Hydrodynamic fluctuation-induced forces in confined fluids

Thermal hydrodynamic fluctuations in a classical, compressible, viscous fluid film give rise to fluctuation-induced forces between the no-slip fluid boundaries, whose average value is zero but their correlators are finite and represent a “secondary Casimir effect” in the hydrodynamic context.

Surface Wave on a Viscous Fluid Film down an Inclined Uneven Wall

The paper is devoted to a theoretical study of nonlinear wave on a free-surface thin film down an inclined uneven plane. The problem is quite different from that of a viscous films flow along a smooth surface. Thus nondimensional variables are introduced in two ways according to the different relationship of the shallow water parameter and the topography parameter. Further, the zero-order and first-order stream function are derivated on the basis of perturbation method. Finally, the equations which govern the surface height of surface wave on a viscous fluid film down an inclined uneven wall are obtained.

Partial Elastomer Texturing in Soft Elasto Hydrodynamic Lubrication

A dimensionless theoretical model of Soft Elasto Hydrodynamic Lubrication (SEHL) between partially textured elastomer and rigid counterpart is developed. The model consists of a soft elastomer with partial Laser Surface Texturing (LST) and an absolutely rigid and smooth counterpart moving relatively to each other in the presence of viscous lubricant. The elastomer surface is partially textured at its leading edge in the form of spherical micro-dimples. The pressure distribution in the fluid film and the elastic deformations of the elastomer are obtained from a simultaneous solution of the Reynolds equation and the equation of linear elasticity, respectively. Friction force and load carrying capacity are evaluated by integration of the shear stress and pressure fields in the viscous fluid film, respectively. The main goal of the present work is to study the potential of the elastomer partial LST in SEHL to friction reduction.

Low Friction and High Load Support Capacity of Slider Bearing With a Mixed Slip Surface

The classical Reynolds theory reveals that a converging gap is the first necessary condition to generate a hydrodynamic pressure in a viscous fluid film confined between two solid surfaces with a relative sliding/rolling motion. For hundreds of years, the classical lubrication mechanics has been based on the frame of the Reynolds theory with no slip assumption. Recent studies show that a large boundary slip occurs on an ultrahydrophobic surface, which results in a very small friction drag. Unfortunately, such a slip surface also produces a small hydrodynamic pressure in a fluid film between two solid surfaces. This paper studies the lubrication behavior of infinite width slider bearings involving a mixed slip surface (MSS). The results of the study indicate that any geometrical wedges (gaps), i.e., a convergent wedge, a parallel gap, and even a divergent wedge, can generate hydrodynamic pressure in an infinite slider bearing with a mixed slip surface. It is found that with an MSS, the maximum fluid load support capacity occurs at a slightly divergent wedge (roughly parallel sliding gap) for an infinite width slider bearing, but not at a converging gap as what the classical Reynolds theory predicts. Surface optimization of a parallel sliding gap with a slip surface can double the hydrodynamic load support and reduce the friction drag by half of what the Reynolds theory predicts for an optimal wedge of a traditional slider bearing.

Improving Tribological Performance of Piston Rings by Partial Surface Texturing

An analytical model is developed to study the potential use of partial laser surface texturing (LST) for reducing the friction between a piston ring and cylinder liner. The hydrodynamic pressure distribution and the time-dependent clearance between the piston ring and cylinder liner are obtained from a simultaneous solution of the Reynolds equation and the ring equation of motion in the radial direction. The time behavior of the friction force is calculated from the shear stresses in the viscous fluid film and the time-dependent clearance. An intensive parametric investigation is performed to identify the main parameters of the problem. The optimum LST parameters such as dimples depth, texture area density, and textured portion of the nominal contact surface of the piston ring are evaluated.