Perturbation of a downward liquid flow by a stationary gas slug

The effect of a stationary gas slug on the hydrodynamics of a downward liquid flow in a pipe is investigated. The electro-diffusion technique is used to measure the mean and fluctuating viscous stresses on the wall below the gas slug and in the liquid behind the slug base. It is shown that at a constant liquid velocity the friction beneath the slug is determined by the distance from its nose. The flow structure perturbation due to a single slug is recorded at distances greater than 25 pipe diameters from the slug base.