Lagrangian flow networks for passive dispersal: tracers versus finite size particles

TL;DR

This study evaluates the accuracy of using tracer particles to model the transport of inertial particles in oceanic and industrial flows, highlighting significant differences based on particle properties and flow conditions.

Contribution

It introduces a Lagrangian flow network model incorporating inertial particle dynamics and flow geometry, revealing limitations of the tracer approximation for certain particle types.

Findings

Transport probabilities depend on particle properties, flow, and geometry.

Strong segregation observed between aerosols and bubbles.

Tracer approximation may mispredict particle transport in some cases.

Abstract

The transport and distribution of organisms like larvae, seeds or litter in the ocean as well as particles in industrial flows is often approximated by a transport of tracer particles. We present a theoretical investigation to check the accuracy of this approximation by studying the transport of inertial particles between different islands embedded in an open hydrodynamic flow aiming at the construction of a Lagrangian flow network reflecting the connectivity between the islands. To this end we formulate a two-dimensional kinematic flow field which allows the placement of an arbitrary number of islands at arbitrary locations in a flow of prescribed direction. To account for the mixing in the flow we include a von K\'arm\'an vortex street in the wake of each island. We demonstrate that the transport probabilities of inertial particles making up the links of the Lagrangian flow network depend essentially on the properties of the particles, i.e. their Stokes number, the properties of the flow and the geometry of the setup of the islands. We find a strong segregation between aerosols and bubbles. Upon comparing the mobility of inertial particles to that of tracers or neutrally buoyant particles, it becomes apparent that the tracer approximation may not always accurately predict the probability of movement. This can lead to inconsistent forecasts regarding the fate of marine organisms, seeds, litter or particles in industrial flows.