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Direct Numerical Simulation of Transverse Ripples: 1. Pattern Initiation and Bedform Interactions
Author(s) -
Zgheib N.,
Fedele J. J.,
Hoyal D. C. J. D.,
Perillo M. M.,
Balachandar S.
Publication year - 2018
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1002/2017jf004398
Subject(s) - bedform , turbulence , geology , reynolds number , flow (mathematics) , transverse plane , mechanics , immersed boundary method , open channel flow , geometry , boundary (topology) , physics , sediment transport , geomorphology , sediment , mathematics , engineering , structural engineering , mathematical analysis
We present results of coupled direct numerical simulations between flow and a deformable bed in a horizontally periodic, turbulent open channel at a shear Reynolds number of Re τ = 180 . The feedback between the temporally and spatially evolving bed and the flow is enforced via the immersed boundary method. Using the near‐bed flow field, we provide evidence on the role of locally intense near‐bed vortical structures during the early stages of bed formation, from the emergence of quasi‐streamwise streaks to the formation of incipient bedform crestlines. Additionally, we take a new look at a number of defect‐related bedform interactions, including lateral linking, defect and bedform repulsion, merging, and defect creation, and show that the underlying mechanisms, in these flow‐aligned interactions, are very similar to each other. Consequently, the interactions are labeled differently depending on the geometry of interacting structures and the outcome of the interaction. In the companion paper, we compare our results to published experimental data and provide an extensive quantitative analysis of the bed, where we demonstrate the importance of neighboring structures, especially upstream neighbors, on bedform dynamics (growth/decay and speed) and wave coarsening. Video files of bed evolution are available in the supporting information.