CSDMS 2016 annual meeting poster MahdadTalebpour
Numerical Modelling of Secondary Currents of Second Type Caused by Bed Roughness Variations
Xiaofeng Liu, Pennsylvania State University University Park Pennsylvania, United States.
Abstract:
Secondary current in open channels have been long recognized as an important mechanism to alter the path of sediment particle motion and consequently change the river and land surface evolution. Researchers have identified two different kinds of secondary current: the first kind due to curvature in a river bend and the second kind due to turbulence anisotropy. This study demonstrates numerical investigations of the second kind in straight open channels, induced by bed roughness variations. The study incorporates a non-linear fourth-order k − ω model able to capture anisotropy of turbulence. The k − ω formulation of the model enables implementation of roughness and resolving the near wall flow. This study benefited from an experimental case study to calibrate the roughness parameter implemented in the model. Based on these calibrations, a new range of roughness parameter was introduced enable the model to simulate 3-D flow structure of open channels with rough and smooth strips. For the validation purpose, the model and the new roughness parameter were tested on different case studies. Not only the patterns and mean flow and turbulence statistics were predicted, but also the model was capable of producing almost similar velocity profile for both transverse and vertical directions, along the vertical lines, which have been never shown in previous numerical studies. The results suggest that the arbitrary proposed values in literature are not suitable for simulating open channel flows with different roughness strips on the walls. The calibrated simulation results are further used for more detailed analysis on the momentum and vorticity budget. These analyses would help investigating hypotheses on mechanism of initiation of secondary currents. Furthermore, the data provided by the model will be utilized to model the sediment transport caused by this kind of secondary current in open channels.
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