Eliminating gas accumulation in horizontal diverging channels under two-phase flow using upstream solid cross-flow steps

Gas accumulation in gas–liquid two-phase flows creates major challenges in centrifugal pumps and diverging channels, as trapped gas in low-pressure separation zones promotes flow separation, reduces pressure recovery, and increases the risk of system failure. To address this, the present study proposes a novel and simple passive control strategy using upstream cross-flow solid steps of varying heights (2, 5, and 8 mm) in a horizontal diverging channel. Controlled experiments combining Laser Doppler Anemometry (LDA), high-speed imaging, and pressure measurements were performed to evaluate the effect of step height on flow separation, bubble behavior, and pressure recovery. Results show that steps of 5 mm and 8 mm could successfully eliminate gas accumulation and significantly improve pressure recovery compared to the baseline without steps, while the 2 mm step had only a marginal effect. These improvements are attributed to enhanced bubble breakup, increased vertical dispersion, and elevated turbulence, while reducing flow separation. The findings not only provide benchmark data for validating two-phase flow models but also offer practical design guidelines for improving gas handling in centrifugal pumps and related industrial systems.