Periodic flow oscillation of semi-dilute polymer solution in microchannel with pillar arrays

This study investigates flow instabilities of semi-dilute polymer solutions in microchannels with regularly patterned circular micropillars. A semi-dilute hydrolyzed polyacrylamide solution was employed as the working fluid. When the Weissenberg number (Wi) exceeded a critical value, the flow exhibited periodic oscillations in the spanwise direction. These oscillations became significantly stronger with increasing Wi. To evaluate this behavior quantitatively, we utilized micro-PIV to measure the velocity field around micropillars. The resulting velocity fluctuations were then analyzed to determine the dominant frequency of the periodical oscillatory motion. Additionally, flow visualization revealed the formation of dead zones upstream of the first-row pillars, suggesting that their dynamics induce the change in flow direction, thereby enhancing the observed significant oscillations.