Drag reduction by gas injection into turbulent boundary layer: Density ratio effect

A two-dimensional single phase computational fluid dynamics (CFD) model of microbubble-laden flow over a flat plate was used to assess the role of mixture density variation in microbubble drag reduction. The model consisted of Reynolds-averaged Navier–Stokes (RANS) transport equations, a standard k–ω turbulence model, and a convection–diffusion species transport model. Performance of the model was validated with available experimental data and numerical simulations of more advanced multiphase two-fluid model. A parametric study of the density ratio effect on the drag reduction was carried out. The study indicated that simple mixture density variation effect plays one of the major roles in the microbubble drag reduction phenomenon. Also, the influence of the density ratio (the ratio of density of injected gas to that of water) on gas volume fraction profiles was found to be minimal within studied parameter range.