Numerical study of droplet impact dynamics on micropillar arrays of different shapes: Effects of Weber number and wall contact angle

This paper employs the Volume of Fluid (VOF) method and the Blake dynamic contact angle model to conduct three-dimensional simulations of droplet impact on microstructured arrays with square, cylindrical, and triangular pillars. It investigates the surface flow characteristics following impact, analyzing variations in spreading patterns, spreading factors, and height factors under different Weber numbers (We) and contact angles (θ). Additionally, the study extends the existing model for predicting the maximum spreading factor. The results show that the geometrical configuration of the pillars and We significantly influences the droplet spreading pattern and plays a key role in the formation mechanism and number of secondary droplets. The groove-driven effect exhibits strong geometrical dependence, markedly affecting the jet length, the secondary droplet formation, and the power-law exponent of the maximum spreading factor. In the triangle top angle direction, the pinning effect is pronounced while the groove-driven effect is weaker, resulting in restricted spreading. At low We, the bubble retention influences the evolution of the droplet central height. Variations in the θ primarily affect the retraction process and the formation of secondary droplets, while having a limited impact on the maximum spreading factor. The fitting analysis indicates that the existing power–law correlation between the maximum spreading factor and We remains valid for droplets impacting micropillar arrays, and the extended prediction model shows good agreement with the numerical results.