Li-Ming Chu

Effects of Non-Newtonian Rheology on Curved Circular Squeeze Films: the Rabinowitsch Fluid Model

On the ground of the non-Newtonian Rabinowitsch fluid model, the study of Newtonian squeeze film problems of curved circular plates [P. R. K. Murti, Trans. ASME 97, 650 (1975)] is extended in this paper. According to the results, higher load capacities and longer approaching times are obtained for the curved plates lubricated with dilatant fluids, but the pseudoplastic lubricants result in reversed trends. The influences of non-Newtonian dilatant and pseudoplastic properties on the squeeze film characteristics are further emphasized for curved circular plates operating under a smaller minimum film height and a larger curved shape parameter. Numerical results of the non-Newtonian load capacity are also provided for specific values of the curved shape parameter, the nonlinear parameter, and the minimum film height.

EHL of circular contacts lubricating with mixture of two lubricants

Purpose – The purpose of this paper is to analyze and discuss the coupled effects of surface roughness and flow rheology for a homogeneous mixture of Newtonian base oil and power law fluids on the performance of elastohydrodynamic lubrication (EHL) circular contact problems.Design/methodology/approach – The average flow model is adapted for the interaction of the flow rheology of lubricant and surface roughness. The average Reynolds type equation (ARTE) and the related flow factors (which describes the coupled effects of surface roughness and flow rheology of a mixture), the viscosity‐pressure and density‐pressure relations equations, the elastic deformation equation, and the force balance equation are then solved simultaneously. The multilevel multi‐integration algorithm and Gauss‐Seidel iteration method are utilized to calculate the film thickness and pressure distributions of the EHL circular contact problems effectively.Findings – The effects of volume fraction, flow index of power law fluid, and surf...

MAGNETO-HYDRODYNAMIC NON-NEWTONIAN CURVED CIRCULAR SQUEEZE FILMS

The squeeze film performances between curved circular plates lubricated with an electrically conducting non-Newtonian fluid in the presence of external magnetic fields are investigated in this paper. Based upon the magneto-hydrodynamic flow theory together with the Stokes microcontinuum theory, the magneto-hydrodynamic non-Newtonian Reynolds equation is derived and applied to predict the curved circular squeeze film behaviors. Comparing with the hydrodynamic Newtonian case, the squeeze film characteristics for curved circular plates are improved by the use of an electrically conducting non-Newtonian fluid in the presence of external magnetic fields. Numerical values of the load capacity and the approaching time are provided in Tables for engineering applications.

The effects of non-Newtonian rheology in the dynamic coefficients of wide slider bearings with a secant-shaped film profile

Purpose – The purpose of this paper is to investigate the effects of non-Newtonian rheology on the dynamic characteristics of a secant-shaped couple-stress lubricated slider bearing. Design/methodology/approach – By applying the linear dynamic theory to the film force equation, a closed-form solution of the stiffness and damping coefficients is obtained for the secant-shaped bearing taking into account the non-Newtonian effects of Stokes couple stress fluids. Findings – Comparing with the secant-shaped Newtonian-lubricant bearing, the effects of non-Newtonian couple stresses provide an apparent improvement in the dynamic stiffness and damping characteristics, especially for the secant-shaped slider bearing operating at lower squeezing-film heights and with larger non-Newtonian couple stress parameters. Originality/value – Comparing with those of the inclined plane-shaped non-Newtonian slider bearings, better dynamic stiffness and damping performances are provided for the secant-shaped non-Newtonian slider...

Effects of non‐Newtonian Rabinowitsch fluids in wide parallel rectangular squeeze‐film plates

Purpose – In the present paper, the authors aim to analyze the non‐Newtonian effects of Rabinowitsch fluids on the squeeze film performances between wide parallel rectangular plates.Design/methodology/approach – Based on the cubic‐stress equation model, a nonlinear squeeze‐film Reynolds‐type equation has been derived. By using a small perturbation method, a closed‐form solution of the squeeze film characteristics is derived for the parallel plates considering the non‐Newtonian effects of cubic stresses.Findings – Comparing with the Newtonian‐lubricant parallel plates, the effects of non‐Newtonian cubic‐stress flow rheology provide significant influences upon the squeeze film characteristics.Originality/value – It is shown that the non‐Newtonian pseudoplastic behavior reduces the load capacity and the response time; however, the effects of non‐Newtonian dilatant lubricant provide an increase in the load‐carrying capacity and therefore lengthen the response time of parallel squeeze‐film plates.

