Exploring Wedge and Bulk Viscous Dissipation in Droplets Moving on Inclined Surfaces by Means of Direct Numerical Simulations

The motion of droplets on inclined surfaces is a ubiquitous phenomenon, yet the underlying dissipative mechanisms remain poorly understood. Employing direct numerical simulations, we investigate water and water-glycerol (85% wt.) droplets (∼25 μL) moving on smooth surfaces, with contact angles of around 90º, at varying inclinations. Our focus is on elucidating the role of wedge and bulk viscous dissipation in the droplets. We observe that, for fast-moving droplets, both mechanisms contribute comparably, while the wedge dissipation dominates in slow-moving cases. Comparisons with existing estimates reveal the inadequacy of previous predictions in capturing the contributions of wedge and bulk dissipation forces in fast-moving droplets. Furthermore, we demonstrate that droplets with identical sliding velocities can exhibit disparate viscous dissipation forces due to variations in internal fluid dynamics.