Numerical Investigation of Multiphase Air Flow in a Sudden Expansion Channel Using COMSOL Multiphysics

Abstract

Sudden expansion channels are widely encountered in engineering systems such as ventilation ducts, heat exchangers, and energy conversion devices, where flow separation and turbulence significantly affect hydraulic losses and system efficiency. This study presents a numerical investigation of multiphase air flow in a sudden expansion channel using the COMSOL Multiphysics computational platform. The governing Navier–Stokes equations coupled with the k–ε turbulence model were employed to simulate turbulent flow regimes in the Reynolds number range of 2000–7000. Velocity fields, pressure distribution, vortex structures, and phase volume fraction contours were analyzed in detail. The numerical results demonstrate the formation of large-scale recirculation zones downstream of the expansion region, accompanied by substantial pressure losses. A comparative analysis with the classical Armaly experimental data confirms the validity of the numerical model. The obtained results provide a reliable theoretical basis for optimizing sudden expansion geometries and reducing energy dissipation in multiphase flow systems.