The hydrodynamic behavior of high viscous oil-water flow through horizontal pipe undergoing sudden expansion-CFD study and experimental validation

Three pipe configurations for sudden expansion (21-30 mm, 30-40 mm, and 30-50 mm) were selected. The major flow patterns under investigation included core-annular (CAF) and transition from CAF to dispersed flows, with twelve cases considered for numerical runs. The presence of sudden expansion caused the oil core to become more eccentric and thicker far from singularity and without oil contact at the pipe wall during core-annular flow. This is consistent with the flow visualizations that were observed experimentally and discussed in details in the current paper.