Experimental study of particle trajectories below deep-water surface gravity wave groups

T. S. Van Den Bremer, C. Whittaker, R. Calvert, A. Raby, P. H. Taylor

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


Owing to the interplay between the forward Stokes drift and the backward wave-induced Eulerian return flow, Lagrangian particles underneath surface gravity wave groups can follow different trajectories depending on their initial depth below the surface. The motion of particles near the free surface is dominated by the waves and their Stokes drift, whereas particles at large depths follow horseshoe-shaped trajectories dominated by the Eulerian return flow. For unidirectional wave groups, a small net displacement in the direction of travel of the group results near the surface, and is accompanied by a net particle displacement in the opposite direction at depth. For deep-water waves, we study these trajectories experimentally by means of particle tracking velocimetry in a two-dimensional flume. In doing so, we provide visual illustration of Lagrangian trajectories under groups, including the contributions of both the Stokes drift and the Eulerian return flow to both the horizontal and the vertical Lagrangian displacements. We compare our experimental results to leading-order solutions of the irrotational water wave equations, finding good agreement.

Original languageEnglish
Pages (from-to)168-186
Number of pages19
JournalJournal of Fluid Mechanics
Publication statusPublished - 25 Nov 2019


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