The Nature of “Searching” Vortices in Fluidic Logic Driven by a Switching Jet

Fluctuating jets energized by local excitations can perform operations similar to those of electric circuits but without electricity or moving parts. Some have termed these circuits “fluidic computers.” It is known that fluidic logic in a bistable two-channel splitter arrangement can occur at predictable frequencies, but uncertainty surrounds the internal flow character and how fine-scale hydrodynamic details control its self-driven oscillations. Additionally, flow rates, switching frequencies, and switching pressures “chosen” by the fluidic logic are not known a priori. A joint computational/experimental study has revealed that three families of vortex rollers compete for space and momentum, searching for preferred trajectories. The rollers were strongly three-dimensional (3D) like horseshoe vortices, but vortex tube spanwise asymmetry, in an otherwise symmetrical flow passage, was pervasive during vortex searching. Bending and localized compression were evident. Reynolds stress analysis revealed that streamwise autocorrelation dominated much of the oscillation cycle, with wall-normal normal stresses being slightly lower and then spanwise normal stresses being about half of that; uv stresses generally changed signs when the jet flipped directions. The mechanism by which the flow naturally cycles between a direct and indirect flow passage without any external influence is discovered. Specifically, at discharge pressures exceeding $≈18%$ or below $≈8%$ of the feed total pressure, conditions are favorable for the searching vortices to choose an alternate path, engaging the cyclical fluid switch and rerouting the jet up to approximately half of its maximum deflection.