Ultrasound Characteristics of Transition Flow Patterns by FVM-FEM

The flow process of oil-water two-phase flow in horizontal pipelines is complex and diverse, with the fluid structure changing over time and the mechanism of flow pattern transformation remains unclear. To achieve visual detection of the oil-water two-phase flow process, a multiphase flow ultrasonic testing and simulation platform was established to study the interfacial effect and relative motion between phases. Using 3D fluid simulation software based on the Finite Volume Method (FVM), a dynamic flow model with oil-water mixed input was built. By extracting the cross-sectional coordinates of the multiphase interface, a 2D geometric meshing model of the measured field was constructed in multi-physics coupling simulation software based on the Finite Element Method (FEM), thus creating a FVM-FEM coupled multiphase flow visualization simulation platform. With ultrasonic excitation and receiving devices set up, the interaction mechanism between oil-water two-phase flow and ultrasound was studied. The results show that during the transition from O/W&W to O/W flow pattern in horizontal pipelines, oil bubbles distribute in the upper part due to density. As the flow rates of oil and water phases increase, the discrete phase region expands, and the number of discrete phases also rises. The ultrasonic attenuation coefficient increases with the expansion of the discrete phase. According to the ultrasonic reflection principle, ultrasound reflects when it meets the interface of two-phase media, and the reflected signal is received by the bottom transducer again. As the discrete phase region expands, the time of flight of the reflected echo reaching the bottom sensor becomes shorter, which can be used to judge the transition degree from O/W&W to O/W flow pattern.