A simple model for gas bubble drag reduction

Abstract

A simple stress model has been developed to explain the observations of reduced drag when small gas bubbles are introduced into a turbulent boundary layer. The drag reduction is caused by a combination of density reduction and turbulence modification. The maximum reduction is obtained when the gas volume fraction approaches the bubble packing limit; the medium viscosity also increases markedly in this limit and becomes the important factor in restricting further reduction in drag. The derived analytical expression represents experimental data well.