Creeping flow dynamics over superhydrophobic ball: Slip effects and drag reduction A Physicochemical and engineering aspects

Slip and drag over superhydrophobic ball in the creeping flow regime (Reynolds number 1) of the system, air is trapped in the surface asperities without formation of film (plastron). The flow over SH ball is modeled using the stream function formulation, that incorporates wall-slip and relates it to the enhanced settling velocities and drag reduction. Slip length decreases (178–24μm) with the increase in Reynolds number, establishing the dependence of slippage on flow apart from surface morphology. The drag reduction is comparatively low 8% due to the absence of plastron. A component based analysis reveal that form drag contributes towards one-third of the total drag while skin drag and normal stress drag contribute towards the remaining two-third. The skin drag takes over the normal stress drag with the increase in Reynolds number, eventually replacing it. The experimental method and modeling constitute a generic technique for evaluating the potential of SH surface to reduce drag.