Mean streaming in reciprocating flow in a double bifurcation

Abstract

This paper reports the mean streaming flow generated in a double bifurcation during reciprocating flow calculated using direct numerical simulations. Motivated by the medical ventilation technique of high-frequency ventilation (HFV), we investigate the potential for mean streaming to be maintained in this geometry as the frequency of reciprocation is increased while concurrently reducing the amplitude (and thereby reducing the volume per cycle). We identify four distinct regimes of flow. The first and second occur at low to moderate frequencies and generate significant streaming flows due to the interaction between Dean vortices that are generated during both the in- and out-flows. The third and fourth occur at high frequencies and produce reduced streaming, due to the reduction in formation length of the Dean vortices. Notably, the fourth regime at the highest frequencies investigated appears to show a switch in the direction of the streaming flow at the wall. Considering the motivating application of HFV, we show that currently employed frequencies are low, and much higher frequencies (and subsequently lower volumes per cycle) could potentially be employed.