Cavitation-enhanced biphasic lubrication performance induced by bio-inspired armor textures

Surface texturing serves as an effective method for enhancing lubrication performance in high-speed sliding contacts operating in the fluid-film lubrication regime. Inspired by the superhydrophobicity of the lotus leaf, which arises from the synergy between its hierarchical micro/nano-structures and epicuticular wax coating, a surface texture with an inverted-pyramid architecture was developed. Its interior is coated with a low-surface-energy bio-inspired layer exhibiting aerophilic properties. The top planar surface of the texture acts as a protective armor for the bio-inspired coating during sliding, contributing to friction reduction and enhanced wear robustness. Employing a dynamic mesh technique with controlled oil-film thickness, the friction-reduction mechanism of the armor texture with stabilized bio-inspired coatings was investigated. To further enhance the drag reduction performance, three composite armor-textured configurations (1-0.3, 1-0.5, and 1-0.7) were designed, featuring a centerline-convergent monosymmetric distribution. Furthermore, the exceptional lubrication performance of the armor texture was validated using a cavitation visualization test rig. The bio-inspired coating with low surface energy optimizes pressure distribution and expands the cavitation vapor zone. Compared to the single armor texture (SAT), the 1-0.7 bio-inspired composite armor texture (CAT) demonstrates remarkable improvements: a 179.6% increase in vapor volume fraction, a 19.3% increase in oil-film thickness, and a 50.4% reduction in the friction coefficient. The synergy between the composite armor texture and the bio-inspired coating facilitates rapid formation and stabilization of a gas layer, which significantly enhances load-bearing capacity while substantially reducing friction at the sliding interface.