Interface-resolved simulations of particles in active nematics

Abstract

An accurate coarse-grained simulation of an active fluid is invaluable as a tool to understand its hydrodynamic behaviors. The study on the dynamics of particles immersed in an active fluid also requires accurate resolution of the fluid–particle interaction. In this paper, we propose a robust direct forcing fictitious domain method to study the dynamics of suspended particles in an active fluid modeled by “active nematics.” This method serves as both a coarse-grained approach and an accurate model of fluid–particle interaction. We first validate the method by computing the kinetic energy spectrum for the bulk active nematics and find that it accurately reproduces the scaling laws reported theoretically and experimentally. By utilizing these interface-resolved simulations, we illustrate that the model's activity parameter cannot be simply considered as the concentration of bacterial suspensions. Moreover, we find that the diffusion coefficient DT of an individual disk is relevant to the length scale lc of the active nematics, following a power-law scaling DT ∼ lc−1.5. Regarding collective dynamics, we discover a self-organized length scale of approximately 7.5 times the disk's diameter in the active nematics. Additionally, the disks modify the kinetic energy spectrum of the active nematics at both the self-organized length scale and the individual disk's diameter scale, respectively.