Lubrication Model And Numerical Computation Of Electrorheological Journal Bearings

Electrorheological (ER) fluid is a new kind of smart materials, under applied electric field its rheologic behavior can be dramatically changed, even into solid. ER effect is reversible with fast response and low dissipation. The prospect of ER application is very broad and the researches of ER fluid have more and more attentions.In the present thesis, theoretical analysis and numerical study of the lubrication performance for ER journal bearings are presented. A general Reynolds equation based on ER fluid model is obtained, which can be easily extended to other non-Newtonian fluids and this equation can provide theoretical basis for the hydrodynamic analysis of ER journal bearings.For the case of static loaded ER journal bearings, the influence of ER effects on the lubrication performance are studied under various radius clearances, eccentricity ratios and shear rates. The numerical results show that: with the enhancement of ER effects, the bearing capacity is obviously increased; the increase magnitude is larger when small radius clearances and large eccentricity ratios; at low shear rates, the influence of ER effects on the lubrication performance of journal bearings are more obvious.For the case of dynamically loaded ER journal bearings, the effects of ER fluids on the lubrication performance are numerically studied by simultaneously solving the Reynolds equation and the journal motion equation. It is shown that: with the enhancement of ER effects, the pressure and the thickness of lubricant film are obviously increased, while the friction coefficient and force are increased, the leak flow is reduced.For the specific yield surface problem of Bingham fluid, the yield characteristics of Bingham and ER fluid flow in journal bearings with infinite length are analyzed. It is shown that: at the position of maximum bearing clearance, the non-yield region is attached to bushing, while at the position ofminimum clearance, the non-yield region is attached to journal. With the yield stress increase, the yield surface moves to enlarge the non-yield region, when yield stress reach to a specific value, the yield stress saturation occurs. For the kind of ER devices with high shear rates, such as journal bearings, the apparent viscosity could be changed very little with applied electric field. It is proposed in the present thesis that: the movement of yield surface is the important factor in the response of ER devices to applied electric field.