Impact Dynamics of a Droplet on Superhydrophobic Cylinders Structured with a Macro Ridge

Abstract

Reducing the contact time of a droplet hitting a solid surface is crucial for many situations. In this work, the dynamic behavior of a low-viscosity droplet on a superhydrophobic surface, which consists of a cylindrical substrate and a macro ridge placed axially on the peak, was numerically investigated <i>via</i> the lattice Boltzmann method. The focus was given to the spreading and the detaching morphology of the droplet at the Weber number <i>We</i> = 0.84-37.8 and the cylinder-to-droplet radius ratio <i>R</i>* = 0.57-5.71. The ridge is found to redistribute the droplet mass and affect the impact outcomes, as well as the contact time. For each <i>R</i>*, a jug rebound, a stretched rebound straddling the ridge, and a split detachment occur sequentially with the increasing <i>We</i>. When <i>R</i>* does not exceed 1.71, the contact time decreases continuously with the increase in <i>We</i>. With <i>R</i>* being taken between 1.71 and 5.14, the contact time initially reduces with <i>We</i> and plateaus after <i>We</i> reaches 10.3. Once <i>R</i>* exceeds 5.14, the split droplets may present as a bestriding shape at <i>We</i> > 30.3 rather than the regular jug shape with a small <i>We</i>. The contact time would be decreased to a second plateau in this case. In most cases, the contact time can be shortened effectively for the droplet on a ridged cylinder compared with that of a smooth cylinder.