Lagrangian particle tracking

Lagrangian particle tracking follows individual particles through a flow to calculate or measure their trajectories and transport. It describes motion from each particle’s changing position rather than from values fixed at locations in space.

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Lagrangian reference frame: A description of motion that follows an individual object or fluid parcel through space and time. Particle tracking adopts this moving viewpoint, recording each particle’s changing position.
Lagrangian mechanics: A formulation of classical mechanics based on kinetic and potential energy and the principle of stationary action. Its use of particle paths shares the Lagrangian viewpoint, though tracking is not itself a mechanics formulation.
Lagrangian coherent structure: A material structure in an unsteady flow that organizes transport and separates moving fluid regions. Computed trajectories can expose boundaries that govern transport in complex flows.
Eulerian method: A computational approach that solves flow quantities on fixed spatial locations or grid cells. It computes flow evolution without explicitly following every particle.
Particle advection: The transport of particles by a flow’s velocity field. Advection is the basic motion integrated to produce trajectories in a flow.
Eulerian description: A description of a flow that measures properties at fixed positions in space over time. It provides the fixed-location alternative to following particles through the flow.
Mixing: The redistribution of substances through a medium by fluid motion and molecular diffusion. Particle dispersion quantifies how effectively a flow mixes material.
Computational fluid dynamics: The numerical solution of equations governing fluid motion and related physical processes. Particle tracking can be coupled to a broader fluid simulation as a transport calculation.
Numerical integration: Algorithms that approximate solutions to equations by advancing them through discrete steps. Trajectory calculations advance particle positions through time using numerical integration.
Tracer particle: A particle introduced or identified to reveal the motion of a surrounding fluid. Tracking often uses tracers whose motion approximates that of the fluid.