Recirculating flow-induced anomalous transport in meandering open-channel flows

Jun Song Kim, Il Won Seo, Donghae Baek, Peter K. Kang

Research output: Contribution to journalArticlepeer-review

Abstract

Channel meanders in rivers induce complex three-dimensional (3D) flow characteristics such as secondary flows and flow recirculation. Helical secondary flows promote transverse dispersion, and flow recirculation zones trap tracers. As a result, these meander-driven flows may cause anomalous transport manifested by unusually elevated levels of tracer concentration at early and late times of breakthrough curves (BTCs). In this study, we perform 3D numerical simulations in meandering channels across a wide range of channel sinuosity to investigate the impact of meander geometry on flow and transport. We solve 3D Reynolds-averaged Navier-Stoke equations blended with a SST k − ω turbulence model to obtain velocity and turbulence fields. We then incorporate the obtained flow fields into a Lagrangian particle tracking model to simulate solute transport. Sinuosity higher than 1.5 leads to the onset of horizontal recirculating flows along the apex outer banks, and these recirculation zones expand as sinuosity increases. The analysis of the transport simulations elucidates that the interplay between the secondary flows and recirculation zones induces anomalous transport. The helical secondary flows bring particles into the recirculation zones by promoting transverse dispersion, and the recirculating flows delay particle transport by the trapping effect. We show that the tail power-law slope and truncated time of BTCs as well as Lagrangian tortuosity distributions change dramatically with the emergence of recirculation zones. These analyses demonstrate that the recirculation zones are acting as the primary driver of anomalous transport. Finally, we successfully predict the observed anomalous transport with a Spatial Markov Model (SMM), which is an upscaled transport model that incorporates Lagrangian velocity distribution and spatial velocity correlation. The successful predictions show that the Lagrangian velocity statistics effectively capture the underlying mechanisms of anomalous transport in meandering open-channel flows.

Original languageEnglish (US)
Article number103603
JournalAdvances in Water Resources
Volume141
DOIs
StatePublished - Jul 2020

Bibliographical note

Funding Information:
JSK and PKK acknowledge the College of Science & Engineering at the University of Minnesota and the George and Orpha Gibson Endowment, and a grant from Korea Environment Industry and Technology Institute (KEITI) through Subsurface Environmental Management (SEM) Project, funded by the Korea Ministry of Environment(MOE) (2018002440003). IWS and DB also acknowledge support from the Institute of Engineering Research and Institute of Construction and Environmental Engineering in Seoul National University, Seoul, South Korea. We thank the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for computational resources and support.

Funding Information:
JSK and PKK acknowledge the College of Science & Engineering at the University of Minnesota and the George and Orpha Gibson Endowment, and a grant from Korea Environment Industry and Technology Institute ( KEITI ) through Subsurface Environmental Management (SEM) Project, funded by the Korea Ministry of Environment (MOE) ( 2018002440003 ). IWS and DB also acknowledge support from the Institute of Engineering Research and Institute of Construction and Environmental Engineering in Seoul National University, Seoul, South Korea. We thank the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for computational resources and support.

Publisher Copyright:
© 2020 Elsevier Ltd

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

  • Anomalous transport
  • Channel meander
  • Open channel flow
  • Recirculation zone
  • Secondary flow
  • Spatial Markov Model

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