A mixed thermal elastohydrodynamic lubrication model of rotary lip seal

Rotary lip seal is used in various applications where the rotation shaft needs to be sealed, such as hydraulic pumps, fuel pumps, camshafts, crankshafts, and so on. Many thermal elastohydrodynamic lubrication models of rotary lip seal have been introduced, and most of these models neglect the asperity contact. This article proposes a mixed thermal elastohydrodynamic lubrication model of rotary lip seal, in which the microstructure of sealing lip surface, influence of temperature on fluid viscosity, and deformation of lip surface, as well as the asperity contact, are taken into consideration. Simulation study is carried out, and the results show that the asperity contact should not be neglected for analyzing the sealing performance of the rotary lip seal. The influence of speed on the sealing performance is also analyzed based on the proposed model.

On the multiple solutions of coating and rimming flows on rotating cylinders

We consider steady solutions of the Stokes equations for the flow of a film of fluid on the outer or inner surface of a cylinder that rotates with its axis perpendicular to the direction of gravity. We find that previously unobserved stable and unstable steady solutions coexist over an intermediate range of rotation rates for sufficiently high values of the Bond number (ratio of gravitational forces relative to surface tension). Furthermore, we compare the results of the Stokes calculations to the classic lubrication models of Pukhnachev (J. Appl. Mech. Tech. Phys., vol 18, 1977, pp. 344–351) and Reisfeld & Bankoff (J. Fluid Mech., vol. 236, 1992, pp. 167–196); an extended lubrication model of Benilov & O’Brien (Phys. Fluids, vol. 17, 2005, 052106) and Evans et al. (Phys. Fluids, vol. 16, 2004, pp. 2742–2756); and a new lubrication approximation formulated using gradient dynamics. We quantify the range of validity of each model and confirm that the gradient-dynamics model is most accurate over the widest range of parameters, but that the new steady solutions are not captured using any of the simplified models because they contain features that can only be described by the full Stokes equations.

Conservation Laws of Some Physical Models via Symbolic Package GeM

We study the conservation laws of evolution equation, lubrication models, sinh-Poisson equation, Kaup-Kupershmidt equation, and modified Sawada-Kotera equation. The symbolic software GeM (Cheviakov (2007) and (2010)) is used to derive the multipliers and conservation law fluxes. Software GeM is Maple-based package, and it computes conservation laws by direct method and first homotopy and second homotopy formulas.

Modeling EHL of Rough Piston Skirts Using Different Viscosity-Grade Lubricants in Initial Engine Startup

An engine lubricant plays a significant role in preventing adhesive wear of the rough interacting surfaces of the piston skirts and the cylinder liner. A fully established elastohydrodynamic lubricating (EHL) film, appropriate viscosity oil and the fairly rough interacting surfaces prevent wear during normal engine operation. The absence of an EHL film and inappropriate viscosity lubricant fail to minimize wear in the initial engine startup. This work considers a fairly viscous Newtonian engine lubricant to model the rough piston skirts hydrodynamic and EHL in the initial engine start up. The isotropic surfaces of the skirts and the cylinder liner having different roughness amplitudes are considered in the basic lubrication models. The flow factors are introduced in the 2-D average Reynolds equation, which is solved numerically to generate the hydrodynamic pressures. The inverse solution technique is used to develop the basic EHL model of the rough surfaces. The secondary piston dynamics and the contact geometry of interacting surfaces are incorporated in the basic lubrication models. The profiles of the piston eccentricities, secondary velocities, film thicknesses and pressures are generated as the function of 720 degrees crank rotation cycle. The study is extended to develop the lubrication models for the low and high viscosity grade engine lubricants separately. The simulation results are analyzed and compared with those of the basic lubrication model. The results show that the different lubricant viscosities alter the secondary displacements of the sliding piston and affect the lubrication of the rough interacting surfaces. The comparative analysis leads to optimize the use of appropriate viscosity-grade engine lubricant for a few low speed initial engine startup cycles.

Analysis of Piston Ring Lubrication with Different Lubricant Supply

In this paper fully flooded and starved lubrication models considering surface roughness are developed for the piston ring and cylinder bore lubrication. The effect of oil available in the inlet region of a top ring is studied by comparing predicted oil film thickness, asperity contact friction and power loss under different oil supply conditions. The simulation results show that the proper oil supply is important in controlling the piston ring frictional power loss. The influences of lubricant viscosity and composite roughness on frictional power loss of piston ring are also discussed.

Analytical Solution to the Hydrodynamic Lubrication of Fan-Shaped Thrust Step Bearings

Step bearings are frequently used in industries for better load capacities. Analytical solutions to the Rayleigh step bearing and a rectangular slider with a finite width are available in literature, but none for a fan-shaped thrust step bearing. This study starts with a known solution to the Laplace equation in a cylindrical coordinate system, which is in the form of an infinite summation. A set of analytical solutions to pressure, load capacity, flow rate, and torque loss is derived in this paper for hydrodynamic lubrication problems encountered in the fan-shaped step bearing. These analytical solutions are compared with those for the rectangular slider and the Rayleigh step bearing to reveal relationships among them. When the inner radius becomes smaller, the load capacity increases, almost linearly in a certain region. The effects of inner radius, step height, and step location on pressure distribution and load capacity are studied in general and under a specific set of bearing geometry as an example. The presented solutions can be useful for designers to maximize bearing performance as well as for researchers to benchmark numerical lubrication models.

Hydrodynamic Pressure of Thrust Step Bearings

Step bearings are frequently used in industry for better load capacity. Analytical solutions to the Rayleigh step bearing and a rectangular slider with a finite width are available in literature, but none for a fan-shaped thrust step bearing. This study starts with a known solution to the Laplace equation in a cylindrical coordinate system, which is in the form of infinite summation. An analytical solution to pressure is derived in this paper for hydrodynamic lubrication problems encountered in the fan-shaped step bearing. The presented solutions can be useful for designers to maximize bearing performance as well as for researchers to benchmark numerical lubrication models.