Capture and interception characteristics of squirmers in a channel flow inserted cylinder

The lattice Boltzmann method (LBM) is used to study the effects of swimming Reynolds number (Re_s), self-propulsion strength (<i>β</i>), squirmer-to-cylinder diameter ratio (<i>δ</i>), and initial position (<i>h</i>) on the capture and interception characteristics of squirmers in a channel flow inserted cylinder. The results show that the squirmer initially located in the cylinder wake will be attracted by the wake, captured by the cylinder, or escape from the wake. For the wake attraction, the pusher (one kind of squirmer) and puller (another kind of squirmer) tend to move farther away from and approach the cylinder, respectively. Cylinder capture occurs only for the puller and depends on <i>β</i> and Re_s. Escape from the wake occurs only for the pusher, and the larger |<i>β</i>|, Re_s and <i>δ</i>, the easier it is to escape. The squirmer initially located upstream of the cylinder exhibits three scenarios, <i>i.e.</i>, intercepted by the cylinder, escape around the cylinder, or wall-hugging escape. The first scenario mainly occurs for the puller, and depends on <i>β</i>, Re_s, <i>δ</i> and <i>h</i>. The second scenario occurs for a puller with low Re_s or <i>β</i>. The third scenario occurs only for the pusher. This study contributes a valuable reference for the control, capture, and classification/sorting of different types of self-propelled particles.