The triangular-shaped texture having variation in their depth size, number of textures, and location has been used in the study to find the stiffness, damping, and stability parameters and compared with un-textured bearing. The pressure and fluid-film thickness in the lubricant flow domain having characteristics of Newtonian and isothermal and which is governed with Reynold's equation have been computed by discretizing the domain into four-nodded quadrilateral isoparametric by using finite element method. Four different cases of texture distribution on the bearing surface have been studied. The study has been carried out considering the bearing operation only under average eccentricity ratios of 0.6. From obtained results, it is found that the value of direct stiffness coefficient and threshold speed is found maximum at lower texture depth and the direct damping coefficient is found maximum at higher value of texture depth corresponding to different texture distribution on the bearing surface. The optimum triangular-shaped textured parameters have been also finalized to get maximum dynamic performance and stability, which may be expected to be valuable for bearing designers. For the purpose of a better insight into the stability aspect of the optimal textured journal bearing, the journal center trajectories are also drawn and compared with un-textured bearing.