Effect of the slip length on the flow over a hydrophobic circular cylinder

Abstract The laminar flow (Reynolds number ranging from 60 to 180) past a hydrophobic circular cylinder is conducted by the time-dependent simulation with focus on the effect of dimensionless slip length, L S (ranging from 0.01 to 0.25), on total, viscous and pressure drag coefficients. It is found that the viscous drag plays a major role in drag reduction, for low Reynolds ( Re < 100) and small slip length ( L S < 0.02). When the Reynolds number and slip length are large enough, the decrease of total drag mainly depends on the pressure drag. The pressure drag coefficient increases with the Reynolds number when L S ranges from 0 to 0.02. For L S of 0.05, however, it has a different trend. Due to small proportion of viscous drag to total drag coefficient, the effect of viscous drag on the total drag is less important. The adverse pressure gradient appears on the circular cylinder and increases with the slip length. The pressure distribution is mainly affected by the vorticity gradient, fluid convection and the stability. Meanwhile, as Reynolds number equals to 100, the separation point moves downstream. This results in the increase of vortex shedding frequency and the decrease of vortex intensity at L S ranging from 0 to 0.11. As slip length increases to 0.25, the flow is stable. These results can provide useful information on the drag reduction control of the cylinder surface.