Flow and bathymetry in sharp open‐channel bends: Experiments and predictions

Abstract

[1] This paper focuses on experiments and simulations conducted in very sharp open-channel bends with flat and equilibrium bathymetry, corresponding to the initial and final phases of the erosion and deposition processes, respectively. The study of flow in curved open bends is relevant for flow in natural river configurations, as most river reaches are not straight. The configuration considered in the present work was designed as a test case in which the role of the cross-sectional flow is more severe than in meandering natural river reaches (radius of curvature of the channel is close to the channel width) and, thus, can serve for validation of numerical models used to predict flow and sediment transport in river engineering applications. This paper presents detailed new experimental data on the equilibrium bathymetry as well as depth-averaged distributions, vertical profiles, and cross-sectional patterns of the streamwise velocity, the cross-stream circulation, streamwise vorticity, and the turbulent kinetic energy at the initial and final stages of the erosion and deposition processes. The numerical simulations are performed using a three-dimensional nonhydrostatic RANS model for flow, sediment transport, and bathymetry, which employs fine meshes, accounts for the effect of small bed forms, and avoids the use of the law of the wall. The model predicts, rather accurately, the distribution of the streamwise velocity, the cross-stream circulation, and the turbulent kinetic energy in the simulations conducted with a fixed (flat and deformed bed corresponding to equilibrium conditions) prescribed bathymetry. In the case of a simulation conducted with loose bed, the model predicts satisfactorily the main features of the bathymetry at equilibrium conditions, despite the fact that including the interaction between the flow and the bathymetry increases the overall uncertainty in the model predictions. Results indicate that both improvements in the level of turbulence modeling and in the modeling of the sediment transport would allow further improvement in the predictive capabilities of morphodynamic models.

Large-eddy simulation of a curved open-channel flow over topography

“…The dynamic ripples moving along the bed are parametrized with an equivalent roughness height of k s = 0.037 m. This value consists of a contribution from the roughness of the sand particles themselves and a contribution from the unresolved bed forms and is equal to the k s value taken by Zeng et al 14 However, considering the speculative nature of this choice, the sensitivity of changes in this value is investigated by means of two additional simulations: one with k s = 0.006 m and one with a k s value varying from 0.006 m at the most shallow point of the bed to 0.037 m at the deepest point of the bed.…”

“…The aim of the present paper is to contribute to the existing body of literature on curved open-channel flows in general and the papers by Blanckaert 13 and Zeng et al 14 These four research questions are subsumed in separate sections in the paper. After a description of the experimental setup and the large-eddy simulation model in Sec.…”

“…7, the profiles of the velocities in streamwise and transverse direction are shown as these follow from the experiment and the LES computation. In addition, the results from the RANS computation are taken from the paper by Zeng et al 14 and shown in Fig. 7 as well.…”

Wall-Roughness Effects on Flow and Scouring in Curved Channels with Gravel Beds

“…The flow structure and related scouring effects in bends have been studied empirically (i.e., Blanckaert and De Vriend 2004;Blanckaert and Graf 2004;Abad and Garcia 2009;Sukhodolov 2012), numerically (i.e., van Balen et al 2009;Zeng et al 2008), and theoretically (i.e., Odgaard and Bergs 1988;Johannesson and Parker 1989;Blanckaert et al 2013). Fargue (1868) was probably the first to publish a formula for scour in river bends, based on field observation.…”

Simulation of open channel bend characteristics using computational fluid dynamics and artificial neural networks

“…Email: bonakdari@yahoo.com Graf (2001) conducted experimental studies on turbulent flow in a movable bed with a 120°sharp bend. Zeng, Constantinescu, Blanckaert, and Weber (2008) experimentally examined the velocity patterns, vorticity, turbulent kinetic energy, and bathymetry of a 193°sharp bend. Ramamurthy, Han, and Biron (2013) conducted vast experimental and numerical research studies on the velocity profiles of sharp bends.…”