On the Role of Sidewalls in the Transition From Straight to Sinuous Bedforms

Abstract

We present results from direct numerical simulation on the transition from straight‐crested to sinuous‐crested bedforms. The numerical setup is representative of turbulent open channel flow over an erodible sediment bed at a shear Reynolds number of Reτ = 180. The immersed boundary method accounts for the presence of the bed. The simulations are two‐way coupled such that the turbulent flow can erode and modify the bed, and in turn, the bed modifies the overlying flow. Coupling from the flow to the bed occurs through the Exner equation, while back coupling from the bed to the flow is achieved by imposing the no‐slip and no‐penetration condition at the immersed boundary. The simulation setup is similar to that by Zgheib et al. (2018a, https://doi.org/10.1002/2017JF004398) except for the presence of sidewalls to better mimic laboratory flume conditions. Sidewalls are observed to significantly increase bedform sinuosity.

The role of bed-penetrating Kelvin–Helmholtz vortices on local and instantaneous bedload sediment transport

“…2012; Broecker et al. 2018; Zgheib & Balachandar 2019). We should note here that some EE simulations (Cheng, Hsu & Chauchat 2018) consider the sediment–fluid interface to be the location where the sediment bed attains its maximum packing fraction.…”

“…A non-zero fluid velocity at the bed surface has important implications on EE simulations, since most EE simulations use no-slip and no-penetration conditions (Janssen et al 2012;Broecker et al 2018;Zgheib & Balachandar 2019). We should note here that some EE simulations (Cheng, Hsu & Chauchat 2018) consider the sediment-fluid interface to be the location where the sediment bed attains its maximum packing fraction.…”

Influence of Dunes on Channel‐Scale Flow and Sediment Transport in a Sand Bed Braided River

“…Over the past three decades, significant advances have been made in numerical modeling of river processes and evolution using both two‐dimensional “2‐D” depth‐averaged (Baar et al, 2019; Bridge, 1993; Chavarrías et al, 2019; Iwasaki et al, 2016; Lane & Richards, 1998; Langendoen et al, 2016; Nelson, 1990; Nicholas et al, 2013; Osada et al, 2020; Schuurman et al, 2013; Sloff & Mosselman, 2012) and three‐dimensional “3‐D” vertically resolved approaches (Bradbrook et al, 2000; Doré et al, 2016; Giri & Shimizu, 2006; Lane et al, 1999; Nabi et al, 2013; Wu et al, 2000; Yamaguchi et al, 2019; Zgheib & Balachandar, 2019). This body of work has shown that such models are capable of simulating the morphodynamics of a wide range of channel types, including meandering, braided, and anabranching rivers (Baar et al, 2019; Nicholas, 2013; Schuurman et al, 2013, 2016; Schuurman & Kleinhans, 2015; Sun et al, 2015).…”