Hydrodynamic calculation of wedge-shaped system «slider-guide» operating on compressible lubricant in presence of melt on surface of guide

In the article on the basis of the equation of motion of the compressible lubricant for the «thin layer», continuity, state, and the equation describing the profile of the molten contour taking into account the formula of mechanical energy dissipation the asymptotic and self-similar solution is found for the extreme (when the speed tends to infinity) and non-extreme case. As a result of solving the problem, a refined mathematical calculation model of a wedgeshaped sliding support with a low-melting metal coating on a movable contact surface is obtained, which compensates for an emergency lack of lubricant and provides a stable hydrodynamic lubrication mode

A Compressible Thermohydrodynamic Analysis of Journal Bearings Lubricated With Supercritical CO2

In this study, a compressible thermohydrodynamic (THD) model was developed to examine the flow dynamics of a journal bearing lubricated with supercritical carbon dioxide (sCO2). This model employed a general form of the Reynolds equation governing compressible lubricant flows with a well-known analytical equation of state, and a viscosity model that depends on both pressure and temperature. In order to verify the model, we first compared the results of this compressible Reynolds equation to the full Navier-Stokes solutions. The accuracy of the model was found to be reasonable when the operating condition is sufficiently far from the thermodynamic critical point. Additionally, the numerical solution suggests that different temperature boundary conditions give slight different results due to the small variations of density and temperature across the gap. Finally, the general approach presented in this study introduces a new single parameter — effective bulk modulus that characterize both the frictional and thermodynamic fluid response. The model developed in this study can provide guidance for further studies of CO2-lubricated bearings operating in the full supercritical regime.

A direct numerical approach to compute the nonlinear rotordynamic coefficient of the noncircular gas journal bearing

Gas bearings are extensively used in several industrial applications to support the rotating load at high speed due to its favorable characteristics. The numerical computation of the gas film damping and stiffness coefficients is a difficult task due to nonlinearity in the Reynolds equation for compressible lubricant. In the present work, a numerical method based on the finite element method is developed for the direct computation of gas film damping and stiffness coefficients. In this method, a double partial differential equation approach has been used to compute the dynamic characteristics. Further, the numerical results presented shows that the bearing ellipticity ratio significantly affects the nonlinear trajectory of the journal.

A Waved Journal Bearing Concept-Evaluating Steady-State and Dynamic Performance With a Potential Active Control Alternative

Analysis of the waved journal bearing concept featuring a waved inner bearing diameter for use with a compressible lubricant (gas) is presented. The performance of generic waved bearings having either three or four waves is predicted for air lubricated bearings. Steady-state performance is discussed in terms of bearing load capacity, while the dynamic performance is discussed in terms of fluid film stability and dynamic coefficients. It was found that the bearing wave amplitude has an important influence on both steady-state and dynamic performance of the waved journal bearing. For a fixed eccentricity ratio, the bearing steady-state load capacity and direct dynamic stiffness coefficient increase as the wave amplitude increases. Also, the waved bearing becomes more stable as the wave amplitude increases. In addition, increasing the number of waves (e.g., four waves instead of three waves) reduces the waved bearing’s sensitivity to the direction of the applied load relative to the wave. However, the range in which the bearing performance can be varied decreases as the number of waves increases. Therefore, both the number and the amplitude of the waves must be properly selected to optimize the waved bearing design for a specific application. Another possibility is to use the waved bearing to actively control the rotor-bearing system dynamic coefficients via actively controlling the wave amplitude.

Extension of the Patir-Cheng Flow Simulation of a Rough Surface Bearing to a Compressible Lubricant

It is shown that the average Reynolds equation for rough surfaces using an incompressible lubricant derived by Patir and Cheng (1)§ can be used for a compressible lubricant if the surface structures of both surfaces are the same. The average Reynolds equation is applied to an infinitely long gas journal bearing to find the hydrodynamic load capacity. The effect of the roughness parameter and the surface pattern parameter on the hydrodynamic load is also investigated.

A Theoretical Analysis of a Compliant Shell Air Bearing

A mathematical analysis of a class of compliant journal bearings operating with a compressible lubricant is presented. Finite element methods are used to obtain approximate solutions, and results for the rigid case are compared to those obtained by finite difference methods. Results for the case in which the compliant bearing component is a shell show that the steady-state performance can be radically different from that predicted by the rigid bearing assumption. These differences may explain the antiwhirl characteristics exhibited by this type of bearing.

Dynamic Characteristics of Externally Pressurized Rectangular Porous Gas Thrust Bearings

A theoretical study on the behavior of an externally pressurized rectangular porous thrust bearing is made using compressible lubricant. A periodic load is imposed on the bearing and the pressure distribution which leads to the determination of stiffness and damping is obtained by small perturbations. The results are calculated numerically using a digital computer. The tabulated theoretical data of a square pad given for a wide range of design variables enable one to use directly in the design. A design procedure of such a bearing is also indicated.