Motion characteristics of self-propelled particles in the wake flow past tandem circular cylinders.

The Lattice Boltzmann method (LBM) is used to study the effects of the swimming Reynolds number Res, fluid Reynolds number Re, self-propulsion strength β, and cylinder spacing Δl on the obstacle-bypassing, wall-attached migration, and near-wall equilibrium behaviors of a squirmer in the Poiseuille flow inserted with a fixed tandem dual-cylinder obstacle array. The results show that the squirmer mainly exhibits four motion modes, i.e., downstream bypass, upper wall migration, downward bypass, and lower wall equilibrium. When the Res or |β| is small, the squirmer mainly undergoes downstream bypass, indicating that the background flow field and wake structure play dominant roles. As the self-propulsion is strengthened, the puller changes to downward bypass and further forms a lower wall equilibrium. For the pusher, gap-mediated obstacle escape occurs first, followed by upper wall migration under stronger self-propulsion conditions. Increasing Δl changes the wake structure in the gap region, thereby regulating the local obstacle-bypassing trajectory, wall contact turning point, and equilibrium position of the particle. Re further regulates the characteristic trajectory parameters and can induce transitions between swimming modes. This study provides a useful reference for the trajectory control of self-propelled particles in confined microchannels.