Tribological Optimization of Thrust Bearings Operated With Lubricants of Spatially Varying Viscosity

Abstract

In the present work, a computational optimization study of thrust bearings lubricated with spatially varying viscosity lubricants is presented, with the main goal of minimizing friction coefficient. In practice, spatial variation of viscosity could be achieved by utiliz ing electrorheological or magnetorheological fluids. The bearings are modeled as twodimensional (2D) channels, consisting of a smooth moving wall (rotor) and a parallel or inclined stationary wall (stator), which can be (i) smooth, (ii) partially textured with rec tangular dimples, and (iii) smooth and partially hydrophobic. The bearings are consid ered to be operated with an ideal lubricant that exhibits different values of viscosity in two distinct regions of the fluid domain: a high viscosity area is considered at the channel inflow, with the viscosity acquiring a reference (low) value farther downstream. The flow field is calculated from the numerical solution of the Navier-Stokes equations for 2D incompressible isothermal flow. The bearing geometry is defined parametrically. Three optimization problems are formulated, corresponding to: (I) a conventional smooth converging slider, (II) a parallel slider with artificial surface texturing at part of the stator surface, and (III) a parallel or converging slider with hydrophobic properties at part o f the stator surface. Here, the geometry parameters, as well as the increased viscos ity value and the corresponding application regime, form the problem design variables. Bearings are optimized for maximum load capacity and minimum friction coef ficient. Optimal solutions are compared against corresponding ones for operation with constant viscosity. It is demonstrated that, by using spatially varying viscosity, a substantial reduction of friction coefficient can be achieved, for all optimization problems considered. This decrease is shown to be a consequence of a sharp pressure rise in the high viscosity regime, resulting in a corresponding rise in load capacity, accompa nied by a less pronounced increase in wall shear stress, and thus in total friction force.

Optimization of Hydrostatic Thrust Bearing Using Enhanced Grey Wolf Optimizer

“…The studies conducted to improve the performance of hydrostatic bearings show that the most important feature expected from the bearings should be a good abrasion resistance [20][21][22][23][24][25]. The thrust bearings are expected to have such properties as low friction coefficient, high abrasion resistance, high loading capacity, good erosion resistance, good thermal conductivity and low thermal expansion values in their selection.…”

“…Therefore, the first three best solutions obtained during the algorithm are stored and the locations of other search agents (omegas) are updated according to the location of the best search agents (Eqs. (19)(20)(21)(22)(23)(24)(25) ( 1) . 3…”

Gas-Expanded Lubricants for Increased Energy Efficiency and Control in Rotating Machinery

“…Magnetic bearings are utilized in select applications as well, providing the benefits of both greater efficiency and rotordynamic control [20][21][22][23][24][25][26][27][28][29], though their use often comes at the expense of high energy consumption, limited load capacity, higher cost, and the requirement for backup bearing systems for energy-loss or control-loss emergency scenarios. Electro-rheological and magneto-rheological fluids have also been proposed as "smart" fluids that could be used to increase bearing performance, though these are still in the early stages of development due to extreme technological demands [30,31].…”

“…The bearing model employed in this study is a well-established TEHD analysis [76][77][78] that has also been previously used to model GEL performance in tilting pad journal bearings [31,36,79]. The model is based on the two-dimensional forms of the generalized Reynolds and energy equations, which enable the study of lubricant viscosity and its effects on operating temperature, power loss, eccentricity, and stiffness and damping behavior.…”