UC San Diego

Microswimmers are objects that are able to propel themselves actively in fluid environments. The typical motion of bacteria such as E. coli can be described by the run-and-tumble model, which consists of successive relatively straight runs in conjunction with erratic changes of the swimming direction known as tumbles. The process of diffusion of microswimmers in porous media is crucial in many biological and environmental systems, and their motility is critical for processes such as bioinfection, bioremediation and biodegradation. In this thesis, the diffusion of microswimmers in porous media is studied numerically based on the run-and-tumble model. The results show that an increase in volume fraction of the obstacles comprising the porous medium leads to a decrease in effective long-time diffusivity. In cases where obstables are allowed to overlap, the diffusivity drops even more dramatically with volume fraction than in the case of no overlap. The effect of varying the range of pillar dimensions is also studied. In the case of overlapping pillars, it is found that the diffusivity increases slightly when the domain is filled with