Numerical simulation of flow field over trains of bed-load dunes: insights and recommendations

Bed-load dunes significantly impact flow resistance and sediment transport. Computational Fluid Dynamics simulation of the complex turbulent flow over them is a powerful, high-resolution alternative to challenging lab measurements. This study uses a Reynolds-Averaged Navier-Stokes solver with the Volume-of-Fluid method to simulate the flow over triangular dunes. First, preliminary tests were performed simulating gradually-varied-flow profiles in open channels, to establish suitable boundary conditions that could make the Volume-of-Fluid approach return reliable results. Second, the model was validated against literature experiments for both plane and dune-covered beds. For the plane bed, the inlet flow distribution was the most impactful parameter, and the Reynolds-Stress Model outperformed the standard k - ε model. For the dune-bed simulations, that were run with the Reynolds-Stress Model, a mesh sensitivity analysis was carried out; furthermore, the effect of the inlet velocity distribution was also investigated.