Direct numerical simulation of turbulent channel flow over a liquid-infused micro-grooved surface

Abstract

The effort to reduce drag in turbulent boundary layer flow has long been the motivation of many researches. Recently a superhydrophobic surface (SHS) has drawn much attention as a passive device to achieve high drag reduction. Despite the high performance promised at ideal conditions, maintaining the interface in real flow conditions is an intractable problem. A non-wetting surface, known as the slippery liquid-infused porous surface (SLIPS) or the lubricant-impregnated surface (LIS), has shown a potential for significant drag reduction, as the working fluid slips at the interface but cannot penetrate into the lubricant layer. In the present study, we perform direct numerical simulations of turbulent channel flow over a superhydrophobic surface and a liquid-infused micro-grooved surface to investigate the effects of this surface on the slip at the interface and drag reduction. The flow rate of water is maintained constant corresponding to Reτ∼180 in a fully developed turbulent channel flow, and the lubricant layer is shear-driven by the turbulent water flow. The lubricant layer is also simulated with the assumption that the interface is flat (i.e. the surface tension effect is neglected). The solid substrate in which the lubricant is infused is modelled as straight longitudinal ridges, parallel to the streamwise direction using an immersed boundary method. DNS results show that drag reduction by the liquid-infused surface is highly dependent on the viscosity of the lubricant and the groove geometry.