Energy-vortex-momentum coupling bridges hydrodynamics and mass transfer of perfluoroalkyl acids

Perfluoroalkyl acids (PFAAs) accumulated in sediments can be remobilized under strong hydrodynamic disturbance, yet the mechanistic pathways linking turbulent flow structures to sediment-water mass transfer remain poorly resolved. Propeller clearance height (h_c) acts as a controlling geometric boundary condition that governs whether energetic vortices can directly interact with the sediment bed and induce PFAA release. Here, controlled flume experiments conducted at varying h_c elucidate how jet energy, mediated by vortex structures, drives PFAA migration. Changes in h_c markedly altered the spatial distribution of energy and the morphology of vortices, thereby controlling multiphase PFAA migration. At low h_c, energy concentrated near the bed, forming clustered large vortices and high shear that promoted intensive PFAA release from sediments and porewater. The released PFAAs accumulated mainly in bottom overlying water and suspended particulate matter, with their behavior affected by carbon-fluorine chain length, functional group type, and water chemical parameters. Increasing h_c weakened direct bed disturbance while enhancing vertical mixing through medium- and small-scale vortices, facilitating dilution and long-range diffusion. Further analysis revealed that energy transport pathways, vortex dynamics, and transient coherent events jointly governed PFAA mass transfer. This study provides the first mechanistic insight into PFAA transport under strong turbulence from an integrated energy-vortex-mass transfer perspective, offering a theoretical basis for managing sediment-derived pollutants in navigable waters.