The flow structures behind an axisymmetric, vertically mounted bluff-body of an annular swirl jet flow were experimentally investigated. By using electrified smoke-wires across the exit plane of the annular swirling flow and a miniature smoke generator embedded inside the bluff-body, flow visualization was accomplished. A Vertical laser-sheet supplied detailed visualization of the dynamic structures of the recirculation bubble behind the bluff-body. Laser-Doppler anemometry was also used for the velocity measurements at the jet exit. Seven typical flow patterns of stable flow, vortex-shedding, transition, prepenetration, penetration, vortex-breakdown and attachment were classified by using the Reynolds number and swirl number parameters. The introduction of a swirling flow into a bluff-body combustor stabilized the recirculating zone. The recirculation length reached a maximum when the flow was from the transition to the pre-penetration region. When the flow was in the penetration region, the size of the recirculation bubble decreased as the swirl strength increased. Finally, by using the Reynolds number and swirl number parameters, the lengths of the recirculation zone were correlated.
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