183Effect of Peclet number on MIPS in a four-roll-mill flow

We numerically investigate a system of active Brownian particles (ABPs) in a periodic four-roll-mill flow. In the absence of flow, the system undergoes motility-induced phase separation (MIPS). When a four-roll-mill flow is introduced, flow-induced phase separation (FIPS) occurs, with particles clustering in strain-dominated regions. Our study focuses on the influence of the Peclet number (Pe), a dimensionless ratio of rotational diffusion to self-propulsion time-scale, on both MIPS and FIPS. We examine the impact of Pe on the cluster size distribution and giant number fluctuations. We find that increasing Pe leads to larger clusters in both systems. However, the presence of background flow results in relatively smaller clusters. The cluster size distribution exhibits a power-law decay, with the exponent initially decreasing and then plateauing as Pe increases. Notably, the decay is steeper in the absence of flow. Additionally, we observe that number fluctuations scale with the mean particle number as a power law. The background flow reduces the exponent of this power-law scaling.