Detailed simulation of morphodynamics: 3. Ripples and dunes

Abstract

[1] We present a 3-D physics-based high-resolution modeling approach to the dynamics of underwater ripples and dunes. The flow is modeled by large eddy simulation on a Cartesian grid with local refinements. The sediment transport is modeled by computing pickup, transport over the bed, transport in the water column, and deposition of rigid spherical particles in a Lagrangian framework. The morphological development of the bed is modeled by a sediment balance equation in which the pickup and deposition from the sediment motion submodels appear as source and sink terms. The model realistically replicated the formation and migration of dunes. Model results showed a good agreement with data from five flume experiments. We subsequently applied the model to investigate the effect of sediment grain size on ripples. Finer sediments were found to yield more superimposed ripples than coarser sediments. Moreover, under the same hydrodynamic conditions, the finer sediments yielded two-dimensional bed forms, whereas for coarser sediment irregularities increased. We extended the tests to pronounced 3-D morphologies by simulating the development of local scour at a pier. The results agreed well with experimental data. The model contributes to unraveling the complex problem of small-scale morphodynamics and may be used in a wide range of applications, for instance, to develop more reliable parameterizations of small-scale processes for application in large-scale morphodynamic models.

Computational Modeling of Flow and Scour around Two Cylinders in Staggered Array

“…We employed our previously developed LES model, combined with sediment transport and morphodyanmic models [23][24][25][26] to simulate the coupled hydrodynamic and morphodynamic processes around two circular cylinders in a staggered array. The numerical model was composed of three submodels including hydrodynamic, sediment transport, and morphodynamic models.…”

“…In order to overcome the inherent limitations of RANS model, the large eddy simulation (LES) or detached eddy simulation (DES) models coupled with a morphodynamic model have been developed [22][23][24]. Escauriaza and Sotiropoulos [22] who developed the DES model, investigated the initial stage of scour in the vicinity of a circular cylinder.…”

Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics

“…Eddy-resolving simulation techniques such as large-eddy simulation (LES) and detached eddy simulation (DES), or lattice Boltzmann methods, then become necessary. The utility of eddy-resolving methods has been demonstrated by the explosion of the number of studies in the last few years, with applications to flow around channel obstacles and their associated scour holes [Kirkil et al, 2008;Koken and Constantinescu, 2009], flow through vegetation [Kim and Stoesser, 2011], as well as sediment transport [Nabi et al, 2012[Nabi et al, , 2013aSchmeeckle, 2014] and flow over bed forms [Nabi et al, 2013b;Chang and Constantinescu, 2013;Omidyeganeh and Piomelli, 2013], and flow through channel confluences [Constantinescu et al, 2011a]. See Keylock et al [2005] for an early introduction to the use of LES in channel flow hydraulics and Keylock et al…”

Morphodynamics of river dunes : suspended sediment transport along mobile dunes and dune development towards upper stage plane bed

“…Other important direction for future research is linking the results of this study to complex numerical models that describe the turbulent flow and sediment concentration above dunes [e.g., Nabi et al, 2013]. In particular, under same flow and bed conditions, the complex numerical models should be able to reproduce the contribution of the turbulent fluxes to the total fluxes observed in this study.…”

“…By deploying the ACVP in the present study, we are able to measure -for the first timethe contribution of the turbulent sediment flux to the total sediment flux along the dune profile and over the entire water column. Beyond a better understanding of the physical interaction processes between the flow and the transported sediments, these insights can be used for validation of complex numerical models that predict the turbulent flow and sediment concentration above bed forms [e.g., Nabi et al, 2013]. Moreover, such unique high-resolution data are useful for the improvement -via calibration -of engineering codes modeling sediment transport.…”