Squeeze Film Problems of Long Partial Journal Bearings for Non-Newtonian Couple Stress Fluids with Pressure-Dependent Viscosity

Abstract According to the experimental work of C. Barus in Am. J. Sci. 45, 87 (1893) [1], the dependency of liquid viscosity on pressure is exponential. Therefore, we extend the study of squeeze film problems of long partial journal bearings for Stokes non-Newtonian couple stress fluids by considering the pressure-dependent viscosity in the present paper. Through a small perturbation technique, we derive a first-order closed-form solution for the film pressure, the load capacity, and the response time of partial-bearing squeeze films. It is also found that the non-Newtonian couple-stress partial bearings with pressure-dependent viscosity provide better squeeze-film characteristics than those of the bearing with constant-viscosity situation.

Effects of Anisotropic Slip on the Elastohydrodynamic Lubrication of Circular Contacts

By coupling the equations of the modified Reynolds equation with the anisotropic slip effect, the piezoviscosity and piezodensity relations, the elasticity deformation equation, and the load equilibrium equation are solved simultaneously using the finite element method (FEM) for the elastohydrodynamic lubrication (EHL) of circular contact problems under constant load conditions. Results show that the film thickness is more sensitive to the slip length in a sliding direction (x-direction) than to the slip length in a transverse direction (y-direction). A slip in the y-direction concentrates the pressure toward the center region, and the film collects toward the central region and possesses a deeper dimple. The central pressure and coefficient of friction (COF) increase as the slip length in the y-direction increases. On the contrary, the central pressure and COF decrease as the slip length in the x-direction increases. Detailed results and animations for film thicknesses and pressure distributions are available under the “Supplemental Data” tab for this paper on the ASME Digital Collection.

Elastohydrodynamic lubrication of circular contacts at pure squeeze motion with micropolar lubricants

Purpose This paper aims to explore pure squeeze elastohydrodynamic lubrication (EHL) motion of circular contacts with micropolar lubricants under constant load. The proposed model can reasonably calculate the pressure distributions, film thicknesses and normal squeeze velocities during the pure squeeze process. Design/methodology/approach The transient modified Reynolds equation is derived in polar coordinates using micropolar fluids theory. The finite difference method and the Gauss–Seidel iteration method are used to solve the transient modified Reynolds equation, the elasticity deformation equation, load balance equation and lubricant rheology equations simultaneously. Findings The simulation results reveal that the effect of the micropolar lubricant is equivalent to enhancing the lubricant viscosity. As the film thickness is enlarged, the central pressure and film thickness for micropolar lubricants are larger than those of Newtonian fluids under the same load in the elastic deformation stage. The greater the coupling parameter (N), the greater the maximum central pressure. However, the smaller the characteristic length (L), the greater the maximum central pressure. The time needed to achieve maximum central pressure increases with increasing N and L. Originality/value A numerical method for general applications was developed to investigate the effects of the micropolar lubricants at pure squeeze EHL motion of circular contacts under constant load.

Effects of Surface Roughness and Flow Rheology on the EHL of Circular Contacts with Power-law Fluid

The coupled effects of surface roughness and flow rheology on the Elastohydrodynamic lubrication (EHL) circular contact problems are analyzed and discussed. The average flow model is adapted for the interaction of the flow rheology of lubricant and surface roughness. The averaged Reynolds type equation, the rheology equations, the elastic deformation equation, and the force balance equation are solved simultaneously. The multilevel multi-integration (MLMI) algorithm and Gauss-Seidel iteration method are utilized to calculate the film thickness and pressure distributions. The effects of flow index, Peklenik number, and standard deviation of composite surface roughness on the film thickness and pressure distributions are discussed. The results show that the transverse type roughness and standard deviation of composite roughness enhance the pressure and film thickness in the central contact region. Moreover, the greater the flow index is, the greater the pressure distribution is in the central contact region, and the greater the film thickness is in all regions.

Effect of Surface Roughness on Pure Squeeze EHL Motion of Circular Contacts

Purpose – The purpose of this paper is to explore the pure squeeze elastohydrodynamic lubrication motion of circular contacts with surface roughness under constant load conditions. The proposed model can reasonably calculate the effects of surface roughness on the transient pressure profiles, film shapes, and normal squeeze velocities during the pure squeeze process.Design/methodology/approach – Based on Christensens stochastic theory, the transient modified Reynolds equation is derived in polar coordinates to consider the effects of surface roughness. The finite difference method and the Gauss‐Seidel iteration method are used to solve the transient modified Reynolds equation, the elasticity deformation equation, load balance equation, and lubricant rheology equations simultaneously.Findings – The simulation results reveal that the circular type roughness possesses storage oil capacity. Comparatively, the radial type roughness possesses leak oil capacity. Therefore, the film thickness is found with circu...