Flow past a rotating circular cylinder with superhydrophobic surfaces

Superhydrophobic surfaces (SHSs) are widely reported and applied to modify flow features. In this work, the two-dimensional flows past a rotating circular cylinder with SHSs are studied to explore its effect. The present numerical simulations take SHSs into account by alternating shear-free and no-slip boundary conditions with different gas fraction (GF) for non-dimensional rotation rates of 100. Numerical results indicate that SHSs can obviously modify the critical rotation rates of vortex shedding, frequency of vortex shedding, force acting on the cylinder as well as the instantaneous and mean velocities near the cylinder. Moreover, such variation exhibits diverse behaviors in different flow regimes. For instance, both drag enhancement and drag reduction are found in the presence of SHSs. For the rotation rate corresponding to a vortex shedding regime, the drag of cylinder is reduced by SHSs. On the contrary, SHSs enhance the drag of cylinder in the steady regime. SHSs play different roles in different flow regimes so that the first critical rotation rate decreases monotonically with the increase of GF, while the second and the third critical rotation rates increase monotonically with increasing GF. The effect of SHSs in such flow could have some potential application.