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| Dynamic Characteristics of Metal Liquid Film at Armature-Rail Interface in High-Speed Sliding Electrical Contact |
| Lou Jianyong1, Feng Yigong1, Liu Qian1, Yan Jianghan1, Qie Jiahui2 |
1. School of Electrical Engineering Xi'an Jiaotong University Xi'an 710049 China;
2. Baoding Power Supply Subsidiary Company State Grid Hebei Electric Power Supply Co. Ltd Baoding 071000 China |
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Abstract In the context of electromagnetic launch, a prototypical high-speed sliding electrical contact process, the dynamic characteristics of the metal liquid film at the armature-rail interface play a decisive role in ensuring electrical contact stability and energy transfer efficiency. Aiming to investigate the regulatory mechanisms governing liquid film behavior under high-speed conditions, this study constructs a comprehensive hydrodynamic lubrication model that integrates roughness correction and viscosity-pressure coupling and systematically analyzes the impacts of rail surface roughness, roughness distribution patterns, and armature velocity on the armature surface melting rate, liquid film pressure distribution, and film thickness evolution.
The results reveal that the surface roughness of the rail is the dominant factor regulating the melting rate of the armature and the distribution of the liquid film thickness. As the roughness increases, the melting rate on the armature surface significantly rises, while the time to reach a fully lubricated state is correspondingly delayed. When the roughness exceeds a critical threshold, the proportion of the distance over which energy is more efficiently converted into armature kinetic energy under full lubrication significantly decreases, thereby reducing the overall energy conversion efficiency of the launching system. In contrast, the pattern of roughness distribution has a relatively minor effect on the melting rate under high-speed conditions. However, the texture orientation notably modulates the liquid film pressure distribution by altering the shear flow path within the liquid film. The liquid film pressure distribution exhibits pronounced edge effects, with peak values primarily concentrated near the inner region close to the armature head. As the armature velocity increases, the pressure peak demonstrates a non-monotonic trend characterized by an initial increase followed by a decrease.
At low speeds and pressures, the viscosity-pressure coupling effect causes only limited viscosity increases due to weak intermolecular interactions within the liquid film. As a result, its impact on flow resistance and melting rate is negligible. As velocity increases, an exponential rise in liquid film pressure triggers the viscosity-pressure coupling mechanism of the Roelands model, causing nonlinear growth in the viscosity of liquid metal. This leads to significant shear heating within the film, while the high-viscosity state reduces its thermal conductivity, thereby accelerating the melting of the armature surface. Analysis indicates that neglecting the viscosity-pressure coupling effect under high-speed launch conditions leads to an underestimation of the metal liquid film's viscosity, which can result in inaccurate predictions of the liquid film's dynamic behavior. To ensure model fidelity and proper design, we recommend integrating a dynamic viscosity correction mechanism based on viscosity-pressure coupling in engineering applications of electromagnetic launch systems.
This study deepens the understanding of metal liquid film dynamics in high-speed sliding electrical contacts through a multi-scale coupling analysis. However, further investigation is needed into the temperature dependence of the viscosity-pressure coefficient, the non-Newtonian behavior of liquid metals under extreme shear, and the long-term impact of rail surface evolution on film stability across repeated launches. These challenges necessitate combined approaches involving high-speed dynamic microscopy, in-situ material characterization, and molecular dynamics simulations.
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Received: 21 May 2025
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2026, Vol. 41 
