Numerical Simulation of Elongated Bubbles and Liquid Films in Horizontal Slug Flow

Slug flow poses significant dynamic challenges in multiphase pipeline transport, particularly in complex offshore and Floating Liquefied Natural Gas systems, where conventional one- and two-dimensional models fail to capture the intricate three-dimensional interfacial topologies and transient liquid-film dynamics. To overcome this limitation, the present study develops a three-dimensional transient numerical model based on the coupled level-set and volume-of-fluid (CLSVOF) method within a large eddy simulation (LES) framework, and validates it against high-frequency measurements obtained from a double parallel conductance probe experimental platform. The proposed model successfully resolves phase velocity slip and interfacial morphological evolution, predicting the translational velocity and length of elongated bubbles with a relative error of 2.5% to 6.0%. Local hydrodynamic analysis reveals that a high-speed gas wedge induces rapid liquid displacement and localized stagnation, generating high-frequency pressure surges at the liquid-film front that act as primary drivers of transient mechanical stress. In contrast, increasing the superficial liquid velocity leads to thickening of the underlying liquid film, which provides an effective hydrodynamic buffer that attenuates the trailing-edge hydraulic jump. This damping mechanism suppresses chaotic interfacial fragmentation and promotes a transition toward stable, continuous stratified aeration.