| The mechanisms affecting mixing, entrainment, noise generation, and transition from laminar to turbulence of a free jet have been carefully studied over the years, but are not yet fully understood and the research continues today. This work experimentally investigates the active flow control of axisymmetric, transitional, single-phase and particle-laden jets using a single synthetic jet or a continuous control jet located near the main jet exit. The 3-D interaction was obtained by using a 3-D rendering technique.; For the single-phase jet, the synthetic jet interacts with it through: (1) a direct impact (momentum transfer), and (2) amplification of the main jet's vortical structures. The synthetic jet angle (WRT the main jet centerline) and its upstream location (i.e., inside the main jet nozzle), were investigated. The synthetic jet penetrates the main jet, creating large streamwise vortical structures and increasing the main jet width. Activating the synthetic jet farther upstream decreases the effectiveness of the synthetic jet. By comparison, a continuous control jet, which utilizes only direct impact, only vectors the main jet away from the control side. Higher Reynolds number main jets are shown to be less receptive to both flow control methods. Examining the transitory interaction, the effect of the synthetic jet is felt throughout the measurement domain after only two synthetic jet cycles, reaching its periodic state after only four cycles. The main jet's response to the actuation is shown to be directly linked with the synthetic jet's response to the driving signal.; In the second thrust, the effects of active flow control on three Stokes number particle-laden was examined. Each was shown to be influenced by the direct impact of the synthetic jet impulse (by momentum transfer to the particles) as well as the indirect influence of the coherent vortical structures. The direct impact vectors the particles away from the synthetic jet, while the formation of large vortical structures indirectly affects particle spreading throughout the measurement domain. By comparison, a continuous control jet only pushes the particles away from it. The lowest Stokes number particles respond similarly to the single-phase flow, while the higher Stokes number particles are less responsive to the carrier fluid and only follow the strong vortical structures, which suggests that preferential concentration depends on both the Stokes number as well as the strength of the vortical structures. |
