LES of stratified-wavy flows using novel near-interface treatment*

The pressure drop in horizontal stratified wavy flows is influenced by interfacial shear stress. The near-interface behavior of the lighter phase is akin to that near a moving wall. We employ a front-tracking code, {\it Blue}, to simulate and capture the near-interface behaviour of both phases. {\it Blue} uses a modified Smagorinsky LES model incorporating a novel near-interface treatment for the sub-grid viscosity, which is influenced by damping due to the wall-like interface, and enhancement of the turbulent kinetic energy (TKE) due to the interfacial waves. Simulations are carried out for both air-water and oil-water stratified configurations to demonstrate the applicability of the present method. The mean velocities and tangential Reynolds stresses are compared with experiments for both configurations. At the higher Re, the waves penetrate well into the buffer region of the boundary layer above the interface thus altering its dynamics. Previous attempts to capture the secondary structures associated with such flows using RANS or standard LES methodologies have been unsuccessful. The ability of the present method to reproduce these structures is due to the correct estimation of the near-interface TKE governing energy transfer from the normal to tangential directions.