  Droplet mobility under shear flows is important in a wide range of
engineering applications, e.g., fog collection, and self-cleaning surfaces. For
structured surfaces to achieve superhydrophobicity, the removal of stains
adhered within the microscale surface features strongly determines the
functional performance and durability. In this study, we numerically
investigate the shear-induced mobility of the droplet trapped within porous
surfaces. Through simulations covering a wide range of flow conditions and
porous geometries, three droplet mobility modes are identified, i.e., the
stick-slip, crossover, and slugging modes. To quantitatively characterise the
droplet dynamics, we propose a droplet-scale capillary number that considers
the driving force and capillary resistance. By comparing against the simulation
results, the proposed dimensionless number presents a strong correlation with
the leftover volume. The dominating mechanisms revealed in this study provide a
basis for further research on enhancing surface cleaning and optimising design
of anti-fouling surfaces.
