Many-body dissipative particle dynamics study of the local slippage over superhydrophobic surfaces

The gas-liquid interface (GLI) over superhydrophobic surfaces (SHSs), where the flow slips, is the key to reduce frictional drag in underwater applications. Many-body dissipative particle dynamics simulations are used to explore the slip behavior of a shear flow over a rectangular grooved SHS, and a flat GLI is obtained by tuning the contact angle of the GLI. Due to the slip, the normal profiles of the local velocity, which are perpendicular to the GLI, are curved and shifted away from the linear form near the GLI. Then, a polynomial function is proposed to fit the velocity profile to extract the local shear rate and calculate the slip length. Based on this fitting method, a hybrid slip boundary condition is derived for both longitudinal and transverse flows. That is, the shear stress and slip length are finite near the groove edge, and the stress is nearly zero and the slip length is infinite in the center region of the GLI. This new hybrid slip boundary condition not only explains the inconsistent slip conditions reported in the literature under different groove length scales, but also unifies the existing exclusive slip assumptions.