Visualization of three-dimensional velocity field around a micropillar in dilute polymer-solution flow by astigmatism PTV

In this study, we aimed to visualize the three-dimensional flow field in the low-speed region formed upstream of a circular micropillar in a microchannel using astigmatism PTV (APTV) technique, when a dilute solution of hydrolyzed polyacrylamide, which is a typical non-Newtonian fluid, was infused into the channel. From the sequentially distorted particle images, the presence of rotational flow in the low-speed region was identified. The three-dimensional velocity field revealed by APTV showed complex flow behavior, and alternating upward and downward structures in the w component of the velocity, corresponding to the heightwise direction in the channel, appeared upstream of the micropillar. Additionally, the value of the normalized w component in the low-speed region decreased as the shear rate increased around the micropillar.