Effect of oscillation mechanism on the flow exiting fluidic oscillators

Active flow control employing high-momentum oscillating jets from fluidic oscillators has garnered significant attention for flow control applications. Although the effectiveness of these fluidic oscillators is well-documented, the internal and external flow dynamics, particularly in compressible regimes, remain to be fully determined. Fluidic oscillators can be broadly classified into two categories based on their oscillating mechanisms: feedback type (FB) and feedback-free or mixing chamber type (MC). Each design presents distinct advantages; however, a comprehensive comparison of their exit flow fields in compressible conditions has yet to be conducted. This study aims to characterize the flow field in the throat region utilizing detailed stereo particle image velocimetry. The time-averaged velocity fields indicate that, contrary to previous findings, the centerline velocity profiles at the throat section for the FB type do not conform to a top-hat profile. Phase-averaged velocity fields reveal that the MC type, in comparison to the FB type, achieves a higher average jet velocity with reduced variation about the mean. Additionally, the results highlight the presence of a fluid dynamic throat near the geometric throat. In the FB type, this fluidic throat is positioned upstream of the geometric throat, while the MC type displays the fluid dynamic throat downstream. The force generated by the MC type surpasses that of the FB type under identical operating conditions. The characterization of the mass flow rate and momentum flow field in the exit region is crucial for design engineers to assess the applicability of fluidic oscillators in targeted flow control applications.