| LIU Minghai,LI Shuyi,GUO Feng,LIANG Peng,AN Yukun.#$NP Simulation Study on Squeeze Spreading and Reflux Characteristics of Limited Lubricating Oil on Wetting Gradient Surfaces[J],54(1):181-190 |
| #$NP Simulation Study on Squeeze Spreading and Reflux Characteristics of Limited Lubricating Oil on Wetting Gradient Surfaces |
| Received:January 08, 2024 Revised:March 29, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.01.017 |
| KeyWord:wetting gradient squeeze spreading reflux limited lubricating oil numerical simulation dynamic mesh |
| Author | Institution |
| LIU Minghai |
School of Mechanical & Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
| LI Shuyi |
School of Mechanical & Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
| GUO Feng |
School of Mechanical & Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
| LIANG Peng |
School of Mechanical & Automotive Engineering, Qingdao University of Technology, Shandong Qingdao , China |
| AN Yukun |
School of Mechanical Engineering, Shandong University of Technology, Shandong Zibo , China |
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| Abstract: |
| In mechanical motion pairs, the phenomenon of limited lubricating oil undergoing squeeze spreading and reflux is prevalent, directly influencing the lubrication supply state in the contact pairs. The surface wetting property emerges as a critical factor impacting the flow of lubricating oil, and consequently plays a pivotal role in the lubrication performance of the contact pairs. Therefore, it is imperative to investigate the flow characteristics of lubricating oil on surfaces with wetting gradients and unveil their operational mechanisms. Utilizing the Volume of Fluid (VOF) model in conjunction with dynamic mesh techniques, a dynamic model was established for the squeeze spreading and reflux of minute lubricating oil droplets on surfaces with wetting gradients. Numerical simulation methods were employed to explore the effects of the contact angle on the oleophilic track's outer side, track width, and lubricating oil viscosity on the processes of droplet spreading and reflux. The lubricating oil on surfaces with wetting gradients rapidly spread after being subject to pressure. Once the pressure diminished, the lubricating oil automatically underwent reflux. During the reflux phase, significant pressure gradients and velocity vortices were observed within the lubricating oil. By adjusting the contact angle of the oleophobic region (from 67° to 130°), the degree of oleophobicity on both sides of the track was altered, the maximum spreading coefficient β and the maximum wetted area An decreased by 23.6% and 14.3%, respectively. The growth time point of the height coefficient hn advanced by 57.2%, and the complete reflux time decreased by 76.9%. Increasing the track width revealed that, as the dimensionless track width wn increased from 0.8 to 1.4, the maximum β and hn growth time point remained stable, while the maximum An increased by 64.2%, and the complete reflux time decreased by 39.4%. Concerning the physical properties of the lubricating oil, the increase in lubricating oil viscosity (from 0.032 Pa.s to 0.108 Pa.s) resulted in a reduction of 13.5% in both the maximum β and the maximum An. However, the hn growth time point was delayed by 72.2%, and the complete reflux time was extended by 58.3%. Furthermore, within the low viscosity range, even though the smallest viscosity increment occurred between adjacent viscosity values (0.032 Pa.s to 0.046 Pa.s), the reflux velocity and the rate of decrease in An were the most pronounced. In conclusion, surfaces with wetting gradients can inhibit lubricating oil spreading and promote reflux, with internal pressure gradients being one of the primary reasons for reflux. As the degree of oil repellency increases on both sides of the track, the inhibitory effect on spreading and the promoting effect on reflux are further enhanced, leading to an increase in reflux velocity and a reduction in complete reflux time. Enlarging the oleophilic track width enhances the stabilized wetted area and shortens the complete reflux time. However, excessively wide tracks lead to overly dispersed oil distribution, while excessively narrow tracks prolong reflux time. Additionally, within the low viscosity range, wetting gradient surfaces exhibit a more pronounced impact on lubricating oil reflux. An increase in lubricating oil viscosity results in a decrease in both the maximum spreading coefficient and the maximum dimensionless wet area. This leads to a shorter reflux distance, a relatively delayed point of growth in the height coefficient of the liquid film center, and an extension of the complete reflux time. |
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