Three dimensional simulation of flow field around series of spur dikes

Erosion of the banks and bed of natural and manmade channels is a common problem in water resources management. Spur dikes in rivers and streams such as the Mississippi River are used to prevent bank erosion and to keep the main channel navigable. Scour around these dikes can be a serious problem, weakening structural stability. Three-dimensional models are often used in engineering design to determine mean and turbulence flow field around these dikes. However, a universal turbulent model that is valid for all cases of turbulent flow in open channels currently does not exist. Some turbulent closures offer advantages over others in specific turbulent flow fields depending on the nature of turbulence. Therefore, a three-dimensional numerical model, FLOW-3D, is used to simulate the turbulent flow field around a series of three spur dikes in flat and scoured bed. This study examined one equation mixing length model, standard two-equation k - ε model, Renormalization Group (RNG) k - ε model and Large Eddy Simulation (LES) model. Experimental data from a laboratory study of flow in a flat bed and scoured bed around a series of three dikes were used to verify the results from the numerical model. Although the simulated mean flow field is close to the experimental data, the simulated turbulence properties from different turbulent model deviate considerably. Modeling results using the standard k - ε model showed over 50 discrepancy from the measured turbulent kinetic energy. The RNG k - ε model yielded better results of both mean flow field and turbulence kinetic energy for the flat bed surface and scoured bed surface. Based on these results, this study recommends the use of RNG k - ε model for simulating mean flow field around dikes. Further improvements of FLOW-3D model is needed for predicting turbulence properties (e.g. TKE) near this series of spur dikes under various flow conditions.