Near-field hydrodynamic interactions play a crucial role in the formation of flagellated microswimmer clusters, yet they are still not clearly understood. In this article, we conduct smoothed dissipative particle dynamics (SDPD) simulations to investigate the clustering/separation process of two identical flagellated microswimmers in non-Newtonian fluid. We also derive autonomous 2-dimensional dynamical systems based on an active sphere-rod model to describe the clustering/separation process. The SDPD simulation results are compared to results of simplified theoretical model to elucidate the influences of flagellum elasticity and fluid viscoelasticity. Our findings show that flagellum elasticity can significantly alter the phase portrait and even trigger a clustering-separation transition. This effect is found to be a result of the the bending of the flagellum's mean centerline under the influence of non-uniform induced flow. While fluid viscoelasticity has a smaller impact on the phase portrait, it notably affects the temporal trajectory of the system. This influence strongly correlates with changes in swimming velocity as fluid viscoelasticity varies. Our results highlight the critical roles that flagellum elasticity may play in the cluster formation of flagellated microswimmers.

Microswimmers,Smoothed Dissipative Particle Dynamics,Fluid-Structure interaction,Non-Newtonian Fluids