A numerical study of superhydrophobic surfaces with riblet in turbulent channel flow

The development of more efficient methods for simulating superhydrophobic (SH) surfaces of the turbulent boundary layer continues to be the subject of interest. In this study, numerical simulations were performed to explore the effect of the SH surfaces in wall-bounded flows. For this purpose, turbulence models including RANS, DES and LES were employed. The Navier's slip velocity was used over the superhydrophobic wall as for the slip conditions. The numerical results were compared and validated with the experimental data in terms of the slip velocity, skin friction and Reynolds stresses over SH surfaces. Then, the developed models were further extended to study the drag reduction effect of superhydrophobic textures with rectangular riblets. The outcomes showed that the combination of SH surface and rectangular riblets revealed a better performance. This is because of the surface slip caused by the SH surface and the secondary vortex effect created by grooves. Our results indicated that Reynolds stresses of slippery grooved surfaces were higher than that of the case with grooves assumed as a shear-free condition. More notably, results showed the inaccuracy of the previous assumption of the shear-free condition for the geometrically simplified grooved SH textures.