Turbulence Structure In Open-channel Flows Research Articles

Large-eddy simulation of turbulent open-channel flow over three-dimensional dunes

A large-eddy simulation study has been undertaken to investigate the turbulent structure of open-channel flow over three-dimensional (3D) dunes. The governing equations have been discretized using the finite volume method, with the partial cell treatment being implemented in a Cartesian grid form to deal with the 3D dune topography. The simulated free surface elevations, mean flow velocities and Reynolds shear stress distributions have been compared with experimental measurements published in the literature. Relatively close agreement has been obtained between the two sets of results. The predicted mean velocity field and the associated turbulence structure are significantly different from those observed for flows over two-dimensional dunes. The effects of dune three-dimensionality are reflected in spanwise variations of mean flow fields, secondary currents and different distributions of vertical profiles of the double-averaged velocity. Furthermore, large-scale vortical structures, such as spanwise rollers and hairpin-like structures, are predicted in the simulations, with most of them being generated in the concave regions of the 3D dunes.

Large-eddy simulation of the turbulent structure in compound open-channel flows

A large-eddy simulation study has been undertaken to investigate the turbulent structure of open-channel flow in an asymmetric compound channel. The dynamic sub-grid scale model has been employed in the model, with the partial cell treatment being implemented using a Cartesian grid structure to deal with the floodplain. The numerical model was used to predict the: primary velocity and secondary currents, boundary shear stress, turbulence intensities, turbulent kinetic energy, and Reynolds stresses. These parameters were compared with experimental measurements published in the literature, with relatively close agreement being obtained between both sets of results. Furthermore, instantaneous flow fields and large-scale vortical structures were predicted and are presented herein. These vortical structures were found to be responsible for the significant lateral exchange of mass and momentum in compound channels.

A103 植生キャノピー開水路流れの乱流構造の可視化計測

It is important in river environment and hydraulic engineering to reveal the hydrodynamic properties in vegetated open-channel flows, in which velocity profiles are largely changed in the vertical and spanwise directions. In particular, vegetated canopies generate coherent turbulent motions (such as sweeps and ejections) which promote erosions and depositions of sediment on beds.Therefore, it is needed to investigate these turbulence mechanism and coherent vortices in order to maintain the vegetations in actual rivers. In this study, we conducted turbulence measurements by using PIV technique, and revealed the turbulence structure in open-channel flows with vegetated canopies.

Numerical Simulation on Turbulent Structures in Open-Channel Flows over Dunes

The κ-e turbulence model has been developed at present to predict reasonably turbulent structure over dunes in open-channel flows. In closed duct flows and boundary layers, the turbulent structure is reproducted reasonably by relevant models. However, Nezu and Nakagawa (1987) found that the standard κ-e turbulence model can not predict reasonably turbulent structure in open-channel flows, because the turbulence near the surface is more depressed than in the closed duct flows. Therefore, in the present study, the standard κ-e model with generalized coordinate in which the effect of surface is taken into account is used to predict turbulent structure in open-channel flows over dunes. Mean velocity, turbulence characteristics and the effect of surface in open-channel flows over dunes were discussed.

Analysis of Turbulent Structure of Open-Channel Flow with Suspended Sediments

Analysis of Turbulent Structure of Open-Channel Flow with Suspended Sediments