Optimization Of Lubrication Performance Of Friction Pairs Via Boundary Slip

Hydrodynamic bearings have been widely used in engineering machinery,automotive,aerospace,wind power and other industrial fields.Friction pairs as key components of hydrodynamic bearings,their lubricating properties directly affect the overall performance of mechanical equipment.With the rapid development of modern industrial technology,people are constantly raising the requirements for energy conservation and environmental protection,and therefore higher requirements are placed on the use of friction pairs.Until now,the design and application of high-rate,high-capacity fluid-lubricated friction pairs has been a hot issue.However,the inherent characteristics of the lubricating medium and the machining accuracy of the surface of the friction pair greatly limit the further improvement of this type of performance.To solve this kind of problem,this paper proposes the application of non-wetting materials with low surface energy in hydrodynamic bearings.The slip properties of these materials are used as the theoretical basis,and the fluid film between the friction pairs is considered as the research object.Energy equation and extended Reynolds equation coupled with slip conditions are established.The mathematical model for optimizing the characteristics of hydrodynamic pressure lubrication based on a heterogeneous slip/no-slip surrface in a limited area is constructed.Through the simulation of the model and the verification of the experiments,the following research results had been obtained:Combining the theoretical model of boundary slip proposed by Navier with transient energy equations,a new mathematical model suitable for describing the application of such non-wetting materials is established.The laminar flow between rotating plates is chosen as the research object.The low energy surface of PTFE film is used as the slip material.The simulation of the model predicted the mechanism of temperature rise and resistance change of the fluid under continuous rotation conditions,and explained how the boundary slip control the temperature rise in the long-term operation.In combination with a rotary rheometer,a test platform is built to monitor the temperature to verify the validity of the temperature distribution predicted by the mathematical model.A heterogeneous slip/no-slip surface sample is prepared using PTFE as slip material and PMMA as no-slip material.The test platform is built using a rotary rheometer combined with two mirror-distributed force sensors.The normal forces of the liquid film flowing in the forward direction and in the reverse direction through the heterogeneous surface are monitored.The hydrodynamic effect of the liquid film is qualitatively analyzed under the condition of the constant film thickness in which the wedge effect is eliminated.The theoretical model of the boundary slip is coupled with the classical Reynolds equation to establish an extended Reynolds equation suitable for describing the heterogeneous slip/no-slip in the form of cylindrical coordinates.The boundary conditions are set based on the experimental model and the simulation is solved.In the ramp mode with the speed increasing linearly,the normal forces monitored by the test are compared with the mathematical model to verify the accuracy of the extended Reynolds equation without the wedge effect.A design scheme of heterogeneous slip/no-slip surface for curve splicing is proposed.Two kinds of discrete mathematical models are constructed,namely the quadratic parabola equation and the sinusoidal equation,and the splicing trajectories between the slip zone and the no-slip zone are parameterized.The MATLAB software is used to perform parameterized simulation calculations.The bearing capacity,friction factor,and stiffness of the liquid film are respectively used as the optimization target parameters for simulation and solution.The corresponding slip zones and no-slip zones are obtained according to the requirements of different working conditions.The excellent splicing scheme can further improve the lubrication performance of the liquid film by rationally optimizing the splicing scheme of the targeted slip zone and no-slip zone on the basis of the application of the existing heterogeneous slip/no-slip surrface.A unique distributed form of heterogeneous slip/no-slip surface applied on the sliding pair is proposed.The application of this heterogeneous surface enables the liquid film to generate lateral traction while generating a hydrodynamic pressure between the sliding pairs.A parameterized simulation model of the stitching trajectories between the slip zone and the no-slip zone is designed and a method of multi-sample optimization is implemented.By using this method,a more reasonable combination of slip zone and no-slip zone can be designed.A dimensionless parameter that can be used to characterize the proportion of lateral traction in the entire tangential force generated by the liquid film is defined.Taking the aspect ratio of the calculation region and the exponent describing the power function of the stitching trajectories between the slip zone and the no-slip zone as variables,the dimensionless parameters are optimized,and the configuration of heterogeneous surface that makes lateral traction more significant is obtained.