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The effect of surface texture and roughness on shear and pressure forces in tribological applications in the lubrication regime is analyzed by means of lattice-Boltzmann simulations that take the geometry of real surface elements into account. Topographic data on representative surface structures are obtained with high spatial resolution with the application of an optical interference technique. The three-dimensional velocity field past these surfaces is computed for laminar flow of Newtonian fluids in the continuum regime. Subsequently, pressure and shear flow factors are obtained by evaluating the velocity field in accordance with the extended Reynolds equation of Patir and Cheng (1978, ASME J. Tribol., 100, pp. 12-17). The approach allows an efficient determination of the hydrodynamic characteristics of microstructured surfaces in lubrication. Especially, the influence of anisotropy of surface texture on the hydrodynamic load capacity and friction is determined. The numerical method used in the present work is verified for a simplified model configuration, the flow past a channel with sinusoidal walls. The results obtained indicate that full numerical simulations should be used to accurately and efficiently compute the characteristic properties of film flows past rough surfaces and may therefore contribute to a better understanding and prediction of tribological problems. [DOI: 10.1115/1.2736452] Keywords: hydrodynamic lubrication, surface roughness, lattice-Boltzmann simulation, Reynolds equation, flow factors

Starved lubrication occurs intentionally or unconsciously in many journal bearing applications. However, the determination of its concrete distribution in a journal bearing is rather complex as the different lube oil feed grooves interact with each other due to their connection by the lubricant flow along the pad surfaces and the periodic geometric property of the entire bearing. A robust numerical procedure to determine the lube oil distribution between the different feed grooves in a starved lubricated fixed-pad journal bearing is presented as an extension to Elrod's cavitation algorithm. The enhanced algorithm partly integrates flow rate boundary conditions into the linear system of equations for the solution of Reynolds equation and the transport equation. A strategy to couple these flow rate boundary conditions with the iterative procedure to determine the binary cavitation index is proposed. In particular, the algorithm enables an appropriate modeling of lube oil grooves with locked oil supply including the consideration of groove-specific dissipation or design features like bleed notches. The novel algorithm is implemented as a submodule of a thermo-elasto-hydrodynamic bearing code and validated with test data for a high-speed two-lobe bearing with embedded arc. Furthermore, a comprehensive parametric study provides an insight on the robustness of the implemented numeric procedure. Results, current limitations, and possible extensions to the algorithm are discussed. [ABSTRACT FROM AUTHOR]

Flooded lubrication of tilting-pad journal bearings provides safe and robust operation for many applications due to a completely filled gap at the leading edge of each pad. Direct lubrication by leading edge grooves (LEG) located on the pads represents an alternative to restrictive end seals to ensure these conditions at the entrance to the convergent lubricant film. A theoretical model is presented that describes the specific influences of LEG design on operating characteristics. First, in contrast to conventional tilting-pad journal bearing designs, the LEG is a self-contained lube oil pocket, which is generally connected to an outer annular oil supply channel. Consequently, each LEG can feature a specific speed and load-dependent effective pocket pressure, which influences the pad tilting angle. Second, the thermal inlet mixing model must consider the specific flow conditions depending on the main flow direction within the film as well as the one between outer annular channel and pocket. The novel LEG model is integrated into a comprehensive bearing code and validated with test from a high performance test rig for a four tilting-pad bearing in load between pivot orientations. Within the investigated operating range good agreement between theoretical and experimental data is achieved if all boundary conditions are accurately considered. Additionally, the impact of single simplifications within the model is studied and evaluated. Finally, the test data are compared to results from the same test bearing with modified lubricant oil supply conditions in order to identify specific properties of LEG design. [ABSTRACT FROM AUTHOR]