Numerical simulation of two-phase gas–liquid flow through gradual expansions/contractions

• For high-enough opening angles of the expansion flow separation occurs.
• Pressure recovery across the expansion singularity increases with the volumetric quality.
• The growth of opening angle and elevation of area ratio reduce the pressure recovery.
• A power-law shape velocity profile stems from velocity variation near the smooth expansion.

In the present work, turbulent two-phase flows of air and water are numerically simulated through a smooth area expansion/restriction with a constant opening angle. To model the multiphase flow, a two-fluid approach is adopted in which two sets of governing equations are solved simultaneously for continuous and dispersed phases and the coupling between these phases is forced by proper source terms. An extended version of two-equation k–ε turbulence model is used and the numerical result was validated in comparison to previously published experimental data. The effect of volumetric void fraction, Reynolds number and the opening angle is examined on the pressure distribution across the flow domain.