Comparative Study on Experiment and Numerical Simulation of Annular Multiphase Flow

Annular gas–liquid flow is more complex than the flow in circular pipes because the inner and outer walls can support two liquid films. This study addresses the limited quantitative information available for inclined, dual-size annuli by combining controlled air–water experiments with three-dimensional transient computational fluid dynamics (CFD). Tests were conducted in a 5 m annular test section with a 38.5 mm tubing outer diameter and casing inner diameters of 75.9 and 62 mm at inclination angles of 45° and 90°. The experimental matrix covered air inlet velocities of 0.295–3.00 m/s and water inlet velocities of 0.20–2.00 m/s. Flow morphology was recorded by a high-speed camera, while pressure drop and liquid holdup were measured by differential pressure transducers and a conductivity probe, respectively. A transient volume-of-fluid (VOF) model coupled with the renormalization-group (RNG) k-ε turbulence model reproduced the same test section. The numerical and experimental flow morphologies agree for bubbly, slug, and annular flow. The predicted pressure drop follows the experimental trend with R2 = 0.92 and an average absolute error of 7.91%, whereas the conventional Beggs-Brill, Mukherjee, Aziz, Hasan, and JPI correlations show larger average absolute errors. The principal advance of this work is a consistent experimental-numerical assessment of dual-film annular flow under two annulus sizes and two inclination angles, together with an explicit account of the remaining validation and measurement limitations. The results provide a basis for improving pressure-drop prediction in inclined coiled-tubing gas-lift wells.