Aggregation Scale Eddy Generation During Collective Active Particle Migration: Spectral Energy Flux, Mechanisms, and Impact on Mixing Efficiency

The ocean plays a vital role in regulating Earth’s temperature and weather systems by transporting heat and nutrients throughout its depths. While winds and waves are known to stir the ocean, new research suggests that tiny sea creatures may also play a significant role, collectively generating enough energy to drive substantial mixing. When swimming together in large groups, they can create swirls that are much larger than their individual sizes, potentially strong enough to influence the movement of nutrients up and down in the ocean. This project investigates how swarms of tiny marine animals generate significant water movement, contributing to ocean mixing. By uncovering the mechanisms behind their collective motion, the study aims to improve predictions of ocean behavior and enhance our understanding of marine dynamics. The outcome of the proposed research could potentially benefit engineering applications such as optimizing airflow around drone swarms and improving bubble-induced air-water mixing in wastewater treatment. The project offers training for students and engages the public through accessible educational videos and hands-on workshops. This award will investigate how the collective active migration of small marine organisms can generate large-scale flow structures, referred to as aggregation-scale flows. These flows may contribute meaningfully to vertical mixing in the ocean. The objective of the proposed research is to employ well-controlled laboratory experiments to gain a deeper understanding of aggregation scale flow generation during collective active migrations of particles, an inherently many-body and multi-scale fluid-structure interaction problem. The research is focused on three aims: (1) Identifying the limiting individual and group properties required for generating aggregation scale flows; (2) Understanding the physical mechanisms behind these aggregation scale flows using spatially resolved spectral energy flux analysis; and (3) Directly measuring mixing efficiency using a specialized vertical migration tank designed to mimic relevant ocean stratification scales. This research will test theoretical predictions of mixing efficiency and advance our understanding of collective biological-fluid interactions and their broader effects on ocean mixing and coastal dynamics. Ultimately, the findings will inform the development of improved long-term ocean forecasting models and have broader applications in natural and engineering systems with many-body, fluid-structure interactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.