26. Experimental and Numerical Two-Phase Slug Flow Evolution Analysis with a Slightly Downward Direction Change

The intermittent transit of gas and liquid pockets in a pipe is the most distinctive characteristic of the gas–liquid two-phase slug flow pattern. This flow regime is found mainly in oil and gas production and transportation lines. In deep-water oil operations, the pipes must conform to the seafloor, thus causing direction changes in the flow. In this context, the present work presents an experimental and numerical study on gas–liquid two-phase slug flows in ducts with slight direction changes. The pipeline consisted of a horizontal stretch followed by a downward inclined one with −3\(^{\circ }\) and −5\(^{\circ }\) concerning the horizontal in a 26-mm ID, 35.6-m long pipe. Along the experimental circuit, the phases are detected by employing resistive sensors installed in four measuring stations that monitor the characteristic of slug flow parameters, namely the elongated bubble velocity and the unit cell frequency. In the numerical part of this study, a transient methodology based on a simplified two-fluid Lagrangian model was used. In addition, this methodology simulates the gas–liquid regime transitions in pipes with a direction change from horizontal to downward inclined flow. Both the complete and the partial slug dissipations were observed in the downward section. The mean values of the slug flow parameters and the stratification process found both experimentally and numerically presented a good agreement.