Effect of swirl on fluctuation of pressure drop in a gas–liquid slug flow

Slug flow as one of the typical two-phase flow patterns occurs widely in industry. The fluctuating phenomenon in slug flow is harmful to the pipeline system and should be suppressed. Flow-pattern modulation by swirl has been widely used to satisfy practical application. In this work, influences of swirl on pressure gradient and interface morphology in a gas–liquid slug flow were studied by visualization experiments. The results showed that slug flow will transform to swirling intermittent flow when the gas and liquid velocity is relatively high. In this case, pressure drop in the slug flow is higher and its fluctuation within a relatively narrow range compared with those in a non-swirl slug flow; the probability density function distribution is more concentrated in the swirling intermittent flow; the slug flow transforms to the flow pattern altering between gas column and gas slug. The slug flow was kept downstream of the swirler when the gas and liquid velocity is relatively low. In this case, effects of swirl on both pressure drop and interface morphology are not obvious. Along the streamwise direction, the morphology interface, fluctuation of pressure drop and pressure signals showed that the swirling intermittent flow gradually transforms to non-swirl slug flow. Finally, the transition boundaries between these flow patterns were proposed and compared with other published transition boundaries in swirling and non-swirling flows.