Effect of superhydrophobicity on the flow past a circular cylinder in various flow regimes

The flow over a superhydrophobic and a smooth circular cylinder is investigated using particle image velocimetry-based experiments. The objective is to understand the effect of surface modification on the ensuing flow. The experiments are conducted over a wide range of Reynolds numbers, , thereby uncovering the effect of superhydrophobicity in various flow regimes of a cylinder wake. Superhydrophobicity is found to substantially affect the flow. An increased recirculation length is observed for the superhydrophobic cylinder in the steady regime. The onset of vortex shedding is delayed for the superhydrophobic cylinder. The superhydrophobic cylinder helps in an early rolling-up of vortices; therefore, the recirculation length reduces in unsteady regimes. The velocity deficit experienced by the superhydrophobic cylinder wake is comparatively less and the effect is more profound in the range 300-860. A maximum drag reduction of 15 % is observed at . The Reynolds shear stress and turbulent kinetic energy values are higher for the superhydrophobic cylinder in the unsteady regime. Also, the peaks of the turbulent wake parameters lie closer to the superhydrophobic cylinder compared to the smooth cylinder. The effect of superhydrophobicity on coherent structures is examined using proper orthogonal decomposition, and a considerable difference in the wake structure is noticed at . A larger number of coherent structures and change in vortex shedding pattern to are observed in the near wake of the superhydrophobic cylinder. The results of this study show that surface modification can reduce the drag coefficient and have a profound effect on the near wake.