Flow patterns for an annular swirling flow over sudden-expansion

In this work, an experimental study is presented for an annular swirling flow over a sudden-expansion. Both the confined and unconfined cases were examined. The controlled parameters in this experiment included the Reynolds number and the swirl number. Detailed visual observations using smoke streaks were carried out to study the dynamic flow structures of the recirculation zone behind the center body. Laser-Doppler anemometry was also used for the velocity measurements at the jet exit and downstream of the annular flows. The results indicate that the recirculation zones can be clarified into seven distinct flow patterns: stable flow, vortex-shedding, transition, pre-penetration, penetration, vortex-breakdown and attachment. The boundaries of the recirculation zone in various flow conditions were also investigated.