Wall-modeled Large-Eddy Simulation of the flow over a realistic riverine geometry

This research focuses on sediment transport and the formation of bedforms in turbulent river flows, under flow conditions typical of flooding events.

Through the implementation of an immersed boundary method, a wall model, and a morphological model we were able to simulate complex and mobile geometries under high Reynolds numbers at an affordable computational cost.

After validation against numerical and experimental data, we simulated the evolution of bedforms on a loose sediment bed under turbulent flow conditions, using input parameters obtained from laboratory measurements. Over time, the bedforms become more three-dimensional and irregular in shape, leading to changes in the shear layer, crest angle, and separation patterns. The bedforms continue to evolve until a quasi-steady equilibrium is reached.

The presence of small-scale bedforms significantly affects the flow dynamics: an increase in the total drag is observed, related to the form drag generated by the local recirculation and the increased size of the large-scale separation bubble. Furthermore, a stronger turbulent activity ensues from the shear layers forming on the crests of the small-scale bedforms.

Finally, a wider shedding angle of the shear layer is caused by the irregular crest line.