Direct numerical simulation to survey the effect of air layer on drag reduction of channel flow with the superhydrophobic surface.

Efficiencies of moving objects such as airplanes, cars, ships, and submarines are adversely affected by friction, which is an important engineering issue. Several approaches have been developed to reduce skin friction drag, especially in turbulent boundary layers. The objectives of the present work are to investigate the effects of superhydrophobic surface (SHS) on the slip velocity and drag reduction in a turbulent flow over SHS having post-distribution geometry. We carried out the direct numerical simulation (DNS) of turbulent channel flows bounded air layer with various slip lengths of SHS. The slip boundary condition was applied to the air cavity interface and a no-slip wall was placed at the top of the channel as well as the top of each post. The interface between water and air was assumed to be a flat surface thus the surface tension effect is neglected. Reynolds number based on the friction velocity and channel half height was fixed as 180. The turbulent kinetic energy budgets including production, dissipation, and diffusion were presented with respect to the slip lengths on post distribution geometry SHS to investigate the drag reduction mechanism.