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 Re_s, 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 Re_s 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.