Numerical study of a water droplet impacting on a moving hydrophobic wall using a 3D lattice Boltzmann method

Understanding the dynamics of a water droplet after impacting on a moving wall is significant for many applications such as repelling rain droplets from a vehicle. In this paper, a water droplet impacting on a moving hydrophobic wall is studied numerically using a 3D lattice Boltzmann method (LBM). The accuracy of the present model is validated by comparing with existing correlation equations for the maximum spread factor and the contact time. It is found that the droplet spreads into an asymmetric shape after impacting on the moving wall owing to the momentum transfer from the wall to the droplet. The droplet deformation increases with the increasing of the wall velocity. Because of different bouncing behaviors of the droplet, the effect of the wall velocity on the droplet contact time varies with contact angles: the droplet contact time decreases with the increasing of the wall velocity for θ = 156°, while the droplet contact time increases with the increasing of the wall velocity for θ = 130°. It is also found that the droplet bouncing motion will be suppressed at a high wall velocity for θ = 130°. Finally, a map in terms of the Weber (We) number versus the contact angle (θ) is obtained, showing that a larger critical contact angle is required for droplet rebounding from a moving wall. This work provides a guidance that a moving wall needs to be more hydrophobic than a stationary wall to repel water droplets. Graphical abstract: [Figure not available: see fulltext.]