AbstractThe characteristics of swirling single‐ and two‐phase flows discharging into a sudden pipe expansion were studied in detail by the use of laser‐Doppler anemometry. The results are compared with those for the comparable non‐swirling case. The central recirculation zone established for a swirl number of 0.56 was found to have an annular shape, which was a result of the subcritical nature of the flow and the area contraction at the end of the test section.The behaviour of the particles in both swirling and non‐swirling flow was studied by flow visualization, particle concentration and velocity measurements. Initially, the spreading of the particle jet is about the same for both cases owing to the particle inertia. In the middle of the recirculation bubble the particles start to spread more rapidly under the acting of centrifugal forces established in a swirling flow. This finally results in a high concentration of particles near the wall of the test section and a particle‐free region in the core of the vortex. The numerical simulations of the non‐swirling flow showed good agreement for both the gas and particle phases in comparison with the experim