Three-Dimensional Lattice Boltzmann Simulations for Droplet Impact and Freezing on Cold Surfaces with a Large Density Ratio

Droplet impact and freezing on solid surfaces are ubiquitous in many natural and engineering processes. Simulating the impacting-freezing process of a droplet is still challenging because it involves the complex multiphase flow and the liquid-solid phase change. This paper establishes a three-dimensional lattice Boltzmann model that considers the effects of contact angle hysteresis and volume expansion to simulate this complex process under realistic conditions. We adopt an enhanced cascaded lattice Boltzmann method to calculate the flow field and a multiple-relaxation-time scheme to solve the liquid-solid phase change model. In addition, a new contact angle model based on the pseudopotential multiphase lattice Boltzmann model is proposed to mimic the contact angle hysteresis. The simulations of droplet impact and freezing on both hydrophobic and hydrophilic surfaces with different surface temperatures and Weber numbers are conducted, and the temporal droplet profile and dimensionless contact length agree well with the experiments, which effectively validates the accuracy and robustness of the present model. Finally, the effects of surface temperatures (0,-15,-30(degrees)C) and Weber numbers (4.4, 19.2, 40.0, 71.1) on droplet dynamics are also examined.