Author(s): D. Sofialidis; P. Prinos

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Abstract: The effect of flood plain roughness in compound open channel flow is studied numerically with a low- Reynolds k-ω model, which is non-linear and therefore capable of predicting the turbulence anisotropy and the turbulence-driven secondary currents. The simulation of rough walls is achieved through a simple boundary condition for ω at the top of the roughness. Free surface modelling is also included, based on an empirical approach. For relative roughness greater than unity the lateral shear layer that develops at the main channelflood plain interface is intensified. The velocities follow the logarithmic law in the interaction region for high and low relative depths with smooth and rough flood plains. Secondary currents and turbulent shear stresses are reproduced well by the model when compared with available measurements and are found greater in the interaction region as relative roughness increases. Turbulent intensities are captured sufficiently with a slight underestimation of u' near the channel bed. Turbulence is enhanced at the interface when the flood plain bed is rough and remains unaffected in the rest of the flow. The free surface simulation is proved capable of reproducing the depression of the maximum velocity below the free surface which becomes more pronounced with increasing relative roughness.

DOI: https://doi.org/10.1080/00221689909498520

Year: 1999