  We demonstrate flow rectification, valveless pumping or AC-to-DC conversion
in macroscale fluidic networks with loops. Inspired by the unique anatomy of
bird lungs and the phenomenon of directed airflow throughout the respiration
cycle, we hypothesize, test and validate that multi-loop networks exhibit
persistent circulation or DC flows when subject to oscillatory or AC forcing at
high Reynolds numbers. Experiments reveal that disproportionately stronger
circulation is generated for higher frequencies and amplitudes of the imposed
oscillations, and this nonlinear response is corroborated by numerical
simulations. Visualizations show that flow separation and vortex shedding at
network junctions serve the valving function of directing current with
appropriate timing in the oscillation cycle. These findings suggest strategies
for controlling inertial flows through network topology and junction
connectivity.
