Computational study of the emergent behavior of micro-swimmer suspensions

Résumé

Recently, we have shown that micro-swimmers in 3D can generate coordinate behaviours like swimming in the same direction or create giant density fluctuations induced by the emergency of a dynamic cluster that percolates in the suspension. We found that the key factor to produce these collective motions (CM) is the hydrodynamic signature of the micro-swimmers. Since the set-up of many experiments is a suspension where particles can move in a quasi-2D geometry, we developed a systematic numerical study such that experimental parameters are simulated. We present here some results of numerical simulations of interacting micro-swimmers constrained to move in a slab. The results prove that our simulations can reproduce perfectly the living clusters obtained by experimentalists for either active colloids or bacteria. We also show some results of spherical swimmers trapped in a plane but embedded in an unconstrained fluid, swimmers can move along the interface and rotate freely in all directions, we found that interactions with the solvent become even more relevant than the 3D or the slab case since more interesting and striking collective motions emerge. To demonstrate that such coordinate behaviours are intrinsic to the hydrodynamic signature of the particles, we developed several systematic studies in terms of the system size. To do such studies it is important to have high performance computing, in our case we had access to the MareNostrum Supercomputer.