Computational Dynamics of Interfaces in Multispecies Active Fluids

Capturing the behavior of interactions between the collective motion of mismatched swarms of active agents is critical to the understanding of natural phenomena and several new developments in engineering and medicine. The simple locomotive rules applied to each agent give way to emergent behavior of the whole swarms and the interface between them. Here we define the interface as the curve delimiting the region where one species predominates, and study how its evolution is related to the swimming properties. We focus in particular on the emergence of spontaneous structures, and investigate whether these structures can be compared to traditional crystals. We use a multi-scale mean-field continuum model to simulate the motion of active agents, without tracking agents themselves, and couple their governing equations with that of the surrounding fluid. The resulting continuum system is solved using a level-set based hybrid Finite Difference-Finite Volume solver on a Quadtree grid for high computational efficiency. This work is an advancement on the method presented by us earlier and continues to pave the way for future studies of systems which can be described as the collective motion of active agents, such as bacterial colonies, wound healing, colloidal swimmers, and programmable active matter. In nature, swarming species certainly interact, and we seek to understand the mechanisms which govern the behavior of the collective motion of active agents when encountering another swarm.