Large Eddy Simulation of Turbulent Flow over Hydrophobic Surfaces

In recent years, extensive efforts have been made on the design and fabrication of surfaces having the ability to reduce viscous drag. In this article, the effect of hydrophobic surfaces on viscous drag has been investigated using large eddy simulation of a turbulent channel flow. Hydrophobic surfaces are known by their ability to trap an air layer and by the existence of slip boundary conditions on them. Using slip boundary condition, the viscous drag is reduced and the turbulence intensities and the near-wall eddies are weakened considerably. In this paper, the slip velocities and the shear stresses at the wall for different slip lengths of hydrophobic surfaces, at the viscous Reynolds number of Re ≅ 180, τ have been investigated. For slip lengths greater that 10-5 m, an average slip velocity of more than 18% of the average velocity has been obtained and the wall shear stress has been reduced by more than 60%.The results show that, the slip length to have a tangible effect on turbulence should be greater than a certain amount.