The characteristics of severe slugging flow in two types of riser systems are studied, including occurrence region, pressure fluctuations at riser base, cycle time, and liquid slug length. The flow pattern map in S-shaped flexible riser is compared with the classical severe slugging flow transition criteria. The experimental results show that the severe slugging cycles are similar in two types of risers. However, there is a second growth on the pressure fluctuations in the S-shaped riser compared with the vertical riser. The period duration in the S-shaped riser is longer, but the liquid slug length is shorter. The occurrence region of severe slugging flow in the S-shaped riser is smaller than that in the vertical riser.
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