Compound Open-Channel Flow Modeling with Nonlinear Low-Reynolds k -ε Models

Turbulent flow in compound open channels is studied numerically with nonlinear k-ε turbulence models of low-Reynolds type. Emphasis is given to the flow characteristics and the performance of the models for conditions of low relative depths (up to 0.2547) for which the interaction between main channel and flood plain flow is significant. Experiments and computations indicate that the velocities follow the law of the wall in the interaction region even for such low relative depths. Secondary currents are predicted by a modified version of a previous model; however, the predicted currents are not as strong as the experimental ones. Turbulent shear stresses and especially -uw¯, which is significant for low relative depths, are predicted reasonably by the model, except in the interaction region in the main channel. The turbulent intensities v′ and w′ are captured by the model while u′ is underestimated. A depth-averaged analysis identifies two basic mechanisms that influence the variation of the bed shear stress and suggests a means of assessing the contribution of each mechanism to the deviation of the bed shear stress from its respective two-dimensional value.