Moradi Mostafa, Rahimian Mohammad Hassan, Chini Seyed Farshid
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
Phys Rev E. 2019 Jun;99(6-1):063111. doi: 10.1103/PhysRevE.99.063111.
The vibration-induced droplet shedding mechanism on microstructured superhydrophobic surfaces was simulated using the lattice Boltzmann method. The numerical simulations of natural droplet oscillations for various surface structures show that the natural frequency of the droplet is strongly dependent on surface morphology. The results show good agreement with basic theoretical values. Furthermore, simulations of the motion of the droplet subjected to vertical surface vibration demonstrate that droplets in the Cassie wetting state are easily removed from the surface, whereas for Wenzel state droplets, pinch-off occurs and only partial removal is possible. Microstructure spacing was found to be a key factor in the shedding process. On a surface with small microstructure spacing, the increased surface adhesion leads to a decrease of droplet departure velocity. In contrast, for large roughness spacing, the droplet is impaled on the microstructures, which causes the departure velocity to decrease. Reperforming the simulations under different vibration intensities reveals that as the vibration amplitude is increased, the optimum frequency for droplet removal decreases. The findings of this study shed light on the underlying mechanisms involved in forced vibrations of droplets and can be helpful in engineering applications in which droplet shedding processes are critical.
采用格子玻尔兹曼方法模拟了微结构超疏水表面上振动诱导的液滴脱落机制。对各种表面结构的自然液滴振荡进行的数值模拟表明，液滴的固有频率强烈依赖于表面形态。结果与基本理论值吻合良好。此外，对垂直表面振动作用下液滴运动的模拟表明，处于Cassie润湿状态的液滴很容易从表面去除，而对于Wenzel状态的液滴，会发生夹断现象，只能部分去除。发现微结构间距是脱落过程中的一个关键因素。在微结构间距小的表面上，表面附着力增加导致液滴离开速度降低。相反，对于大粗糙度间距，液滴会刺入微结构中，这导致离开速度降低。在不同振动强度下重新进行模拟表明，随着振动幅度的增加，液滴去除的最佳频率降低。本研究的结果揭示了液滴强迫振动所涉及的潜在机制，并且对液滴脱落过程至关重要的工程应用可能有所帮助。
