The origin of the self-sustained oscillations in fluidic oscillators and the role of some internal dimensions

Fluidic oscillators (FOs) are commonly used in active flow control (AFC) applications to delay the boundary layer separation from any bluff-body. These devices are also employed in combustion chambers to enhance mixing, or in heat transfer applications to promote the generation of a turbulent boundary layer and therefore enhance cooling. The frequency associated with the self-sustained oscillations generated by the FO depends on the Reynolds number and the internal dimensions of the oscillator. In fact, this work aims to clarify which are the most relevant FO internal dimensions capable of modifying the outlet flow frequency and which is the origin of the self-sustained oscillations. Two main internal modifications were considered. Initially, the feedback channel (FC) width is modified, but differently from previous research papers, then in the present study, each FC width is associated with a different mixing chamber (MC) inlet width, and this small modification in the inlet width is proved to have large implications in the FO outlet frequency. In fact, the influence of the MC inlet width is found to be more relevant than the modification in the FC width. The modification of the MC outlet inclination wall is also addressed in the present study. The MC pressure and the interaction between the main jet and the reverse mass flow jet are highly influenced by this particular modification. When analyzing the forces acting on the main jet as it enters the MC, it is observed that, regardless of the internal modification performed, the pressure forces play the most important role; therefore, we conclude that for the present FO configuration, the self-sustained oscillations are pressure driven.