Droplet impact on superhydrophobic GCr15 bearing steel surface: Droplet morphology evolution and heat transfer under local hydrophobicity failure

Superhydrophobic surface design serves as a critical strategy for bearings to mitigate intrusion and erosion induced by water and other corrosive media. However, existing research has not yet clarified the morphological evolution and heat transfer mechanisms of intrusive water droplets following local superhydrophobic failure on bearing steel surfaces. To address this gap, a combined approach of CFD simulations and experimental tests was adopted to investigate the effects of Weber number ( We ) and Wetting Overlap Ratio ( A* ) on the heat transfer characteristics during droplet impact on bearing steel surfaces with local superhydrophobic failure, and the underlying mechanisms governing droplet morphological evolution were elucidated. The results demonstrate that the spreading, breakup, and jetting behaviors of droplets upon surface impact are synergistically governed by A* and We , based on which a predictive model for the maximum droplet spreading radius was developed. Furthermore, the formation modes of different types of satellite droplets were identified, and their formation boundaries were quantitatively defined. It was also found that the motion of satellite droplets is predominantly driven by the momentum generated during the lamella retraction stage. Additionally, the results show that the transient wall heat transfer is significantly enhanced with increasing We , and the peak wall heat flux appears in the parameter range of 0.5 < A* < 1. This study lays a foundation for thermal analysis and secondary water contamination assessment of bearing surfaces after superhydrophobic failure, and provides theoretical support for the design of water erosion-resistant structures and the optimization of thermal management for GCr15 bearing steel.