Direct numerical simulations of turbulent flows over superhydrophobic surfaces

Direct numerical simulations (DNSs) are used to investigate the drag-reducing performance of superhydrophobic surfaces (SHSs) in turbulent channel flow. SHSs combine surface roughness with hydrophobicity and can, in some cases, support a shear-free air-water interface. Slip velocities, wall shear stresses and Reynolds stresses arc considered for a variety of SHS microfeature geometry configurations at a friction Reynolds number of Re-tau approximate to 180. For the largest microfeature spacing Studied, an average slip velocity over 75% of the bulk velocity is obtained, and the wall shear stress reduction is 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 microfeature spacing.