Numerical simulation of swash flow using openfoam

Nikolaos Karagiannis, Anastasios Stampoultzoglou, Panayotis Prinos

Monday 29 june 2015

14:35 - 14:50h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 2C. Coastal engineering

The aim of this work is to simulate a swash flow, generated by bore collapse, on rough beaches. It is the instantaneous generation of this kind of flow that creates specific turbulent and unsteadiness conditions in a very short time period and it is very difficult for a numerical model to simulate exactly the physical process. The flow was numerically simulated with the open source software OpenFoam. VOF method was used in order for the free surface to be tracked and two turbulence models (RNG k-_ and k-_ SST models) for incompressible flow (available in OpenFoam libraries), were modified in order for the density to be included in model's equations and the simulation of the free surface to be improved. Furthermore, suitable boundary and initial conditions were chosen with the k, epsilon and omega ones being extremely important for the correct simulation of this kind of flow. So, extended investigation was made for the correct k-_(of the RNG k-_ model) and k-_ (of the k-_ SST model) initial conditions for the initiation and propagation of the turbulent bore at early stages. After defining the most appropriate initial values, the results of the two models are compared with experimental data (Kikkert et al. 2012). Numerical velocities and turbulent kinetic energy profiles at specific times, depth average velocities, surface elevation and bed shear stress are presented for the two turbulence models with different k-_ and k-_ initial values and are compared satisfactorily with available experimental measurements (Kikkert et al. 2012). In conclusion, k-_ or k-_ initial conditions are very crucial for the successful numerical simulation of the aforementioned swash flow. It is found that the RNG k-_ model with the following initial conditions: k=_= 0.2 yields better results than the k-_ SST in comparison with the experimental measurements. References : 1.Kikkert G.A., O’Donoghue T., Pokrajac D., Dodd N. (2012), “Experimental study of bore-driven swash hydrodynamics on impermeable rough slopes”, Coastal Engineering, 60, 149-166.