Direct Numerical Simulations of Turbulent Flows over Superhydrophobic Surfaces

Direct numerical simulations are used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are considered for a variety of superhydrophobic surface micro-feature geometry configurations at a friction Reynolds number of Re$_{\tau }$ = 180. For the largest micro-feature spacing of 90$\mu $m an average slip velocity over 75{\%} of the bulk velocity is obtained, and the wall shear stress reduction is nearly found to be nearly 40{\%}. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress, but is offset by a slip velocity that increases with increasing micro-feature spacing.