DEVELOPMENT AND VALIDATION OF A 3D NUMERICAL MODEL TO SIMULATE FLOODS IN NATURAL STREAMS

The paper discusses the development and validation of a 3D RANS model using the commercial code STAR-CCM+ to simulate flooding in natural streams. The Volume of Fluid (VOF) method is used to calculate the deformations of the free surface. The k-omega turbulence model is used to account for turbulence effects. Simulations conducted for this type of applications conducted on meshes containing 1-10 million grid cells show that the code scales well. Validation results are presented for a standard test case corresponding to steady flow in an S-shaped open channel of trapezoidal cross section. The predictions of the free surface deformations and streamwise velocity profiles in selected cross sections are found to agree well with experimental data. Then, the model is applied to predict flow and free surface elevations in a 1-km long reach of the Iowa River near Iowa City. The simulation successfully captures the centerline variation of the free surface elevation, while mass conservation errors are small across the domain. Ongoing applications of the present model include performing unsteady flow simulations corresponding to the propagation of a flood wave in a natural channel and assessing the performance and limitations of popular 2D models used to predict flood propagation in natural environments.