Taylor dispersion of particles under surface waves

The transport of buoyant particles in the ocean, such as microplastics, oil droplets, and bubbles, is largely influenced by the free surface boundary layer, including surface waves and turbulence. These particles accumulate at the free surface, but turbulence can mix them downward, distributing them throughout the vertically sheared flow. This causes particles to move at different relative speeds, enhancing their streamwise spreading, commonly known as Taylor dispersion. The rate and magnitude of this dispersion is primarily controlled by the wave parameters, particle rise velocity, and turbulent diffusivity profile. In this talk, we investigate the Taylor dispersion of particles suspended under waves, separating the effects of the unsteady, fast orbital motion from the slow Stokes drift. We derive an analytical model to estimate the influence of wave steepness, relative wave depth, and Peclet number characterized by the rise velocity and wave amplitude. Lastly, we contrast our results with a numerical simulation, which shows similar trends to the analytical model.