THE AXISYMMETRICAL RECIRCULATION WAKE FLUSHED BY A CENTRAL JET

The flow structures in a circular-disk-generated recirculation wake wi th a centrally flushing jet were studied by the smoke-wire and schlier en flow visualization techniques. The smoke-wire was applied to the lo w velocity regime to reveal the detailed vortex structures in the reci rculation bubble, whilst the schlieren technique was employed in the h igh velocity regime to show the characteristics of the penetration and mixing. The smoke and schlieren photographs show prominent features o f the interaction between the central jet and the recirculation flow. Comprehensive flow patterns and the behavior in each characteristic fl ow regime were investigated. Four typical characteristic flow regimes, pre-penetration, transition, penetration, and no-recirculation, were identified for different jet velocities in the near wake region. The s hear and mixing processes were found to be different in each regime. D ensity effects on the formation of recirculation are discussed. The co ntours of the separation surfaces and the lengths of the recirculation zone are correlated with nondimensional parameters. The recirculation length reaches a maximum in the transition region, and shortens with increasing central-to-annular jet velocity ratio in the penetration re gion.