The effect of retraction-rebound dynamics on the contact time of rebounding-coalescing droplets on a superhydrophobic surface with or without a macro-ridge

The effect of retraction-rebound dynamics on the contact time of rebounding-coalescing droplets is investigated via the lattice Boltzmann simulation method on a superhydrophobic surface with or without a macro-ridge. The result shows that the retraction transition from asymmetric to symmetric is triggered by the increased Weber number, when the droplet is split or not split by the ridge. Under the non-split and split conditions, the rebound mode involves the asymmetric/symmetric, asymmetric/symmetric ridge, or right–left non-simultaneous/simultaneous rebound. Under these rebound modes, the coalescence-spreading stage is compressed by the increased Weber number, and thus the retraction-rebound stage being earlier triggered by the increased Weber number, resulting in the enhanced droplet rebound. On the contrary, the droplet rotation is promoted by the increased angular momentum, that is, by the increased Weber number, to enhance the droplet rebound. Because of the enhanced droplet, the contact time is always reduced by the increased Weber number on these two superhydrophobic surfaces.