Flow Structure of an Annular Gas-Liquid Swirling Flow

Abstract

The structure of single-phase and two-phase swirling flow is investigated in this work. Two experimental approaches are presented in this thesis, (i) the three-dimensional velocity measurement of single-phase swirling flow, under the effect of varying flowrate and the presence of bluff bodies, using stereo-PIV, and (ii) the effect of flowrate and obstacles on the air-core stability of two-phase annular swirling flow using high-speed photography.

The swirling flow is generated by a swirl cage, and it is confined in a 41mm diameter plexiglass pipe. The flow is investigated for a wide range of flowrates (130 lpm – 200 lpm). The velocities are measured using a stereo-PIV. It is observed that (i) the averaged tangential velocity profile exhibits a Rankine vortex structure, (ii) the averaged axial velocity profile shows a reversed flow near the center and (iii) the radial velocity profile component reaches it maximum at the center of the pipe generating a radial circulation zone. The size and shape circulation zones are studied using two-dimensional velocity distribution. The velocity vectors of the circulation zone shows that the fluid particles travels radially from one end to the other. The magnitude of the circulation zones increased with flowrate. The presence of a bluff body in the horizontal pipe has a significant effect on both size and shape of circulation zones.

The second of this study focuses on stability of the air-core diameter in an annular swirling two-phase flow. Measurements are performed for an air flowrate range of (0.2 lpm – 1.8 lpm) and a water flowrate of (50 lpm – 100 lpm). The flow was captured using a high-speed camera running at a 2000 fps. All recorded images were processed and analysed using MATLAB image processing toolbox. The effect of two obstacle types is investigated: (i) circular shape and (ii) conical shape. Without any obstacle the swirl two-phase flow presents only one regime, a wavy unstable core. The air core diameter shows large fluctuation range. The mean diameter depends on flowrate and increases with increasing flowrate. The presence bluff body produces new flow structure. An obstacle helped stabilize the air core diameter of the flow, the mean diameter at all flowrate combinations is almost constant. Increasing the flowrate reduced the fluctuations of the air core diameter with the presence of the obstacles.

Date of Award	18 Dec 2023
Original language	American English
Supervisor	Afshin Goharzadeh (Supervisor)